text: // Copyright 2011 the V8 project authors. All rights reserved.
  // Redistribution and use in source and binary forms, with or without
  // modification, are permitted provided that the following conditions are
  // met:
  //
  //     * Redistributions of source code must retain the above copyright
  //       notice, this list of conditions and the following disclaimer.
  //     * Redistributions in binary form must reproduce the above
  //       copyright notice, this list of conditions and the following
  //       disclaimer in the documentation and/or other materials provided
  //       with the distribution.
  //     * Neither the name of Google Inc. nor the names of its
  //       contributors may be used to endorse or promote products derived
  //       from this software without specific prior written permission.
  //
  // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  
  #include "v8.h"
  
  #include "ast.h"
  #include "compiler.h"
  #include "execution.h"
  #include "factory.h"
  #include "jsregexp.h"
  #include "platform.h"
  #include "string-search.h"
  #include "runtime.h"
  #include "compilation-cache.h"
  #include "string-stream.h"
  #include "parser.h"
  #include "regexp-macro-assembler.h"
  #include "regexp-macro-assembler-tracer.h"
  #include "regexp-macro-assembler-irregexp.h"
  #include "regexp-stack.h"
  
  #ifndef V8_INTERPRETED_REGEXP
  #if V8_TARGET_ARCH_IA32
  #include "ia32/regexp-macro-assembler-ia32.h"
  #elif V8_TARGET_ARCH_X64
  #include "x64/regexp-macro-assembler-x64.h"
  #elif V8_TARGET_ARCH_ARM
  #include "arm/regexp-macro-assembler-arm.h"
  #elif V8_TARGET_ARCH_MIPS
  #include "mips/regexp-macro-assembler-mips.h"
  #else
  #error Unsupported target architecture.
  #endif
  #endif
  
  #include "interpreter-irregexp.h"
  
  
  namespace v8 {
  namespace internal {
  
  Handle<Object> RegExpImpl::CreateRegExpLiteral(Handle<JSFunction> constructor,
                                                 Handle<String> pattern,
                                                 Handle<String> flags,
                                                 bool* has_pending_exception) {
    // Call the construct code with 2 arguments.
    Handle<Object> argv[] = { pattern, flags };
    return Execution::New(constructor, ARRAY_SIZE(argv), argv,
                          has_pending_exception);
  }
  
  
  static JSRegExp::Flags RegExpFlagsFromString(Handle<String> str) {
    int flags = JSRegExp::NONE;
    for (int i = 0; i < str->length(); i++) {
      switch (str->Get(i)) {
        case 'i':
          flags |= JSRegExp::IGNORE_CASE;
          break;
        case 'g':
          flags |= JSRegExp::GLOBAL;
          break;
        case 'm':
          flags |= JSRegExp::MULTILINE;
          break;
      }
    }
    return JSRegExp::Flags(flags);
  }
  
  
  static inline void ThrowRegExpException(Handle<JSRegExp> re,
                                          Handle<String> pattern,
                                          Handle<String> error_text,
                                          const char* message) {
    Isolate* isolate = re->GetIsolate();
    Factory* factory = isolate->factory();
    Handle<FixedArray> elements = factory->NewFixedArray(2);
    elements->set(0, *pattern);
    elements->set(1, *error_text);
    Handle<JSArray> array = factory->NewJSArrayWithElements(elements);
    Handle<Object> regexp_err = factory->NewSyntaxError(message, array);
    isolate->Throw(*regexp_err);
  }
  
  
  // Generic RegExp methods. Dispatches to implementation specific methods.
  
  
  Handle<Object> RegExpImpl::Compile(Handle<JSRegExp> re,
                                     Handle<String> pattern,
                                     Handle<String> flag_str) {
    Isolate* isolate = re->GetIsolate();
    JSRegExp::Flags flags = RegExpFlagsFromString(flag_str);
    CompilationCache* compilation_cache = isolate->compilation_cache();
    Handle<FixedArray> cached = compilation_cache->LookupRegExp(pattern, flags);
    bool in_cache = !cached.is_null();
    LOG(isolate, RegExpCompileEvent(re, in_cache));
  
    Handle<Object> result;
    if (in_cache) {
      re->set_data(*cached);
      return re;
    }
    pattern = FlattenGetString(pattern);
    ZoneScope zone_scope(isolate, DELETE_ON_EXIT);
    PostponeInterruptsScope postpone(isolate);
    RegExpCompileData parse_result;
    FlatStringReader reader(isolate, pattern);
    if (!RegExpParser::ParseRegExp(&reader, flags.is_multiline(),
                                   &parse_result)) {
      // Throw an exception if we fail to parse the pattern.
      ThrowRegExpException(re,
                           pattern,
                           parse_result.error,
                           "malformed_regexp");
      return Handle<Object>::null();
    }
  
    if (parse_result.simple && !flags.is_ignore_case()) {
      // Parse-tree is a single atom that is equal to the pattern.
      AtomCompile(re, pattern, flags, pattern);
    } else if (parse_result.tree->IsAtom() &&
        !flags.is_ignore_case() &&
        parse_result.capture_count == 0) {
      RegExpAtom* atom = parse_result.tree->AsAtom();
      Vector<const uc16> atom_pattern = atom->data();
      Handle<String> atom_string =
          isolate->factory()->NewStringFromTwoByte(atom_pattern);
      AtomCompile(re, pattern, flags, atom_string);
    } else {
      IrregexpInitialize(re, pattern, flags, parse_result.capture_count);
    }
    ASSERT(re->data()->IsFixedArray());
    // Compilation succeeded so the data is set on the regexp
    // and we can store it in the cache.
    Handle<FixedArray> data(FixedArray::cast(re->data()));
    compilation_cache->PutRegExp(pattern, flags, data);
  
    return re;
  }
  
  
  Handle<Object> RegExpImpl::Exec(Handle<JSRegExp> regexp,
                                  Handle<String> subject,
                                  int index,
                                  Handle<JSArray> last_match_info) {
    switch (regexp->TypeTag()) {
      case JSRegExp::ATOM:
        return AtomExec(regexp, subject, index, last_match_info);
      case JSRegExp::IRREGEXP: {
        Handle<Object> result =
            IrregexpExec(regexp, subject, index, last_match_info);
        ASSERT(!result.is_null() || Isolate::Current()->has_pending_exception());
        return result;
      }
      default:
        UNREACHABLE();
        return Handle<Object>::null();
    }
  }
  
  
  // RegExp Atom implementation: Simple string search using indexOf.
  
  
  void RegExpImpl::AtomCompile(Handle<JSRegExp> re,
                               Handle<String> pattern,
                               JSRegExp::Flags flags,
                               Handle<String> match_pattern) {
    re->GetIsolate()->factory()->SetRegExpAtomData(re,
                                                   JSRegExp::ATOM,
                                                   pattern,
                                                   flags,
                                                   match_pattern);
  }
  
  
  static void SetAtomLastCapture(FixedArray* array,
                                 String* subject,
                                 int from,
                                 int to) {
    NoHandleAllocation no_handles;
    RegExpImpl::SetLastCaptureCount(array, 2);
    RegExpImpl::SetLastSubject(array, subject);
    RegExpImpl::SetLastInput(array, subject);
    RegExpImpl::SetCapture(array, 0, from);
    RegExpImpl::SetCapture(array, 1, to);
  }
  
  
  Handle<Object> RegExpImpl::AtomExec(Handle<JSRegExp> re,
                                      Handle<String> subject,
                                      int index,
                                      Handle<JSArray> last_match_info) {
    Isolate* isolate = re->GetIsolate();
  
    ASSERT(0 <= index);
    ASSERT(index <= subject->length());
  
    if (!subject->IsFlat()) FlattenString(subject);
    AssertNoAllocation no_heap_allocation;  // ensure vectors stay valid
  
    String* needle = String::cast(re->DataAt(JSRegExp::kAtomPatternIndex));
    int needle_len = needle->length();
    ASSERT(needle->IsFlat());
  
    if (needle_len != 0) {
      if (index + needle_len > subject->length()) {
        return isolate->factory()->null_value();
      }
  
      String::FlatContent needle_content = needle->GetFlatContent();
      String::FlatContent subject_content = subject->GetFlatContent();
      ASSERT(needle_content.IsFlat());
      ASSERT(subject_content.IsFlat());
      // dispatch on type of strings
      index = (needle_content.IsAscii()
               ? (subject_content.IsAscii()
                  ? SearchString(isolate,
                                 subject_content.ToAsciiVector(),
                                 needle_content.ToAsciiVector(),
                                 index)
                  : SearchString(isolate,
                                 subject_content.ToUC16Vector(),
                                 needle_content.ToAsciiVector(),
                                 index))
               : (subject_content.IsAscii()
                  ? SearchString(isolate,
                                 subject_content.ToAsciiVector(),
                                 needle_content.ToUC16Vector(),
                                 index)
                  : SearchString(isolate,
                                 subject_content.ToUC16Vector(),
                                 needle_content.ToUC16Vector(),
                                 index)));
      if (index == -1) return isolate->factory()->null_value();
    }
    ASSERT(last_match_info->HasFastElements());
  
    {
      NoHandleAllocation no_handles;
      FixedArray* array = FixedArray::cast(last_match_info->elements());
      SetAtomLastCapture(array, *subject, index, index + needle_len);
    }
    return last_match_info;
  }
  
  
  // Irregexp implementation.
  
  // Ensures that the regexp object contains a compiled version of the
  // source for either ASCII or non-ASCII strings.
  // If the compiled version doesn't already exist, it is compiled
  // from the source pattern.
  // If compilation fails, an exception is thrown and this function
  // returns false.
  bool RegExpImpl::EnsureCompiledIrregexp(Handle<JSRegExp> re, bool is_ascii) {
    Object* compiled_code = re->DataAt(JSRegExp::code_index(is_ascii));
  #ifdef V8_INTERPRETED_REGEXP
    if (compiled_code->IsByteArray()) return true;
  #else  // V8_INTERPRETED_REGEXP (RegExp native code)
    if (compiled_code->IsCode()) return true;
  #endif
    // We could potentially have marked this as flushable, but have kept
    // a saved version if we did not flush it yet.
    Object* saved_code = re->DataAt(JSRegExp::saved_code_index(is_ascii));
    if (saved_code->IsCode()) {
      // Reinstate the code in the original place.
      re->SetDataAt(JSRegExp::code_index(is_ascii), saved_code);
      ASSERT(compiled_code->IsSmi());
      return true;
    }
    return CompileIrregexp(re, is_ascii);
  }
  
  
  static bool CreateRegExpErrorObjectAndThrow(Handle<JSRegExp> re,
                                              bool is_ascii,
                                              Handle<String> error_message,
                                              Isolate* isolate) {
    Factory* factory = isolate->factory();
    Handle<FixedArray> elements = factory->NewFixedArray(2);
    elements->set(0, re->Pattern());
    elements->set(1, *error_message);
    Handle<JSArray> array = factory->NewJSArrayWithElements(elements);
    Handle<Object> regexp_err =
        factory->NewSyntaxError("malformed_regexp", array);
    isolate->Throw(*regexp_err);
    return false;
  }
  
  
  bool RegExpImpl::CompileIrregexp(Handle<JSRegExp> re, bool is_ascii) {
    // Compile the RegExp.
    Isolate* isolate = re->GetIsolate();
    ZoneScope zone_scope(isolate, DELETE_ON_EXIT);
    PostponeInterruptsScope postpone(isolate);
    // If we had a compilation error the last time this is saved at the
    // saved code index.
    Object* entry = re->DataAt(JSRegExp::code_index(is_ascii));
    // When arriving here entry can only be a smi, either representing an
    // uncompiled regexp, a previous compilation error, or code that has
    // been flushed.
    ASSERT(entry->IsSmi());
    int entry_value = Smi::cast(entry)->value();
    ASSERT(entry_value == JSRegExp::kUninitializedValue ||
           entry_value == JSRegExp::kCompilationErrorValue ||
           (entry_value < JSRegExp::kCodeAgeMask && entry_value >= 0));
  
    if (entry_value == JSRegExp::kCompilationErrorValue) {
      // A previous compilation failed and threw an error which we store in
      // the saved code index (we store the error message, not the actual
      // error). Recreate the error object and throw it.
      Object* error_string = re->DataAt(JSRegExp::saved_code_index(is_ascii));
      ASSERT(error_string->IsString());
      Handle<String> error_message(String::cast(error_string));
      CreateRegExpErrorObjectAndThrow(re, is_ascii, error_message, isolate);
      return false;
    }
  
    JSRegExp::Flags flags = re->GetFlags();
  
    Handle<String> pattern(re->Pattern());
    if (!pattern->IsFlat()) FlattenString(pattern);
    RegExpCompileData compile_data;
    FlatStringReader reader(isolate, pattern);
    if (!RegExpParser::ParseRegExp(&reader, flags.is_multiline(),
                                   &compile_data)) {
      // Throw an exception if we fail to parse the pattern.
      // THIS SHOULD NOT HAPPEN. We already pre-parsed it successfully once.
      ThrowRegExpException(re,
                           pattern,
                           compile_data.error,
                           "malformed_regexp");
      return false;
    }
    RegExpEngine::CompilationResult result =
        RegExpEngine::Compile(&compile_data,
                              flags.is_ignore_case(),
                              flags.is_multiline(),
                              pattern,
                              is_ascii);
    if (result.error_message != NULL) {
      // Unable to compile regexp.
      Handle<String> error_message =
          isolate->factory()->NewStringFromUtf8(CStrVector(result.error_message));
      CreateRegExpErrorObjectAndThrow(re, is_ascii, error_message, isolate);
      return false;
    }
  
    Handle<FixedArray> data = Handle<FixedArray>(FixedArray::cast(re->data()));
    data->set(JSRegExp::code_index(is_ascii), result.code);
    int register_max = IrregexpMaxRegisterCount(*data);
    if (result.num_registers > register_max) {
      SetIrregexpMaxRegisterCount(*data, result.num_registers);
    }
  
    return true;
  }
  
  
  int RegExpImpl::IrregexpMaxRegisterCount(FixedArray* re) {
    return Smi::cast(
        re->get(JSRegExp::kIrregexpMaxRegisterCountIndex))->value();
  }
  
  
  void RegExpImpl::SetIrregexpMaxRegisterCount(FixedArray* re, int value) {
    re->set(JSRegExp::kIrregexpMaxRegisterCountIndex, Smi::FromInt(value));
  }
  
  
  int RegExpImpl::IrregexpNumberOfCaptures(FixedArray* re) {
    return Smi::cast(re->get(JSRegExp::kIrregexpCaptureCountIndex))->value();
  }
  
  
  int RegExpImpl::IrregexpNumberOfRegisters(FixedArray* re) {
    return Smi::cast(re->get(JSRegExp::kIrregexpMaxRegisterCountIndex))->value();
  }
  
  
  ByteArray* RegExpImpl::IrregexpByteCode(FixedArray* re, bool is_ascii) {
    return ByteArray::cast(re->get(JSRegExp::code_index(is_ascii)));
  }
  
  
  Code* RegExpImpl::IrregexpNativeCode(FixedArray* re, bool is_ascii) {
    return Code::cast(re->get(JSRegExp::code_index(is_ascii)));
  }
  
  
  void RegExpImpl::IrregexpInitialize(Handle<JSRegExp> re,
                                      Handle<String> pattern,
                                      JSRegExp::Flags flags,
                                      int capture_count) {
    // Initialize compiled code entries to null.
    re->GetIsolate()->factory()->SetRegExpIrregexpData(re,
                                                       JSRegExp::IRREGEXP,
                                                       pattern,
                                                       flags,
                                                       capture_count);
  }
  
  
  int RegExpImpl::IrregexpPrepare(Handle<JSRegExp> regexp,
                                  Handle<String> subject) {
    if (!subject->IsFlat()) FlattenString(subject);
  
    // Check the asciiness of the underlying storage.
    bool is_ascii = subject->IsAsciiRepresentationUnderneath();
    if (!EnsureCompiledIrregexp(regexp, is_ascii)) return -1;
  
  #ifdef V8_INTERPRETED_REGEXP
    // Byte-code regexp needs space allocated for all its registers.
    return IrregexpNumberOfRegisters(FixedArray::cast(regexp->data()));
  #else  // V8_INTERPRETED_REGEXP
    // Native regexp only needs room to output captures. Registers are handled
    // internally.
    return (IrregexpNumberOfCaptures(FixedArray::cast(regexp->data())) + 1) * 2;
  #endif  // V8_INTERPRETED_REGEXP
  }
  
  
  RegExpImpl::IrregexpResult RegExpImpl::IrregexpExecOnce(
      Handle<JSRegExp> regexp,
      Handle<String> subject,
      int index,
      Vector<int> output) {
    Isolate* isolate = regexp->GetIsolate();
  
    Handle<FixedArray> irregexp(FixedArray::cast(regexp->data()), isolate);
  
    ASSERT(index >= 0);
    ASSERT(index <= subject->length());
    ASSERT(subject->IsFlat());
  
    bool is_ascii = subject->IsAsciiRepresentationUnderneath();
  
  #ifndef V8_INTERPRETED_REGEXP
    ASSERT(output.length() >= (IrregexpNumberOfCaptures(*irregexp) + 1) * 2);
    do {
      EnsureCompiledIrregexp(regexp, is_ascii);
      Handle<Code> code(IrregexpNativeCode(*irregexp, is_ascii), isolate);
      NativeRegExpMacroAssembler::Result res =
          NativeRegExpMacroAssembler::Match(code,
                                            subject,
                                            output.start(),
                                            output.length(),
                                            index,
                                            isolate);
      if (res != NativeRegExpMacroAssembler::RETRY) {
        ASSERT(res != NativeRegExpMacroAssembler::EXCEPTION ||
               isolate->has_pending_exception());
        STATIC_ASSERT(
            static_cast<int>(NativeRegExpMacroAssembler::SUCCESS) == RE_SUCCESS);
        STATIC_ASSERT(
            static_cast<int>(NativeRegExpMacroAssembler::FAILURE) == RE_FAILURE);
        STATIC_ASSERT(static_cast<int>(NativeRegExpMacroAssembler::EXCEPTION)
                      == RE_EXCEPTION);
        return static_cast<IrregexpResult>(res);
      }
      // If result is RETRY, the string has changed representation, and we
      // must restart from scratch.
      // In this case, it means we must make sure we are prepared to handle
      // the, potentially, different subject (the string can switch between
      // being internal and external, and even between being ASCII and UC16,
      // but the characters are always the same).
      IrregexpPrepare(regexp, subject);
      is_ascii = subject->IsAsciiRepresentationUnderneath();
    } while (true);
    UNREACHABLE();
    return RE_EXCEPTION;
  #else  // V8_INTERPRETED_REGEXP
  
    ASSERT(output.length() >= IrregexpNumberOfRegisters(*irregexp));
    // We must have done EnsureCompiledIrregexp, so we can get the number of
    // registers.
    int* register_vector = output.start();
    int number_of_capture_registers =
        (IrregexpNumberOfCaptures(*irregexp) + 1) * 2;
    for (int i = number_of_capture_registers - 1; i >= 0; i--) {
      register_vector[i] = -1;
    }
    Handle<ByteArray> byte_codes(IrregexpByteCode(*irregexp, is_ascii), isolate);
  
    IrregexpResult result = IrregexpInterpreter::Match(isolate,
                                                       byte_codes,
                                                       subject,
                                                       register_vector,
                                                       index);
    if (result == RE_EXCEPTION) {
      ASSERT(!isolate->has_pending_exception());
      isolate->StackOverflow();
    }
    return result;
  #endif  // V8_INTERPRETED_REGEXP
  }
  
  
  Handle<Object> RegExpImpl::IrregexpExec(Handle<JSRegExp> jsregexp,
                                          Handle<String> subject,
                                          int previous_index,
                                          Handle<JSArray> last_match_info) {
    ASSERT_EQ(jsregexp->TypeTag(), JSRegExp::IRREGEXP);
  
    // Prepare space for the return values.
  #ifdef V8_INTERPRETED_REGEXP
  #ifdef DEBUG
    if (FLAG_trace_regexp_bytecodes) {
      String* pattern = jsregexp->Pattern();
      PrintF("\n\nRegexp match:   /%s/\n\n", *(pattern->ToCString()));
      PrintF("\n\nSubject string: '%s'\n\n", *(subject->ToCString()));
    }
  #endif
  #endif
    int required_registers = RegExpImpl::IrregexpPrepare(jsregexp, subject);
    if (required_registers < 0) {
      // Compiling failed with an exception.
      ASSERT(Isolate::Current()->has_pending_exception());
      return Handle<Object>::null();
    }
  
    OffsetsVector registers(required_registers);
  
    IrregexpResult res = RegExpImpl::IrregexpExecOnce(
        jsregexp, subject, previous_index, Vector<int>(registers.vector(),
                                                       registers.length()));
    if (res == RE_SUCCESS) {
      int capture_register_count =
          (IrregexpNumberOfCaptures(FixedArray::cast(jsregexp->data())) + 1) * 2;
      last_match_info->EnsureSize(capture_register_count + kLastMatchOverhead);
      AssertNoAllocation no_gc;
      int* register_vector = registers.vector();
      FixedArray* array = FixedArray::cast(last_match_info->elements());
      for (int i = 0; i < capture_register_count; i += 2) {
        SetCapture(array, i, register_vector[i]);
        SetCapture(array, i + 1, register_vector[i + 1]);
      }
      SetLastCaptureCount(array, capture_register_count);
      SetLastSubject(array, *subject);
      SetLastInput(array, *subject);
      return last_match_info;
    }
    if (res == RE_EXCEPTION) {
      ASSERT(Isolate::Current()->has_pending_exception());
      return Handle<Object>::null();
    }
    ASSERT(res == RE_FAILURE);
    return Isolate::Current()->factory()->null_value();
  }
  
  
  // -------------------------------------------------------------------
  // Implementation of the Irregexp regular expression engine.
  //
  // The Irregexp regular expression engine is intended to be a complete
  // implementation of ECMAScript regular expressions.  It generates either
  // bytecodes or native code.
  
  //   The Irregexp regexp engine is structured in three steps.
  //   1) The parser generates an abstract syntax tree.  See ast.cc.
  //   2) From the AST a node network is created.  The nodes are all
  //      subclasses of RegExpNode.  The nodes represent states when
  //      executing a regular expression.  Several optimizations are
  //      performed on the node network.
  //   3) From the nodes we generate either byte codes or native code
  //      that can actually execute the regular expression (perform
  //      the search).  The code generation step is described in more
  //      detail below.
  
  // Code generation.
  //
  //   The nodes are divided into four main categories.
  //   * Choice nodes
  //        These represent places where the regular expression can
  //        match in more than one way.  For example on entry to an
  //        alternation (foo|bar) or a repetition (*, +, ? or {}).
  //   * Action nodes
  //        These represent places where some action should be
  //        performed.  Examples include recording the current position
  //        in the input string to a register (in order to implement
  //        captures) or other actions on register for example in order
  //        to implement the counters needed for {} repetitions.
  //   * Matching nodes
  //        These attempt to match some element part of the input string.
  //        Examples of elements include character classes, plain strings
  //        or back references.
  //   * End nodes
  //        These are used to implement the actions required on finding
  //        a successful match or failing to find a match.
  //
  //   The code generated (whether as byte codes or native code) maintains
  //   some state as it runs.  This consists of the following elements:
  //
  //   * The capture registers.  Used for string captures.
  //   * Other registers.  Used for counters etc.
  //   * The current position.
  //   * The stack of backtracking information.  Used when a matching node
  //     fails to find a match and needs to try an alternative.
  //
  // Conceptual regular expression execution model:
  //
  //   There is a simple conceptual model of regular expression execution
  //   which will be presented first.  The actual code generated is a more
  //   efficient simulation of the simple conceptual model:
  //
  //   * Choice nodes are implemented as follows:
  //     For each choice except the last {
  //       push current position
  //       push backtrack code location
  //       <generate code to test for choice>
  //       backtrack code location:
  //       pop current position
  //     }
  //     <generate code to test for last choice>
  //
  //   * Actions nodes are generated as follows
  //     <push affected registers on backtrack stack>
  //     <generate code to perform action>
  //     push backtrack code location
  //     <generate code to test for following nodes>
  //     backtrack code location:
  //     <pop affected registers to restore their state>
  //     <pop backtrack location from stack and go to it>
  //
  //   * Matching nodes are generated as follows:
  //     if input string matches at current position
  //       update current position
  //       <generate code to test for following nodes>
  //     else
  //       <pop backtrack location from stack and go to it>
  //
  //   Thus it can be seen that the current position is saved and restored
  //   by the choice nodes, whereas the registers are saved and restored by
  //   by the action nodes that manipulate them.
  //
  //   The other interesting aspect of this model is that nodes are generated
  //   at the point where they are needed by a recursive call to Emit().  If
  //   the node has already been code generated then the Emit() call will
  //   generate a jump to the previously generated code instead.  In order to
  //   limit recursion it is possible for the Emit() function to put the node
  //   on a work list for later generation and instead generate a jump.  The
  //   destination of the jump is resolved later when the code is generated.
  //
  // Actual regular expression code generation.
  //
  //   Code generation is actually more complicated than the above.  In order
  //   to improve the efficiency of the generated code some optimizations are
  //   performed
  //
  //   * Choice nodes have 1-character lookahead.
  //     A choice node looks at the following character and eliminates some of
  //     the choices immediately based on that character.  This is not yet
  //     implemented.
  //   * Simple greedy loops store reduced backtracking information.
  //     A quantifier like /.*foo/m will greedily match the whole input.  It will
  //     then need to backtrack to a point where it can match "foo".  The naive
  //     implementation of this would push each character position onto the
  //     backtracking stack, then pop them off one by one.  This would use space
  //     proportional to the length of the input string.  However since the "."
  //     can only match in one way and always has a constant length (in this case
  //     of 1) it suffices to store the current position on the top of the stack
  //     once.  Matching now becomes merely incrementing the current position and
  //     backtracking becomes decrementing the current position and checking the
  //     result against the stored current position.  This is faster and saves
  //     space.
  //   * The current state is virtualized.
  //     This is used to defer expensive operations until it is clear that they
  //     are needed and to generate code for a node more than once, allowing
  //     specialized an efficient versions of the code to be created. This is
  //     explained in the section below.
  //
  // Execution state virtualization.
  //
  //   Instead of emitting code, nodes that manipulate the state can record their
  //   manipulation in an object called the Trace.  The Trace object can record a
  //   current position offset, an optional backtrack code location on the top of
  //   the virtualized backtrack stack and some register changes.  When a node is
  //   to be emitted it can flush the Trace or update it.  Flushing the Trace
  //   will emit code to bring the actual state into line with the virtual state.
  //   Avoiding flushing the state can postpone some work (e.g. updates of capture
  //   registers).  Postponing work can save time when executing the regular
  //   expression since it may be found that the work never has to be done as a
  //   failure to match can occur.  In addition it is much faster to jump to a
  //   known backtrack code location than it is to pop an unknown backtrack
  //   location from the stack and jump there.
  //
  //   The virtual state found in the Trace affects code generation.  For example
  //   the virtual state contains the difference between the actual current
  //   position and the virtual current position, and matching code needs to use
  //   this offset to attempt a match in the correct location of the input
  //   string.  Therefore code generated for a non-trivial trace is specialized
  //   to that trace.  The code generator therefore has the ability to generate
  //   code for each node several times.  In order to limit the size of the
  //   generated code there is an arbitrary limit on how many specialized sets of
  //   code may be generated for a given node.  If the limit is reached, the
  //   trace is flushed and a generic version of the code for a node is emitted.
  //   This is subsequently used for that node.  The code emitted for non-generic
  //   trace is not recorded in the node and so it cannot currently be reused in
  //   the event that code generation is requested for an identical trace.
  
  
  void RegExpTree::AppendToText(RegExpText* text) {
    UNREACHABLE();
  }
  
  
  void RegExpAtom::AppendToText(RegExpText* text) {
    text->AddElement(TextElement::Atom(this));
  }
  
  
  void RegExpCharacterClass::AppendToText(RegExpText* text) {
    text->AddElement(TextElement::CharClass(this));
  }
  
  
  void RegExpText::AppendToText(RegExpText* text) {
    for (int i = 0; i < elements()->length(); i++)
      text->AddElement(elements()->at(i));
  }
  
  
  TextElement TextElement::Atom(RegExpAtom* atom) {
    TextElement result = TextElement(ATOM);
    result.data.u_atom = atom;
    return result;
  }
  
  
  TextElement TextElement::CharClass(
        RegExpCharacterClass* char_class) {
    TextElement result = TextElement(CHAR_CLASS);
    result.data.u_char_class = char_class;
    return result;
  }
  
  
  int TextElement::length() {
    if (type == ATOM) {
      return data.u_atom->length();
    } else {
      ASSERT(type == CHAR_CLASS);
      return 1;
    }
  }
  
  
  DispatchTable* ChoiceNode::GetTable(bool ignore_case) {
    if (table_ == NULL) {
      table_ = new DispatchTable();
      DispatchTableConstructor cons(table_, ignore_case);
      cons.BuildTable(this);
    }
    return table_;
  }
  
  
  class RegExpCompiler {
   public:
    RegExpCompiler(int capture_count, bool ignore_case, bool is_ascii);
  
    int AllocateRegister() {
      if (next_register_ >= RegExpMacroAssembler::kMaxRegister) {
        reg_exp_too_big_ = true;
        return next_register_;
      }
      return next_register_++;
    }
  
    RegExpEngine::CompilationResult Assemble(RegExpMacroAssembler* assembler,
                                             RegExpNode* start,
                                             int capture_count,
                                             Handle<String> pattern);
  
    inline void AddWork(RegExpNode* node) { work_list_->Add(node); }
  
    static const int kImplementationOffset = 0;
    static const int kNumberOfRegistersOffset = 0;
    static const int kCodeOffset = 1;
  
    RegExpMacroAssembler* macro_assembler() { return macro_assembler_; }
    EndNode* accept() { return accept_; }
  
    static const int kMaxRecursion = 100;
    inline int recursion_depth() { return recursion_depth_; }
    inline void IncrementRecursionDepth() { recursion_depth_++; }
    inline void DecrementRecursionDepth() { recursion_depth_--; }
  
    void SetRegExpTooBig() { reg_exp_too_big_ = true; }
  
    inline bool ignore_case() { return ignore_case_; }
    inline bool ascii() { return ascii_; }
  
    int current_expansion_factor() { return current_expansion_factor_; }
    void set_current_expansion_factor(int value) {
      current_expansion_factor_ = value;
    }
  
    static const int kNoRegister = -1;
  
   private:
    EndNode* accept_;
    int next_register_;
    List<RegExpNode*>* work_list_;
    int recursion_depth_;
    RegExpMacroAssembler* macro_assembler_;
    bool ignore_case_;
    bool ascii_;
    bool reg_exp_too_big_;
    int current_expansion_factor_;
  };
  
  
  class RecursionCheck {
   public:
    explicit RecursionCheck(RegExpCompiler* compiler) : compiler_(compiler) {
      compiler->IncrementRecursionDepth();
    }
    ~RecursionCheck() { compiler_->DecrementRecursionDepth(); }
   private:
    RegExpCompiler* compiler_;
  };
  
  
  static RegExpEngine::CompilationResult IrregexpRegExpTooBig() {
    return RegExpEngine::CompilationResult("RegExp too big");
  }
  
  
  // Attempts to compile the regexp using an Irregexp code generator.  Returns
  // a fixed array or a null handle depending on whether it succeeded.
  RegExpCompiler::RegExpCompiler(int capture_count, bool ignore_case, bool ascii)
      : next_register_(2 * (capture_count + 1)),
        work_list_(NULL),
        recursion_depth_(0),
        ignore_case_(ignore_case),
        ascii_(ascii),
        reg_exp_too_big_(false),
        current_expansion_factor_(1) {
    accept_ = new EndNode(EndNode::ACCEPT);
    ASSERT(next_register_ - 1 <= RegExpMacroAssembler::kMaxRegister);
  }
  
  
  RegExpEngine::CompilationResult RegExpCompiler::Assemble(
      RegExpMacroAssembler* macro_assembler,
      RegExpNode* start,
      int capture_count,
      Handle<String> pattern) {
    Heap* heap = pattern->GetHeap();
  
    bool use_slow_safe_regexp_compiler = false;
    if (heap->total_regexp_code_generated() >
            RegExpImpl::kRegWxpCompiledLimit &&
        heap->isolate()->memory_allocator()->SizeExecutable() >
            RegExpImpl::kRegExpExecutableMemoryLimit) {
      use_slow_safe_regexp_compiler = true;
    }
  
    macro_assembler->set_slow_safe(use_slow_safe_regexp_compiler);
  
  #ifdef DEBUG
    if (FLAG_trace_regexp_assembler)
      macro_assembler_ = new RegExpMacroAssemblerTracer(macro_assembler);
    else
  #endif
      macro_assembler_ = macro_assembler;
  
    List <RegExpNode*> work_list(0);
    work_list_ = &work_list;
    Label fail;
    macro_assembler_->PushBacktrack(&fail);
    Trace new_trace;
    start->Emit(this, &new_trace);
    macro_assembler_->Bind(&fail);
    macro_assembler_->Fail();
    while (!work_list.is_empty()) {
      work_list.RemoveLast()->Emit(this, &new_trace);
    }
    if (reg_exp_too_big_) return IrregexpRegExpTooBig();
  
    Handle<HeapObject> code = macro_assembler_->GetCode(pattern);
    heap->IncreaseTotalRegexpCodeGenerated(code->Size());
    work_list_ = NULL;
  #ifdef DEBUG
    if (FLAG_print_code) {
      Handle<Code>::cast(code)->Disassemble(*pattern->ToCString());
    }
    if (FLAG_trace_regexp_assembler) {
      delete macro_assembler_;
    }
  #endif
    return RegExpEngine::CompilationResult(*code, next_register_);
  }
  
  
  bool Trace::DeferredAction::Mentions(int that) {
    if (type() == ActionNode::CLEAR_CAPTURES) {
      Interval range = static_cast<DeferredClearCaptures*>(this)->range();
      return range.Contains(that);
    } else {
      return reg() == that;
    }
  }
  
  
  bool Trace::mentions_reg(int reg) {
    for (DeferredAction* action = actions_;
         action != NULL;
         action = action->next()) {
      if (action->Mentions(reg))
        return true;
    }
    return false;
  }
  
  
  bool Trace::GetStoredPosition(int reg, int* cp_offset) {
    ASSERT_EQ(0, *cp_offset);
    for (DeferredAction* action = actions_;
         action != NULL;
         action = action->next()) {
      if (action->Mentions(reg)) {
        if (action->type() == ActionNode::STORE_POSITION) {
          *cp_offset = static_cast<DeferredCapture*>(action)->cp_offset();
          return true;
        } else {
          return false;
        }
      }
    }
    return false;
  }
  
  
  int Trace::FindAffectedRegisters(OutSet* affected_registers) {
    int max_register = RegExpCompiler::kNoRegister;
    for (DeferredAction* action = actions_;
         action != NULL;
         action = action->next()) {
      if (action->type() == ActionNode::CLEAR_CAPTURES) {
        Interval range = static_cast<DeferredClearCaptures*>(action)->range();
        for (int i = range.from(); i <= range.to(); i++)
          affected_registers->Set(i);
        if (range.to() > max_register) max_register = range.to();
      } else {
        affected_registers->Set(action->reg());
        if (action->reg() > max_register) max_register = action->reg();
      }
    }
    return max_register;
  }
  
  
  void Trace::RestoreAffectedRegisters(RegExpMacroAssembler* assembler,
                                       int max_register,
                                       OutSet& registers_to_pop,
                                       OutSet& registers_to_clear) {
    for (int reg = max_register; reg >= 0; reg--) {
      if (registers_to_pop.Get(reg)) assembler->PopRegister(reg);
      else if (registers_to_clear.Get(reg)) {
        int clear_to = reg;
        while (reg > 0 && registers_to_clear.Get(reg - 1)) {
          reg--;
        }
        assembler->ClearRegisters(reg, clear_to);
      }
    }
  }
  
  
  void Trace::PerformDeferredActions(RegExpMacroAssembler* assembler,
                                     int max_register,
                                     OutSet& affected_registers,
                                     OutSet* registers_to_pop,
                                     OutSet* registers_to_clear) {
    // The "+1" is to avoid a push_limit of zero if stack_limit_slack() is 1.
    const int push_limit = (assembler->stack_limit_slack() + 1) / 2;
  
    // Count pushes performed to force a stack limit check occasionally.
    int pushes = 0;
  
    for (int reg = 0; reg <= max_register; reg++) {
      if (!affected_registers.Get(reg)) {
        continue;
      }
  
      // The chronologically first deferred action in the trace
      // is used to infer the action needed to restore a register
      // to its previous state (or not, if it's safe to ignore it).
      enum DeferredActionUndoType { IGNORE, RESTORE, CLEAR };
      DeferredActionUndoType undo_action = IGNORE;
  
      int value = 0;
      bool absolute = false;
      bool clear = false;
      int store_position = -1;
      // This is a little tricky because we are scanning the actions in reverse
      // historical order (newest first).
      for (DeferredAction* action = actions_;
           action != NULL;
           action = action->next()) {
        if (action->Mentions(reg)) {
          switch (action->type()) {
            case ActionNode::SET_REGISTER: {
              Trace::DeferredSetRegister* psr =
                  static_cast<Trace::DeferredSetRegister*>(action);
              if (!absolute) {
                value += psr->value();
                absolute = true;
              }
              // SET_REGISTER is currently only used for newly introduced loop
              // counters. They can have a significant previous value if they
              // occour in a loop. TODO(lrn): Propagate this information, so
              // we can set undo_action to IGNORE if we know there is no value to
              // restore.
              undo_action = RESTORE;
              ASSERT_EQ(store_position, -1);
              ASSERT(!clear);
              break;
            }
            case ActionNode::INCREMENT_REGISTER:
              if (!absolute) {
                value++;
              }
              ASSERT_EQ(store_position, -1);
              ASSERT(!clear);
              undo_action = RESTORE;
              break;
            case ActionNode::STORE_POSITION: {
              Trace::DeferredCapture* pc =
                  static_cast<Trace::DeferredCapture*>(action);
              if (!clear && store_position == -1) {
                store_position = pc->cp_offset();
              }
  
              // For captures we know that stores and clears alternate.
              // Other register, are never cleared, and if the occur
              // inside a loop, they might be assigned more than once.
              if (reg <= 1) {
                // Registers zero and one, aka "capture zero", is
                // always set correctly if we succeed. There is no
                // need to undo a setting on backtrack, because we
                // will set it again or fail.
                undo_action = IGNORE;
              } else {
                undo_action = pc->is_capture() ? CLEAR : RESTORE;
              }
              ASSERT(!absolute);
              ASSERT_EQ(value, 0);
              break;
            }
            case ActionNode::CLEAR_CAPTURES: {
              // Since we're scanning in reverse order, if we've already
              // set the position we have to ignore historically earlier
              // clearing operations.
              if (store_position == -1) {
                clear = true;
              }
              undo_action = RESTORE;
              ASSERT(!absolute);
              ASSERT_EQ(value, 0);
              break;
            }
            default:
              UNREACHABLE();
              break;
          }
        }
      }
      // Prepare for the undo-action (e.g., push if it's going to be popped).
      if (undo_action == RESTORE) {
        pushes++;
        RegExpMacroAssembler::StackCheckFlag stack_check =
            RegExpMacroAssembler::kNoStackLimitCheck;
        if (pushes == push_limit) {
          stack_check = RegExpMacroAssembler::kCheckStackLimit;
          pushes = 0;
        }
  
        assembler->PushRegister(reg, stack_check);
        registers_to_pop->Set(reg);
      } else if (undo_action == CLEAR) {
        registers_to_clear->Set(reg);
      }
      // Perform the chronologically last action (or accumulated increment)
      // for the register.
      if (store_position != -1) {
        assembler->WriteCurrentPositionToRegister(reg, store_position);
      } else if (clear) {
        assembler->ClearRegisters(reg, reg);
      } else if (absolute) {
        assembler->SetRegister(reg, value);
      } else if (value != 0) {
        assembler->AdvanceRegister(reg, value);
      }
    }
  }
  
  
  // This is called as we come into a loop choice node and some other tricky
  // nodes.  It normalizes the state of the code generator to ensure we can
  // generate generic code.
  void Trace::Flush(RegExpCompiler* compiler, RegExpNode* successor) {
    RegExpMacroAssembler* assembler = compiler->macro_assembler();
  
    ASSERT(!is_trivial());
  
    if (actions_ == NULL && backtrack() == NULL) {
      // Here we just have some deferred cp advances to fix and we are back to
      // a normal situation.  We may also have to forget some information gained
      // through a quick check that was already performed.
      if (cp_offset_ != 0) assembler->AdvanceCurrentPosition(cp_offset_);
      // Create a new trivial state and generate the node with that.
      Trace new_state;
      successor->Emit(compiler, &new_state);
      return;
    }
  
    // Generate deferred actions here along with code to undo them again.
    OutSet affected_registers;
  
    if (backtrack() != NULL) {
      // Here we have a concrete backtrack location.  These are set up by choice
      // nodes and so they indicate that we have a deferred save of the current
      // position which we may need to emit here.
      assembler->PushCurrentPosition();
    }
  
    int max_register = FindAffectedRegisters(&affected_registers);
    OutSet registers_to_pop;
    OutSet registers_to_clear;
    PerformDeferredActions(assembler,
                           max_register,
                           affected_registers,
                           &registers_to_pop,
                           &registers_to_clear);
    if (cp_offset_ != 0) {
      assembler->AdvanceCurrentPosition(cp_offset_);
    }
  
    // Create a new trivial state and generate the node with that.
    Label undo;
    assembler->PushBacktrack(&undo);
    Trace new_state;
    successor->Emit(compiler, &new_state);
  
    // On backtrack we need to restore state.
    assembler->Bind(&undo);
    RestoreAffectedRegisters(assembler,
                             max_register,
                             registers_to_pop,
                             registers_to_clear);
    if (backtrack() == NULL) {
      assembler->Backtrack();
    } else {
      assembler->PopCurrentPosition();
      assembler->GoTo(backtrack());
    }
  }
  
  
  void NegativeSubmatchSuccess::Emit(RegExpCompiler* compiler, Trace* trace) {
    RegExpMacroAssembler* assembler = compiler->macro_assembler();
  
    // Omit flushing the trace. We discard the entire stack frame anyway.
  
    if (!label()->is_bound()) {
      // We are completely independent of the trace, since we ignore it,
      // so this code can be used as the generic version.
      assembler->Bind(label());
    }
  
    // Throw away everything on the backtrack stack since the start
    // of the negative submatch and restore the character position.
    assembler->ReadCurrentPositionFromRegister(current_position_register_);
    assembler->ReadStackPointerFromRegister(stack_pointer_register_);
    if (clear_capture_count_ > 0) {
      // Clear any captures that might have been performed during the success
      // of the body of the negative look-ahead.
      int clear_capture_end = clear_capture_start_ + clear_capture_count_ - 1;
      assembler->ClearRegisters(clear_capture_start_, clear_capture_end);
    }
    // Now that we have unwound the stack we find at the top of the stack the
    // backtrack that the BeginSubmatch node got.
    assembler->Backtrack();
  }
  
  
  void EndNode::Emit(RegExpCompiler* compiler, Trace* trace) {
    if (!trace->is_trivial()) {
      trace->Flush(compiler, this);
      return;
    }
    RegExpMacroAssembler* assembler = compiler->macro_assembler();
    if (!label()->is_bound()) {
      assembler->Bind(label());
    }
    switch (action_) {
      case ACCEPT:
        assembler->Succeed();
        return;
      case BACKTRACK:
        assembler->GoTo(trace->backtrack());
        return;
      case NEGATIVE_SUBMATCH_SUCCESS:
        // This case is handled in a different virtual method.
        UNREACHABLE();
    }
    UNIMPLEMENTED();
  }
  
  
  void GuardedAlternative::AddGuard(Guard* guard) {
    if (guards_ == NULL)
      guards_ = new ZoneList<Guard*>(1);
    guards_->Add(guard);
  }
  
  
  ActionNode* ActionNode::SetRegister(int reg,
                                      int val,
                                      RegExpNode* on_success) {
    ActionNode* result = new ActionNode(SET_REGISTER, on_success);
    result->data_.u_store_register.reg = reg;
    result->data_.u_store_register.value = val;
    return result;
  }
  
  
  ActionNode* ActionNode::IncrementRegister(int reg, RegExpNode* on_success) {
    ActionNode* result = new ActionNode(INCREMENT_REGISTER, on_success);
    result->data_.u_increment_register.reg = reg;
    return result;
  }
  
  
  ActionNode* ActionNode::StorePosition(int reg,
                                        bool is_capture,
                                        RegExpNode* on_success) {
    ActionNode* result = new ActionNode(STORE_POSITION, on_success);
    result->data_.u_position_register.reg = reg;
    result->data_.u_position_register.is_capture = is_capture;
    return result;
  }
  
  
  ActionNode* ActionNode::ClearCaptures(Interval range,
                                        RegExpNode* on_success) {
    ActionNode* result = new ActionNode(CLEAR_CAPTURES, on_success);
    result->data_.u_clear_captures.range_from = range.from();
    result->data_.u_clear_captures.range_to = range.to();
    return result;
  }
  
  
  ActionNode* ActionNode::BeginSubmatch(int stack_reg,
                                        int position_reg,
                                        RegExpNode* on_success) {
    ActionNode* result = new ActionNode(BEGIN_SUBMATCH, on_success);
    result->data_.u_submatch.stack_pointer_register = stack_reg;
    result->data_.u_submatch.current_position_register = position_reg;
    return result;
  }
  
  
  ActionNode* ActionNode::PositiveSubmatchSuccess(int stack_reg,
                                                  int position_reg,
                                                  int clear_register_count,
                                                  int clear_register_from,
                                                  RegExpNode* on_success) {
    ActionNode* result = new ActionNode(POSITIVE_SUBMATCH_SUCCESS, on_success);
    result->data_.u_submatch.stack_pointer_register = stack_reg;
    result->data_.u_submatch.current_position_register = position_reg;
    result->data_.u_submatch.clear_register_count = clear_register_count;
    result->data_.u_submatch.clear_register_from = clear_register_from;
    return result;
  }
  
  
  ActionNode* ActionNode::EmptyMatchCheck(int start_register,
                                          int repetition_register,
                                          int repetition_limit,
                                          RegExpNode* on_success) {
    ActionNode* result = new ActionNode(EMPTY_MATCH_CHECK, on_success);
    result->data_.u_empty_match_check.start_register = start_register;
    result->data_.u_empty_match_check.repetition_register = repetition_register;
    result->data_.u_empty_match_check.repetition_limit = repetition_limit;
    return result;
  }
  
  
  #define DEFINE_ACCEPT(Type)                                          \
    void Type##Node::Accept(NodeVisitor* visitor) {                    \
      visitor->Visit##Type(this);                                      \
    }
  FOR_EACH_NODE_TYPE(DEFINE_ACCEPT)
  #undef DEFINE_ACCEPT
  
  
  void LoopChoiceNode::Accept(NodeVisitor* visitor) {
    visitor->VisitLoopChoice(this);
  }
  
  
  // -------------------------------------------------------------------
  // Emit code.
  
  
  void ChoiceNode::GenerateGuard(RegExpMacroAssembler* macro_assembler,
                                 Guard* guard,
                                 Trace* trace) {
    switch (guard->op()) {
      case Guard::LT:
        ASSERT(!trace->mentions_reg(guard->reg()));
        macro_assembler->IfRegisterGE(guard->reg(),
                                      guard->value(),
                                      trace->backtrack());
        break;
      case Guard::GEQ:
        ASSERT(!trace->mentions_reg(guard->reg()));
        macro_assembler->IfRegisterLT(guard->reg(),
                                      guard->value(),
                                      trace->backtrack());
        break;
    }
  }
  
  
  // Returns the number of characters in the equivalence class, omitting those
  // that cannot occur in the source string because it is ASCII.
  static int GetCaseIndependentLetters(Isolate* isolate,
                                       uc16 character,
                                       bool ascii_subject,
                                       unibrow::uchar* letters) {
    int length =
        isolate->jsregexp_uncanonicalize()->get(character, '\0', letters);
    // Unibrow returns 0 or 1 for characters where case independence is
    // trivial.
    if (length == 0) {
      letters[0] = character;
      length = 1;
    }
    if (!ascii_subject || character <= String::kMaxAsciiCharCode) {
      return length;
    }
    // The standard requires that non-ASCII characters cannot have ASCII
    // character codes in their equivalence class.
    return 0;
  }
  
  
  static inline bool EmitSimpleCharacter(Isolate* isolate,
                                         RegExpCompiler* compiler,
                                         uc16 c,
                                         Label* on_failure,
                                         int cp_offset,
                                         bool check,
                                         bool preloaded) {
    RegExpMacroAssembler* assembler = compiler->macro_assembler();
    bool bound_checked = false;
    if (!preloaded) {
      assembler->LoadCurrentCharacter(
          cp_offset,
          on_failure,
          check);
      bound_checked = true;
    }
    assembler->CheckNotCharacter(c, on_failure);
    return bound_checked;
  }
  
  
  // Only emits non-letters (things that don't have case).  Only used for case
  // independent matches.
  static inline bool EmitAtomNonLetter(Isolate* isolate,
                                       RegExpCompiler* compiler,
                                       uc16 c,
                                       Label* on_failure,
                                       int cp_offset,
                                       bool check,
                                       bool preloaded) {
    RegExpMacroAssembler* macro_assembler = compiler->macro_assembler();
    bool ascii = compiler->ascii();
    unibrow::uchar chars[unibrow::Ecma262UnCanonicalize::kMaxWidth];
    int length = GetCaseIndependentLetters(isolate, c, ascii, chars);
    if (length < 1) {
      // This can't match.  Must be an ASCII subject and a non-ASCII character.
      // We do not need to do anything since the ASCII pass already handled this.
      return false;  // Bounds not checked.
    }
    bool checked = false;
    // We handle the length > 1 case in a later pass.
    if (length == 1) {
      if (ascii && c > String::kMaxAsciiCharCodeU) {
        // Can't match - see above.
        return false;  // Bounds not checked.
      }
      if (!preloaded) {
        macro_assembler->LoadCurrentCharacter(cp_offset, on_failure, check);
        checked = check;
      }
      macro_assembler->CheckNotCharacter(c, on_failure);
    }
    return checked;
  }
  
  
  static bool ShortCutEmitCharacterPair(RegExpMacroAssembler* macro_assembler,
                                        bool ascii,
                                        uc16 c1,
                                        uc16 c2,
                                        Label* on_failure) {
    uc16 char_mask;
    if (ascii) {
      char_mask = String::kMaxAsciiCharCode;
    } else {
      char_mask = String::kMaxUC16CharCode;
    }
    uc16 exor = c1 ^ c2;
    // Check whether exor has only one bit set.
    if (((exor - 1) & exor) == 0) {
      // If c1 and c2 differ only by one bit.
      // Ecma262UnCanonicalize always gives the highest number last.
      ASSERT(c2 > c1);
      uc16 mask = char_mask ^ exor;
      macro_assembler->CheckNotCharacterAfterAnd(c1, mask, on_failure);
      return true;
    }
    ASSERT(c2 > c1);
    uc16 diff = c2 - c1;
    if (((diff - 1) & diff) == 0 && c1 >= diff) {
      // If the characters differ by 2^n but don't differ by one bit then
      // subtract the difference from the found character, then do the or
      // trick.  We avoid the theoretical case where negative numbers are
      // involved in order to simplify code generation.
      uc16 mask = char_mask ^ diff;
      macro_assembler->CheckNotCharacterAfterMinusAnd(c1 - diff,
                                                      diff,
                                                      mask,
                                                      on_failure);
      return true;
    }
    return false;
  }
  
  
  typedef bool EmitCharacterFunction(Isolate* isolate,
                                     RegExpCompiler* compiler,
                                     uc16 c,
                                     Label* on_failure,
                                     int cp_offset,
                                     bool check,
                                     bool preloaded);
  
  // Only emits letters (things that have case).  Only used for case independent
  // matches.
  static inline bool EmitAtomLetter(Isolate* isolate,
                                    RegExpCompiler* compiler,
                                    uc16 c,
                                    Label* on_failure,
                                    int cp_offset,
                                    bool check,
                                    bool preloaded) {
    RegExpMacroAssembler* macro_assembler = compiler->macro_assembler();
    bool ascii = compiler->ascii();
    unibrow::uchar chars[unibrow::Ecma262UnCanonicalize::kMaxWidth];
    int length = GetCaseIndependentLetters(isolate, c, ascii, chars);
    if (length <= 1) return false;
    // We may not need to check against the end of the input string
    // if this character lies before a character that matched.
    if (!preloaded) {
      macro_assembler->LoadCurrentCharacter(cp_offset, on_failure, check);
    }
    Label ok;
    ASSERT(unibrow::Ecma262UnCanonicalize::kMaxWidth == 4);
    switch (length) {
      case 2: {
        if (ShortCutEmitCharacterPair(macro_assembler,
                                      ascii,
                                      chars[0],
                                      chars[1],
                                      on_failure)) {
        } else {
          macro_assembler->CheckCharacter(chars[0], &ok);
          macro_assembler->CheckNotCharacter(chars[1], on_failure);
          macro_assembler->Bind(&ok);
        }
        break;
      }
      case 4:
        macro_assembler->CheckCharacter(chars[3], &ok);
        // Fall through!
      case 3:
        macro_assembler->CheckCharacter(chars[0], &ok);
        macro_assembler->CheckCharacter(chars[1], &ok);
        macro_assembler->CheckNotCharacter(chars[2], on_failure);
        macro_assembler->Bind(&ok);
        break;
      default:
        UNREACHABLE();
        break;
    }
    return true;
  }
  
  
  static void EmitCharClass(RegExpMacroAssembler* macro_assembler,
                            RegExpCharacterClass* cc,
                            bool ascii,
                            Label* on_failure,
                            int cp_offset,
                            bool check_offset,
                            bool preloaded) {
    ZoneList<CharacterRange>* ranges = cc->ranges();
    int max_char;
    if (ascii) {
      max_char = String::kMaxAsciiCharCode;
    } else {
      max_char = String::kMaxUC16CharCode;
    }
  
    Label success;
  
    Label* char_is_in_class =
        cc->is_negated() ? on_failure : &success;
  
    int range_count = ranges->length();
  
    int last_valid_range = range_count - 1;
    while (last_valid_range >= 0) {
      CharacterRange& range = ranges->at(last_valid_range);
      if (range.from() <= max_char) {
        break;
      }
      last_valid_range--;
    }
  
    if (last_valid_range < 0) {
      if (!cc->is_negated()) {
        // TODO(plesner): We can remove this when the node level does our
        // ASCII optimizations for us.
        macro_assembler->GoTo(on_failure);
      }
      if (check_offset) {
        macro_assembler->CheckPosition(cp_offset, on_failure);
      }
      return;
    }
  
    if (last_valid_range == 0 &&
        !cc->is_negated() &&
        ranges->at(0).IsEverything(max_char)) {
      // This is a common case hit by non-anchored expressions.
      if (check_offset) {
        macro_assembler->CheckPosition(cp_offset, on_failure);
      }
      return;
    }
  
    if (!preloaded) {
      macro_assembler->LoadCurrentCharacter(cp_offset, on_failure, check_offset);
    }
  
    if (cc->is_standard() &&
          macro_assembler->CheckSpecialCharacterClass(cc->standard_type(),
                                                      on_failure)) {
        return;
    }
  
    for (int i = 0; i < last_valid_range; i++) {
      CharacterRange& range = ranges->at(i);
      Label next_range;
      uc16 from = range.from();
      uc16 to = range.to();
      if (from > max_char) {
        continue;
      }
      if (to > max_char) to = max_char;
      if (to == from) {
        macro_assembler->CheckCharacter(to, char_is_in_class);
      } else {
        if (from != 0) {
          macro_assembler->CheckCharacterLT(from, &next_range);
        }
        if (to != max_char) {
          macro_assembler->CheckCharacterLT(to + 1, char_is_in_class);
        } else {
          macro_assembler->GoTo(char_is_in_class);
        }
      }
      macro_assembler->Bind(&next_range);
    }
  
    CharacterRange& range = ranges->at(last_valid_range);
    uc16 from = range.from();
    uc16 to = range.to();
  
    if (to > max_char) to = max_char;
    ASSERT(to >= from);
  
    if (to == from) {
      if (cc->is_negated()) {
        macro_assembler->CheckCharacter(to, on_failure);
      } else {
        macro_assembler->CheckNotCharacter(to, on_failure);
      }
    } else {
      if (from != 0) {
        if (cc->is_negated()) {
          macro_assembler->CheckCharacterLT(from, &success);
        } else {
          macro_assembler->CheckCharacterLT(from, on_failure);
        }
      }
      if (to != String::kMaxUC16CharCode) {
        if (cc->is_negated()) {
          macro_assembler->CheckCharacterLT(to + 1, on_failure);
        } else {
          macro_assembler->CheckCharacterGT(to, on_failure);
        }
      } else {
        if (cc->is_negated()) {
          macro_assembler->GoTo(on_failure);
        }
      }
    }
    macro_assembler->Bind(&success);
  }
  
  
  RegExpNode::~RegExpNode() {
  }
  
  
  RegExpNode::LimitResult RegExpNode::LimitVersions(RegExpCompiler* compiler,
                                                    Trace* trace) {
    // If we are generating a greedy loop then don't stop and don't reuse code.
    if (trace->stop_node() != NULL) {
      return CONTINUE;
    }
  
    RegExpMacroAssembler* macro_assembler = compiler->macro_assembler();
    if (trace->is_trivial()) {
      if (label_.is_bound()) {
        // We are being asked to generate a generic version, but that's already
        // been done so just go to it.
        macro_assembler->GoTo(&label_);
        return DONE;
      }
      if (compiler->recursion_depth() >= RegExpCompiler::kMaxRecursion) {
        // To avoid too deep recursion we push the node to the work queue and just
        // generate a goto here.
        compiler->AddWork(this);
        macro_assembler->GoTo(&label_);
        return DONE;
      }
      // Generate generic version of the node and bind the label for later use.
      macro_assembler->Bind(&label_);
      return CONTINUE;
    }
  
    // We are being asked to make a non-generic version.  Keep track of how many
    // non-generic versions we generate so as not to overdo it.
    trace_count_++;
    if (FLAG_regexp_optimization &&
        trace_count_ < kMaxCopiesCodeGenerated &&
        compiler->recursion_depth() <= RegExpCompiler::kMaxRecursion) {
      return CONTINUE;
    }
  
    // If we get here code has been generated for this node too many times or
    // recursion is too deep.  Time to switch to a generic version.  The code for
    // generic versions above can handle deep recursion properly.
    trace->Flush(compiler, this);
    return DONE;
  }
  
  
  int ActionNode::EatsAtLeast(int still_to_find,
                              int recursion_depth,
                              bool not_at_start) {
    if (recursion_depth > RegExpCompiler::kMaxRecursion) return 0;
    if (type_ == POSITIVE_SUBMATCH_SUCCESS) return 0;  // Rewinds input!
    return on_success()->EatsAtLeast(still_to_find,
                                     recursion_depth + 1,
                                     not_at_start);
  }
  
  
  int AssertionNode::EatsAtLeast(int still_to_find,
                                 int recursion_depth,
                                 bool not_at_start) {
    if (recursion_depth > RegExpCompiler::kMaxRecursion) return 0;
    // If we know we are not at the start and we are asked "how many characters
    // will you match if you succeed?" then we can answer anything since false
    // implies false.  So lets just return the max answer (still_to_find) since
    // that won't prevent us from preloading a lot of characters for the other
    // branches in the node graph.
    if (type() == AT_START && not_at_start) return still_to_find;
    return on_success()->EatsAtLeast(still_to_find,
                                     recursion_depth + 1,
                                     not_at_start);
  }
  
  
  int BackReferenceNode::EatsAtLeast(int still_to_find,
                                     int recursion_depth,
                                     bool not_at_start) {
    if (recursion_depth > RegExpCompiler::kMaxRecursion) return 0;
    return on_success()->EatsAtLeast(still_to_find,
                                     recursion_depth + 1,
                                     not_at_start);
  }
  
  
  int TextNode::EatsAtLeast(int still_to_find,
                            int recursion_depth,
                            bool not_at_start) {
    int answer = Length();
    if (answer >= still_to_find) return answer;
    if (recursion_depth > RegExpCompiler::kMaxRecursion) return answer;
    // We are not at start after this node so we set the last argument to 'true'.
    return answer + on_success()->EatsAtLeast(still_to_find - answer,
                                              recursion_depth + 1,
                                              true);
  }
  
  
  int NegativeLookaheadChoiceNode::EatsAtLeast(int still_to_find,
                                               int recursion_depth,
                                               bool not_at_start) {
    if (recursion_depth > RegExpCompiler::kMaxRecursion) return 0;
    // Alternative 0 is the negative lookahead, alternative 1 is what comes
    // afterwards.
    RegExpNode* node = alternatives_->at(1).node();
    return node->EatsAtLeast(still_to_find, recursion_depth + 1, not_at_start);
  }
  
  
  void NegativeLookaheadChoiceNode::GetQuickCheckDetails(
      QuickCheckDetails* details,
      RegExpCompiler* compiler,
      int filled_in,
      bool not_at_start) {
    // Alternative 0 is the negative lookahead, alternative 1 is what comes
    // afterwards.
    RegExpNode* node = alternatives_->at(1).node();
    return node->GetQuickCheckDetails(details, compiler, filled_in, not_at_start);
  }
  
  
  int ChoiceNode::EatsAtLeastHelper(int still_to_find,
                                    int recursion_depth,
                                    RegExpNode* ignore_this_node,
                                    bool not_at_start) {
    if (recursion_depth > RegExpCompiler::kMaxRecursion) return 0;
    int min = 100;
    int choice_count = alternatives_->length();
    for (int i = 0; i < choice_count; i++) {
      RegExpNode* node = alternatives_->at(i).node();
      if (node == ignore_this_node) continue;
      int node_eats_at_least = node->EatsAtLeast(still_to_find,
                                                 recursion_depth + 1,
                                                 not_at_start);
      if (node_eats_at_least < min) min = node_eats_at_least;
    }
    return min;
  }
  
  
  int LoopChoiceNode::EatsAtLeast(int still_to_find,
                                  int recursion_depth,
                                  bool not_at_start) {
    return EatsAtLeastHelper(still_to_find,
                             recursion_depth,
                             loop_node_,
                             not_at_start);
  }
  
  
  int ChoiceNode::EatsAtLeast(int still_to_find,
                              int recursion_depth,
                              bool not_at_start) {
    return EatsAtLeastHelper(still_to_find,
                             recursion_depth,
                             NULL,
                             not_at_start);
  }
  
  
  // Takes the left-most 1-bit and smears it out, setting all bits to its right.
  static inline uint32_t SmearBitsRight(uint32_t v) {
    v |= v >> 1;
    v |= v >> 2;
    v |= v >> 4;
    v |= v >> 8;
    v |= v >> 16;
    return v;
  }
  
  
  bool QuickCheckDetails::Rationalize(bool asc) {
    bool found_useful_op = false;
    uint32_t char_mask;
    if (asc) {
      char_mask = String::kMaxAsciiCharCode;
    } else {
      char_mask = String::kMaxUC16CharCode;
    }
    mask_ = 0;
    value_ = 0;
    int char_shift = 0;
    for (int i = 0; i < characters_; i++) {
      Position* pos = &positions_[i];
      if ((pos->mask & String::kMaxAsciiCharCode) != 0) {
        found_useful_op = true;
      }
      mask_ |= (pos->mask & char_mask) << char_shift;
      value_ |= (pos->value & char_mask) << char_shift;
      char_shift += asc ? 8 : 16;
    }
    return found_useful_op;
  }
  
  
  bool RegExpNode::EmitQuickCheck(RegExpCompiler* compiler,
                                  Trace* trace,
                                  bool preload_has_checked_bounds,
                                  Label* on_possible_success,
                                  QuickCheckDetails* details,
                                  bool fall_through_on_failure) {
    if (details->characters() == 0) return false;
    GetQuickCheckDetails(details, compiler, 0, trace->at_start() == Trace::FALSE);
    if (details->cannot_match()) return false;
    if (!details->Rationalize(compiler->ascii())) return false;
    ASSERT(details->characters() == 1 ||
           compiler->macro_assembler()->CanReadUnaligned());
    uint32_t mask = details->mask();
    uint32_t value = details->value();
  
    RegExpMacroAssembler* assembler = compiler->macro_assembler();
  
    if (trace->characters_preloaded() != details->characters()) {
      assembler->LoadCurrentCharacter(trace->cp_offset(),
                                      trace->backtrack(),
                                      !preload_has_checked_bounds,
                                      details->characters());
    }
  
  
    bool need_mask = true;
  
    if (details->characters() == 1) {
      // If number of characters preloaded is 1 then we used a byte or 16 bit
      // load so the value is already masked down.
      uint32_t char_mask;
      if (compiler->ascii()) {
        char_mask = String::kMaxAsciiCharCode;
      } else {
        char_mask = String::kMaxUC16CharCode;
      }
      if ((mask & char_mask) == char_mask) need_mask = false;
      mask &= char_mask;
    } else {
      // For 2-character preloads in ASCII mode or 1-character preloads in
      // TWO_BYTE mode we also use a 16 bit load with zero extend.
      if (details->characters() == 2 && compiler->ascii()) {
        if ((mask & 0x7f7f) == 0x7f7f) need_mask = false;
      } else if (details->characters() == 1 && !compiler->ascii()) {
        if ((mask & 0xffff) == 0xffff) need_mask = false;
      } else {
        if (mask == 0xffffffff) need_mask = false;
      }
    }
  
    if (fall_through_on_failure) {
      if (need_mask) {
        assembler->CheckCharacterAfterAnd(value, mask, on_possible_success);
      } else {
        assembler->CheckCharacter(value, on_possible_success);
      }
    } else {
      if (need_mask) {
        assembler->CheckNotCharacterAfterAnd(value, mask, trace->backtrack());
      } else {
        assembler->CheckNotCharacter(value, trace->backtrack());
      }
    }
    return true;
  }
  
  
  // Here is the meat of GetQuickCheckDetails (see also the comment on the
  // super-class in the .h file).
  //
  // We iterate along the text object, building up for each character a
  // mask and value that can be used to test for a quick failure to match.
  // The masks and values for the positions will be combined into a single
  // machine word for the current character width in order to be used in
  // generating a quick check.
  void TextNode::GetQuickCheckDetails(QuickCheckDetails* details,
                                      RegExpCompiler* compiler,
                                      int characters_filled_in,
                                      bool not_at_start) {
    Isolate* isolate = Isolate::Current();
    ASSERT(characters_filled_in < details->characters());
    int characters = details->characters();
    int char_mask;
    if (compiler->ascii()) {
      char_mask = String::kMaxAsciiCharCode;
    } else {
      char_mask = String::kMaxUC16CharCode;
    }
    for (int k = 0; k < elms_->length(); k++) {
      TextElement elm = elms_->at(k);
      if (elm.type == TextElement::ATOM) {
        Vector<const uc16> quarks = elm.data.u_atom->data();
        for (int i = 0; i < characters && i < quarks.length(); i++) {
          QuickCheckDetails::Position* pos =
              details->positions(characters_filled_in);
          uc16 c = quarks[i];
          if (c > char_mask) {
            // If we expect a non-ASCII character from an ASCII string,
            // there is no way we can match. Not even case independent
            // matching can turn an ASCII character into non-ASCII or
            // vice versa.
            details->set_cannot_match();
            pos->determines_perfectly = false;
            return;
          }
          if (compiler->ignore_case()) {
            unibrow::uchar chars[unibrow::Ecma262UnCanonicalize::kMaxWidth];
            int length = GetCaseIndependentLetters(isolate, c, compiler->ascii(),
                                                   chars);
            ASSERT(length != 0);  // Can only happen if c > char_mask (see above).
            if (length == 1) {
              // This letter has no case equivalents, so it's nice and simple
              // and the mask-compare will determine definitely whether we have
              // a match at this character position.
              pos->mask = char_mask;
              pos->value = c;
              pos->determines_perfectly = true;
            } else {
              uint32_t common_bits = char_mask;
              uint32_t bits = chars[0];
              for (int j = 1; j < length; j++) {
                uint32_t differing_bits = ((chars[j] & common_bits) ^ bits);
                common_bits ^= differing_bits;
                bits &= common_bits;
              }
              // If length is 2 and common bits has only one zero in it then
              // our mask and compare instruction will determine definitely
              // whether we have a match at this character position.  Otherwise
              // it can only be an approximate check.
              uint32_t one_zero = (common_bits | ~char_mask);
              if (length == 2 && ((~one_zero) & ((~one_zero) - 1)) == 0) {
                pos->determines_perfectly = true;
              }
              pos->mask = common_bits;
              pos->value = bits;
            }
          } else {
            // Don't ignore case.  Nice simple case where the mask-compare will
            // determine definitely whether we have a match at this character
            // position.
            pos->mask = char_mask;
            pos->value = c;
            pos->determines_perfectly = true;
          }
          characters_filled_in++;
          ASSERT(characters_filled_in <= details->characters());
          if (characters_filled_in == details->characters()) {
            return;
          }
        }
      } else {
        QuickCheckDetails::Position* pos =
            details->positions(characters_filled_in);
        RegExpCharacterClass* tree = elm.data.u_char_class;
        ZoneList<CharacterRange>* ranges = tree->ranges();
        if (tree->is_negated()) {
          // A quick check uses multi-character mask and compare.  There is no
          // useful way to incorporate a negative char class into this scheme
          // so we just conservatively create a mask and value that will always
          // succeed.
          pos->mask = 0;
          pos->value = 0;
        } else {
          int first_range = 0;
          while (ranges->at(first_range).from() > char_mask) {
            first_range++;
            if (first_range == ranges->length()) {
              details->set_cannot_match();
              pos->determines_perfectly = false;
              return;
            }
          }
          CharacterRange range = ranges->at(first_range);
          uc16 from = range.from();
          uc16 to = range.to();
          if (to > char_mask) {
            to = char_mask;
          }
          uint32_t differing_bits = (from ^ to);
          // A mask and compare is only perfect if the differing bits form a
          // number like 00011111 with one single block of trailing 1s.
          if ((differing_bits & (differing_bits + 1)) == 0 &&
               from + differing_bits == to) {
            pos->determines_perfectly = true;
          }
          uint32_t common_bits = ~SmearBitsRight(differing_bits);
          uint32_t bits = (from & common_bits);
          for (int i = first_range + 1; i < ranges->length(); i++) {
            CharacterRange range = ranges->at(i);
            uc16 from = range.from();
            uc16 to = range.to();
            if (from > char_mask) continue;
            if (to > char_mask) to = char_mask;
            // Here we are combining more ranges into the mask and compare
            // value.  With each new range the mask becomes more sparse and
            // so the chances of a false positive rise.  A character class
            // with multiple ranges is assumed never to be equivalent to a
            // mask and compare operation.
            pos->determines_perfectly = false;
            uint32_t new_common_bits = (from ^ to);
            new_common_bits = ~SmearBitsRight(new_common_bits);
            common_bits &= new_common_bits;
            bits &= new_common_bits;
            uint32_t differing_bits = (from & common_bits) ^ bits;
            common_bits ^= differing_bits;
            bits &= common_bits;
          }
          pos->mask = common_bits;
          pos->value = bits;
        }
        characters_filled_in++;
        ASSERT(characters_filled_in <= details->characters());
        if (characters_filled_in == details->characters()) {
          return;
        }
      }
    }
    ASSERT(characters_filled_in != details->characters());
    on_success()-> GetQuickCheckDetails(details,
                                        compiler,
                                        characters_filled_in,
                                        true);
  }
  
  
  void QuickCheckDetails::Clear() {
    for (int i = 0; i < characters_; i++) {
      positions_[i].mask = 0;
      positions_[i].value = 0;
      positions_[i].determines_perfectly = false;
    }
    characters_ = 0;
  }
  
  
  void QuickCheckDetails::Advance(int by, bool ascii) {
    ASSERT(by >= 0);
    if (by >= characters_) {
      Clear();
      return;
    }
    for (int i = 0; i < characters_ - by; i++) {
      positions_[i] = positions_[by + i];
    }
    for (int i = characters_ - by; i < characters_; i++) {
      positions_[i].mask = 0;
      positions_[i].value = 0;
      positions_[i].determines_perfectly = false;
    }
    characters_ -= by;
    // We could change mask_ and value_ here but we would never advance unless
    // they had already been used in a check and they won't be used again because
    // it would gain us nothing.  So there's no point.
  }
  
  
  void QuickCheckDetails::Merge(QuickCheckDetails* other, int from_index) {
    ASSERT(characters_ == other->characters_);
    if (other->cannot_match_) {
      return;
    }
    if (cannot_match_) {
      *this = *other;
      return;
    }
    for (int i = from_index; i < characters_; i++) {
      QuickCheckDetails::Position* pos = positions(i);
      QuickCheckDetails::Position* other_pos = other->positions(i);
      if (pos->mask != other_pos->mask ||
          pos->value != other_pos->value ||
          !other_pos->determines_perfectly) {
        // Our mask-compare operation will be approximate unless we have the
        // exact same operation on both sides of the alternation.
        pos->determines_perfectly = false;
      }
      pos->mask &= other_pos->mask;
      pos->value &= pos->mask;
      other_pos->value &= pos->mask;
      uc16 differing_bits = (pos->value ^ other_pos->value);
      pos->mask &= ~differing_bits;
      pos->value &= pos->mask;
    }
  }
  
  
  class VisitMarker {
   public:
    explicit VisitMarker(NodeInfo* info) : info_(info) {
      ASSERT(!info->visited);
      info->visited = true;
    }
    ~VisitMarker() {
      info_->visited = false;
    }
   private:
    NodeInfo* info_;
  };
  
  
  void LoopChoiceNode::GetQuickCheckDetails(QuickCheckDetails* details,
                                            RegExpCompiler* compiler,
                                            int characters_filled_in,
                                            bool not_at_start) {
    if (body_can_be_zero_length_ || info()->visited) return;
    VisitMarker marker(info());
    return ChoiceNode::GetQuickCheckDetails(details,
                                            compiler,
                                            characters_filled_in,
                                            not_at_start);
  }
  
  
  void ChoiceNode::GetQuickCheckDetails(QuickCheckDetails* details,
                                        RegExpCompiler* compiler,
                                        int characters_filled_in,
                                        bool not_at_start) {
    not_at_start = (not_at_start || not_at_start_);
    int choice_count = alternatives_->length();
    ASSERT(choice_count > 0);
    alternatives_->at(0).node()->GetQuickCheckDetails(details,
                                                      compiler,
                                                      characters_filled_in,
                                                      not_at_start);
    for (int i = 1; i < choice_count; i++) {
      QuickCheckDetails new_details(details->characters());
      RegExpNode* node = alternatives_->at(i).node();
      node->GetQuickCheckDetails(&new_details, compiler,
                                 characters_filled_in,
                                 not_at_start);
      // Here we merge the quick match details of the two branches.
      details->Merge(&new_details, characters_filled_in);
    }
  }
  
  
  // Check for [0-9A-Z_a-z].
  static void EmitWordCheck(RegExpMacroAssembler* assembler,
                            Label* word,
                            Label* non_word,
                            bool fall_through_on_word) {
    if (assembler->CheckSpecialCharacterClass(
            fall_through_on_word ? 'w' : 'W',
            fall_through_on_word ? non_word : word)) {
      // Optimized implementation available.
      return;
    }
    assembler->CheckCharacterGT('z', non_word);
    assembler->CheckCharacterLT('0', non_word);
    assembler->CheckCharacterGT('a' - 1, word);
    assembler->CheckCharacterLT('9' + 1, word);
    assembler->CheckCharacterLT('A', non_word);
    assembler->CheckCharacterLT('Z' + 1, word);
    if (fall_through_on_word) {
      assembler->CheckNotCharacter('_', non_word);
    } else {
      assembler->CheckCharacter('_', word);
    }
  }
  
  
  // Emit the code to check for a ^ in multiline mode (1-character lookbehind
  // that matches newline or the start of input).
  static void EmitHat(RegExpCompiler* compiler,
                      RegExpNode* on_success,
                      Trace* trace) {
    RegExpMacroAssembler* assembler = compiler->macro_assembler();
    // We will be loading the previous character into the current character
    // register.
    Trace new_trace(*trace);
    new_trace.InvalidateCurrentCharacter();
  
    Label ok;
    if (new_trace.cp_offset() == 0) {
      // The start of input counts as a newline in this context, so skip to
      // ok if we are at the start.
      assembler->CheckAtStart(&ok);
    }
    // We already checked that we are not at the start of input so it must be
    // OK to load the previous character.
    assembler->LoadCurrentCharacter(new_trace.cp_offset() -1,
                                    new_trace.backtrack(),
                                    false);
    if (!assembler->CheckSpecialCharacterClass('n',
                                               new_trace.backtrack())) {
      // Newline means \n, \r, 0x2028 or 0x2029.
      if (!compiler->ascii()) {
        assembler->CheckCharacterAfterAnd(0x2028, 0xfffe, &ok);
      }
      assembler->CheckCharacter('\n', &ok);
      assembler->CheckNotCharacter('\r', new_trace.backtrack());
    }
    assembler->Bind(&ok);
    on_success->Emit(compiler, &new_trace);
  }
  
  
  // Emit the code to handle \b and \B (word-boundary or non-word-boundary)
  // when we know whether the next character must be a word character or not.
  static void EmitHalfBoundaryCheck(AssertionNode::AssertionNodeType type,
                                    RegExpCompiler* compiler,
                                    RegExpNode* on_success,
                                    Trace* trace) {
    RegExpMacroAssembler* assembler = compiler->macro_assembler();
    Label done;
  
    Trace new_trace(*trace);
  
    bool expect_word_character = (type == AssertionNode::AFTER_WORD_CHARACTER);
    Label* on_word = expect_word_character ? &done : new_trace.backtrack();
    Label* on_non_word = expect_word_character ? new_trace.backtrack() : &done;
  
    // Check whether previous character was a word character.
    switch (trace->at_start()) {
      case Trace::TRUE:
        if (expect_word_character) {
          assembler->GoTo(on_non_word);
        }
        break;
      case Trace::UNKNOWN:
        ASSERT_EQ(0, trace->cp_offset());
        assembler->CheckAtStart(on_non_word);
        // Fall through.
      case Trace::FALSE:
        int prev_char_offset = trace->cp_offset() - 1;
        assembler->LoadCurrentCharacter(prev_char_offset, NULL, false, 1);
        EmitWordCheck(assembler, on_word, on_non_word, expect_word_character);
        // We may or may not have loaded the previous character.
        new_trace.InvalidateCurrentCharacter();
    }
  
    assembler->Bind(&done);
  
    on_success->Emit(compiler, &new_trace);
  }
  
  
  // Emit the code to handle \b and \B (word-boundary or non-word-boundary).
  static void EmitBoundaryCheck(AssertionNode::AssertionNodeType type,
                                RegExpCompiler* compiler,
                                RegExpNode* on_success,
                                Trace* trace) {
    RegExpMacroAssembler* assembler = compiler->macro_assembler();
    Label before_non_word;
    Label before_word;
    if (trace->characters_preloaded() != 1) {
      assembler->LoadCurrentCharacter(trace->cp_offset(), &before_non_word);
    }
    // Fall through on non-word.
    EmitWordCheck(assembler, &before_word, &before_non_word, false);
  
    // We will be loading the previous character into the current character
    // register.
    Trace new_trace(*trace);
    new_trace.InvalidateCurrentCharacter();
  
    Label ok;
    Label* boundary;
    Label* not_boundary;
    if (type == AssertionNode::AT_BOUNDARY) {
      boundary = &ok;
      not_boundary = new_trace.backtrack();
    } else {
      not_boundary = &ok;
      boundary = new_trace.backtrack();
    }
  
    // Next character is not a word character.
    assembler->Bind(&before_non_word);
    if (new_trace.cp_offset() == 0) {
      // The start of input counts as a non-word character, so the question is
      // decided if we are at the start.
      assembler->CheckAtStart(not_boundary);
    }
    // We already checked that we are not at the start of input so it must be
    // OK to load the previous character.
    assembler->LoadCurrentCharacter(new_trace.cp_offset() - 1,
                                    &ok,  // Unused dummy label in this call.
                                    false);
    // Fall through on non-word.
    EmitWordCheck(assembler, boundary, not_boundary, false);
    assembler->GoTo(not_boundary);
  
    // Next character is a word character.
    assembler->Bind(&before_word);
    if (new_trace.cp_offset() == 0) {
      // The start of input counts as a non-word character, so the question is
      // decided if we are at the start.
      assembler->CheckAtStart(boundary);
    }
    // We already checked that we are not at the start of input so it must be
    // OK to load the previous character.
    assembler->LoadCurrentCharacter(new_trace.cp_offset() - 1,
                                    &ok,  // Unused dummy label in this call.
                                    false);
    bool fall_through_on_word = (type == AssertionNode::AT_NON_BOUNDARY);
    EmitWordCheck(assembler, not_boundary, boundary, fall_through_on_word);
  
    assembler->Bind(&ok);
  
    on_success->Emit(compiler, &new_trace);
  }
  
  
  void AssertionNode::GetQuickCheckDetails(QuickCheckDetails* details,
                                           RegExpCompiler* compiler,
                                           int filled_in,
                                           bool not_at_start) {
    if (type_ == AT_START && not_at_start) {
      details->set_cannot_match();
      return;
    }
    return on_success()->GetQuickCheckDetails(details,
                                              compiler,
                                              filled_in,
                                              not_at_start);
  }
  
  
  void AssertionNode::Emit(RegExpCompiler* compiler, Trace* trace) {
    RegExpMacroAssembler* assembler = compiler->macro_assembler();
    switch (type_) {
      case AT_END: {
        Label ok;
        assembler->CheckPosition(trace->cp_offset(), &ok);
        assembler->GoTo(trace->backtrack());
        assembler->Bind(&ok);
        break;
      }
      case AT_START: {
        if (trace->at_start() == Trace::FALSE) {
          assembler->GoTo(trace->backtrack());
          return;
        }
        if (trace->at_start() == Trace::UNKNOWN) {
          assembler->CheckNotAtStart(trace->backtrack());
          Trace at_start_trace = *trace;
          at_start_trace.set_at_start(true);
          on_success()->Emit(compiler, &at_start_trace);
          return;
        }
      }
      break;
      case AFTER_NEWLINE:
        EmitHat(compiler, on_success(), trace);
        return;
      case AT_BOUNDARY:
      case AT_NON_BOUNDARY: {
        EmitBoundaryCheck(type_, compiler, on_success(), trace);
        return;
      }
      case AFTER_WORD_CHARACTER:
      case AFTER_NONWORD_CHARACTER: {
        EmitHalfBoundaryCheck(type_, compiler, on_success(), trace);
      }
    }
    on_success()->Emit(compiler, trace);
  }
  
  
  static bool DeterminedAlready(QuickCheckDetails* quick_check, int offset) {
    if (quick_check == NULL) return false;
    if (offset >= quick_check->characters()) return false;
    return quick_check->positions(offset)->determines_perfectly;
  }
  
  
  static void UpdateBoundsCheck(int index, int* checked_up_to) {
    if (index > *checked_up_to) {
      *checked_up_to = index;
    }
  }
  
  
  // We call this repeatedly to generate code for each pass over the text node.
  // The passes are in increasing order of difficulty because we hope one
  // of the first passes will fail in which case we are saved the work of the
  // later passes.  for example for the case independent regexp /%[asdfghjkl]a/
  // we will check the '%' in the first pass, the case independent 'a' in the
  // second pass and the character class in the last pass.
  //
  // The passes are done from right to left, so for example to test for /bar/
  // we will first test for an 'r' with offset 2, then an 'a' with offset 1
  // and then a 'b' with offset 0.  This means we can avoid the end-of-input
  // bounds check most of the time.  In the example we only need to check for
  // end-of-input when loading the putative 'r'.
  //
  // A slight complication involves the fact that the first character may already
  // be fetched into a register by the previous node.  In this case we want to
  // do the test for that character first.  We do this in separate passes.  The
  // 'preloaded' argument indicates that we are doing such a 'pass'.  If such a
  // pass has been performed then subsequent passes will have true in
  // first_element_checked to indicate that that character does not need to be
  // checked again.
  //
  // In addition to all this we are passed a Trace, which can
  // contain an AlternativeGeneration object.  In this AlternativeGeneration
  // object we can see details of any quick check that was already passed in
  // order to get to the code we are now generating.  The quick check can involve
  // loading characters, which means we do not need to recheck the bounds
  // up to the limit the quick check already checked.  In addition the quick
  // check can have involved a mask and compare operation which may simplify
  // or obviate the need for further checks at some character positions.
  void TextNode::TextEmitPass(RegExpCompiler* compiler,
                              TextEmitPassType pass,
                              bool preloaded,
                              Trace* trace,
                              bool first_element_checked,
                              int* checked_up_to) {
    Isolate* isolate = Isolate::Current();
    RegExpMacroAssembler* assembler = compiler->macro_assembler();
    bool ascii = compiler->ascii();
    Label* backtrack = trace->backtrack();
    QuickCheckDetails* quick_check = trace->quick_check_performed();
    int element_count = elms_->length();
    for (int i = preloaded ? 0 : element_count - 1; i >= 0; i--) {
      TextElement elm = elms_->at(i);
      int cp_offset = trace->cp_offset() + elm.cp_offset;
      if (elm.type == TextElement::ATOM) {
        Vector<const uc16> quarks = elm.data.u_atom->data();
        for (int j = preloaded ? 0 : quarks.length() - 1; j >= 0; j--) {
          if (first_element_checked && i == 0 && j == 0) continue;
          if (DeterminedAlready(quick_check, elm.cp_offset + j)) continue;
          EmitCharacterFunction* emit_function = NULL;
          switch (pass) {
            case NON_ASCII_MATCH:
              ASSERT(ascii);
              if (quarks[j] > String::kMaxAsciiCharCode) {
                assembler->GoTo(backtrack);
                return;
              }
              break;
            case NON_LETTER_CHARACTER_MATCH:
              emit_function = &EmitAtomNonLetter;
              break;
            case SIMPLE_CHARACTER_MATCH:
              emit_function = &EmitSimpleCharacter;
              break;
            case CASE_CHARACTER_MATCH:
              emit_function = &EmitAtomLetter;
              break;
            default:
              break;
          }
          if (emit_function != NULL) {
            bool bound_checked = emit_function(isolate,
                                               compiler,
                                               quarks[j],
                                               backtrack,
                                               cp_offset + j,
                                               *checked_up_to < cp_offset + j,
                                               preloaded);
            if (bound_checked) UpdateBoundsCheck(cp_offset + j, checked_up_to);
          }
        }
      } else {
        ASSERT_EQ(elm.type, TextElement::CHAR_CLASS);
        if (pass == CHARACTER_CLASS_MATCH) {
          if (first_element_checked && i == 0) continue;
          if (DeterminedAlready(quick_check, elm.cp_offset)) continue;
          RegExpCharacterClass* cc = elm.data.u_char_class;
          EmitCharClass(assembler,
                        cc,
                        ascii,
                        backtrack,
                        cp_offset,
                        *checked_up_to < cp_offset,
                        preloaded);
          UpdateBoundsCheck(cp_offset, checked_up_to);
        }
      }
    }
  }
  
  
  int TextNode::Length() {
    TextElement elm = elms_->last();
    ASSERT(elm.cp_offset >= 0);
    if (elm.type == TextElement::ATOM) {
      return elm.cp_offset + elm.data.u_atom->data().length();
    } else {
      return elm.cp_offset + 1;
    }
  }
  
  
  bool TextNode::SkipPass(int int_pass, bool ignore_case) {
    TextEmitPassType pass = static_cast<TextEmitPassType>(int_pass);
    if (ignore_case) {
      return pass == SIMPLE_CHARACTER_MATCH;
    } else {
      return pass == NON_LETTER_CHARACTER_MATCH || pass == CASE_CHARACTER_MATCH;
    }
  }
  
  
  // This generates the code to match a text node.  A text node can contain
  // straight character sequences (possibly to be matched in a case-independent
  // way) and character classes.  For efficiency we do not do this in a single
  // pass from left to right.  Instead we pass over the text node several times,
  // emitting code for some character positions every time.  See the comment on
  // TextEmitPass for details.
  void TextNode::Emit(RegExpCompiler* compiler, Trace* trace) {
    LimitResult limit_result = LimitVersions(compiler, trace);
    if (limit_result == DONE) return;
    ASSERT(limit_result == CONTINUE);
  
    if (trace->cp_offset() + Length() > RegExpMacroAssembler::kMaxCPOffset) {
      compiler->SetRegExpTooBig();
      return;
    }
  
    if (compiler->ascii()) {
      int dummy = 0;
      TextEmitPass(compiler, NON_ASCII_MATCH, false, trace, false, &dummy);
    }
  
    bool first_elt_done = false;
    int bound_checked_to = trace->cp_offset() - 1;
    bound_checked_to += trace->bound_checked_up_to();
  
    // If a character is preloaded into the current character register then
    // check that now.
    if (trace->characters_preloaded() == 1) {
      for (int pass = kFirstRealPass; pass <= kLastPass; pass++) {
        if (!SkipPass(pass, compiler->ignore_case())) {
          TextEmitPass(compiler,
                       static_cast<TextEmitPassType>(pass),
                       true,
                       trace,
                       false,
                       &bound_checked_to);
        }
      }
      first_elt_done = true;
    }
  
    for (int pass = kFirstRealPass; pass <= kLastPass; pass++) {
      if (!SkipPass(pass, compiler->ignore_case())) {
        TextEmitPass(compiler,
                     static_cast<TextEmitPassType>(pass),
                     false,
                     trace,
                     first_elt_done,
                     &bound_checked_to);
      }
    }
  
    Trace successor_trace(*trace);
    successor_trace.set_at_start(false);
    successor_trace.AdvanceCurrentPositionInTrace(Length(), compiler);
    RecursionCheck rc(compiler);
    on_success()->Emit(compiler, &successor_trace);
  }
  
  
  void Trace::InvalidateCurrentCharacter() {
    characters_preloaded_ = 0;
  }
  
  
  void Trace::AdvanceCurrentPositionInTrace(int by, RegExpCompiler* compiler) {
    ASSERT(by > 0);
    // We don't have an instruction for shifting the current character register
    // down or for using a shifted value for anything so lets just forget that
    // we preloaded any characters into it.
    characters_preloaded_ = 0;
    // Adjust the offsets of the quick check performed information.  This
    // information is used to find out what we already determined about the
    // characters by means of mask and compare.
    quick_check_performed_.Advance(by, compiler->ascii());
    cp_offset_ += by;
    if (cp_offset_ > RegExpMacroAssembler::kMaxCPOffset) {
      compiler->SetRegExpTooBig();
      cp_offset_ = 0;
    }
    bound_checked_up_to_ = Max(0, bound_checked_up_to_ - by);
  }
  
  
  void TextNode::MakeCaseIndependent(bool is_ascii) {
    int element_count = elms_->length();
    for (int i = 0; i < element_count; i++) {
      TextElement elm = elms_->at(i);
      if (elm.type == TextElement::CHAR_CLASS) {
        RegExpCharacterClass* cc = elm.data.u_char_class;
        // None of the standard character classes is different in the case
        // independent case and it slows us down if we don't know that.
        if (cc->is_standard()) continue;
        ZoneList<CharacterRange>* ranges = cc->ranges();
        int range_count = ranges->length();
        for (int j = 0; j < range_count; j++) {
          ranges->at(j).AddCaseEquivalents(ranges, is_ascii);
        }
      }
    }
  }
  
  
  int TextNode::GreedyLoopTextLength() {
    TextElement elm = elms_->at(elms_->length() - 1);
    if (elm.type == TextElement::CHAR_CLASS) {
      return elm.cp_offset + 1;
    } else {
      return elm.cp_offset + elm.data.u_atom->data().length();
    }
  }
  
  
  // Finds the fixed match length of a sequence of nodes that goes from
  // this alternative and back to this choice node.  If there are variable
  // length nodes or other complications in the way then return a sentinel
  // value indicating that a greedy loop cannot be constructed.
  int ChoiceNode::GreedyLoopTextLengthForAlternative(
      GuardedAlternative* alternative) {
    int length = 0;
    RegExpNode* node = alternative->node();
    // Later we will generate code for all these text nodes using recursion
    // so we have to limit the max number.
    int recursion_depth = 0;
    while (node != this) {
      if (recursion_depth++ > RegExpCompiler::kMaxRecursion) {
        return kNodeIsTooComplexForGreedyLoops;
      }
      int node_length = node->GreedyLoopTextLength();
      if (node_length == kNodeIsTooComplexForGreedyLoops) {
        return kNodeIsTooComplexForGreedyLoops;
      }
      length += node_length;
      SeqRegExpNode* seq_node = static_cast<SeqRegExpNode*>(node);
      node = seq_node->on_success();
    }
    return length;
  }
  
  
  void LoopChoiceNode::AddLoopAlternative(GuardedAlternative alt) {
    ASSERT_EQ(loop_node_, NULL);
    AddAlternative(alt);
    loop_node_ = alt.node();
  }
  
  
  void LoopChoiceNode::AddContinueAlternative(GuardedAlternative alt) {
    ASSERT_EQ(continue_node_, NULL);
    AddAlternative(alt);
    continue_node_ = alt.node();
  }
  
  
  void LoopChoiceNode::Emit(RegExpCompiler* compiler, Trace* trace) {
    RegExpMacroAssembler* macro_assembler = compiler->macro_assembler();
    if (trace->stop_node() == this) {
      int text_length =
          GreedyLoopTextLengthForAlternative(&(alternatives_->at(0)));
      ASSERT(text_length != kNodeIsTooComplexForGreedyLoops);
      // Update the counter-based backtracking info on the stack.  This is an
      // optimization for greedy loops (see below).
      ASSERT(trace->cp_offset() == text_length);
      macro_assembler->AdvanceCurrentPosition(text_length);
      macro_assembler->GoTo(trace->loop_label());
      return;
    }
    ASSERT(trace->stop_node() == NULL);
    if (!trace->is_trivial()) {
      trace->Flush(compiler, this);
      return;
    }
    ChoiceNode::Emit(compiler, trace);
  }
  
  
  int ChoiceNode::CalculatePreloadCharacters(RegExpCompiler* compiler,
                                             bool not_at_start) {
    int preload_characters = EatsAtLeast(4, 0, not_at_start);
    if (compiler->macro_assembler()->CanReadUnaligned()) {
      bool ascii = compiler->ascii();
      if (ascii) {
        if (preload_characters > 4) preload_characters = 4;
        // We can't preload 3 characters because there is no machine instruction
        // to do that.  We can't just load 4 because we could be reading
        // beyond the end of the string, which could cause a memory fault.
        if (preload_characters == 3) preload_characters = 2;
      } else {
        if (preload_characters > 2) preload_characters = 2;
      }
    } else {
      if (preload_characters > 1) preload_characters = 1;
    }
    return preload_characters;
  }
  
  
  // This class is used when generating the alternatives in a choice node.  It
  // records the way the alternative is being code generated.
  class AlternativeGeneration: public Malloced {
   public:
    AlternativeGeneration()
        : possible_success(),
          expects_preload(false),
          after(),
          quick_check_details() { }
    Label possible_success;
    bool expects_preload;
    Label after;
    QuickCheckDetails quick_check_details;
  };
  
  
  // Creates a list of AlternativeGenerations.  If the list has a reasonable
  // size then it is on the stack, otherwise the excess is on the heap.
  class AlternativeGenerationList {
   public:
    explicit AlternativeGenerationList(int count)
        : alt_gens_(count) {
      for (int i = 0; i < count && i < kAFew; i++) {
        alt_gens_.Add(a_few_alt_gens_ + i);
      }
      for (int i = kAFew; i < count; i++) {
        alt_gens_.Add(new AlternativeGeneration());
      }
    }
    ~AlternativeGenerationList() {
      for (int i = kAFew; i < alt_gens_.length(); i++) {
        delete alt_gens_[i];
        alt_gens_[i] = NULL;
      }
    }
  
    AlternativeGeneration* at(int i) {
      return alt_gens_[i];
    }
  
   private:
    static const int kAFew = 10;
    ZoneList<AlternativeGeneration*> alt_gens_;
    AlternativeGeneration a_few_alt_gens_[kAFew];
  };
  
  
  /* Code generation for choice nodes.
   *
   * We generate quick checks that do a mask and compare to eliminate a
   * choice.  If the quick check succeeds then it jumps to the continuation to
   * do slow checks and check subsequent nodes.  If it fails (the common case)
   * it falls through to the next choice.
   *
   * Here is the desired flow graph.  Nodes directly below each other imply
   * fallthrough.  Alternatives 1 and 2 have quick checks.  Alternative
   * 3 doesn't have a quick check so we have to call the slow check.
   * Nodes are marked Qn for quick checks and Sn for slow checks.  The entire
   * regexp continuation is generated directly after the Sn node, up to the
   * next GoTo if we decide to reuse some already generated code.  Some
   * nodes expect preload_characters to be preloaded into the current
   * character register.  R nodes do this preloading.  Vertices are marked
   * F for failures and S for success (possible success in the case of quick
   * nodes).  L, V, < and > are used as arrow heads.
   *
   * ----------> R
   *             |
   *             V
   *            Q1 -----> S1
   *             |   S   /
   *            F|      /
   *             |    F/
   *             |    /
   *             |   R
   *             |  /
   *             V L
   *            Q2 -----> S2
   *             |   S   /
   *            F|      /
   *             |    F/
   *             |    /
   *             |   R
   *             |  /
   *             V L
   *            S3
   *             |
   *            F|
   *             |
   *             R
   *             |
   * backtrack   V
   * <----------Q4
   *   \    F    |
   *    \        |S
   *     \   F   V
   *      \-----S4
   *
   * For greedy loops we reverse our expectation and expect to match rather
   * than fail. Therefore we want the loop code to look like this (U is the
   * unwind code that steps back in the greedy loop).  The following alternatives
   * look the same as above.
   *              _____
   *             /     \
   *             V     |
   * ----------> S1    |
   *            /|     |
   *           / |S    |
   *         F/  \_____/
   *         /
   *        |<-----------
   *        |            \
   *        V             \
   *        Q2 ---> S2     \
   *        |  S   /       |
   *       F|     /        |
   *        |   F/         |
   *        |   /          |
   *        |  R           |
   *        | /            |
   *   F    VL             |
   * <------U              |
   * back   |S             |
   *        \______________/
   */
  
  
  void ChoiceNode::Emit(RegExpCompiler* compiler, Trace* trace) {
    RegExpMacroAssembler* macro_assembler = compiler->macro_assembler();
    int choice_count = alternatives_->length();
  #ifdef DEBUG
    for (int i = 0; i < choice_count - 1; i++) {
      GuardedAlternative alternative = alternatives_->at(i);
      ZoneList<Guard*>* guards = alternative.guards();
      int guard_count = (guards == NULL) ? 0 : guards->length();
      for (int j = 0; j < guard_count; j++) {
        ASSERT(!trace->mentions_reg(guards->at(j)->reg()));
      }
    }
  #endif
  
    LimitResult limit_result = LimitVersions(compiler, trace);
    if (limit_result == DONE) return;
    ASSERT(limit_result == CONTINUE);
  
    int new_flush_budget = trace->flush_budget() / choice_count;
    if (trace->flush_budget() == 0 && trace->actions() != NULL) {
      trace->Flush(compiler, this);
      return;
    }
  
    RecursionCheck rc(compiler);
  
    Trace* current_trace = trace;
  
    int text_length = GreedyLoopTextLengthForAlternative(&(alternatives_->at(0)));
    bool greedy_loop = false;
    Label greedy_loop_label;
    Trace counter_backtrack_trace;
    counter_backtrack_trace.set_backtrack(&greedy_loop_label);
    if (not_at_start()) counter_backtrack_trace.set_at_start(false);
  
    if (choice_count > 1 && text_length != kNodeIsTooComplexForGreedyLoops) {
      // Here we have special handling for greedy loops containing only text nodes
      // and other simple nodes.  These are handled by pushing the current
      // position on the stack and then incrementing the current position each
      // time around the switch.  On backtrack we decrement the current position
      // and check it against the pushed value.  This avoids pushing backtrack
      // information for each iteration of the loop, which could take up a lot of
      // space.
      greedy_loop = true;
      ASSERT(trace->stop_node() == NULL);
      macro_assembler->PushCurrentPosition();
      current_trace = &counter_backtrack_trace;
      Label greedy_match_failed;
      Trace greedy_match_trace;
      if (not_at_start()) greedy_match_trace.set_at_start(false);
      greedy_match_trace.set_backtrack(&greedy_match_failed);
      Label loop_label;
      macro_assembler->Bind(&loop_label);
      greedy_match_trace.set_stop_node(this);
      greedy_match_trace.set_loop_label(&loop_label);
      alternatives_->at(0).node()->Emit(compiler, &greedy_match_trace);
      macro_assembler->Bind(&greedy_match_failed);
    }
  
    Label second_choice;  // For use in greedy matches.
    macro_assembler->Bind(&second_choice);
  
    int first_normal_choice = greedy_loop ? 1 : 0;
  
    int preload_characters =
        CalculatePreloadCharacters(compiler,
                                   current_trace->at_start() == Trace::FALSE);
    bool preload_is_current =
        (current_trace->characters_preloaded() == preload_characters);
    bool preload_has_checked_bounds = preload_is_current;
  
    AlternativeGenerationList alt_gens(choice_count);
  
    // For now we just call all choices one after the other.  The idea ultimately
    // is to use the Dispatch table to try only the relevant ones.
    for (int i = first_normal_choice; i < choice_count; i++) {
      GuardedAlternative alternative = alternatives_->at(i);
      AlternativeGeneration* alt_gen = alt_gens.at(i);
      alt_gen->quick_check_details.set_characters(preload_characters);
      ZoneList<Guard*>* guards = alternative.guards();
      int guard_count = (guards == NULL) ? 0 : guards->length();
      Trace new_trace(*current_trace);
      new_trace.set_characters_preloaded(preload_is_current ?
                                           preload_characters :
                                           0);
      if (preload_has_checked_bounds) {
        new_trace.set_bound_checked_up_to(preload_characters);
      }
      new_trace.quick_check_performed()->Clear();
      if (not_at_start_) new_trace.set_at_start(Trace::FALSE);
      alt_gen->expects_preload = preload_is_current;
      bool generate_full_check_inline = false;
      if (FLAG_regexp_optimization &&
          try_to_emit_quick_check_for_alternative(i) &&
          alternative.node()->EmitQuickCheck(compiler,
                                             &new_trace,
                                             preload_has_checked_bounds,
                                             &alt_gen->possible_success,
                                             &alt_gen->quick_check_details,
                                             i < choice_count - 1)) {
        // Quick check was generated for this choice.
        preload_is_current = true;
        preload_has_checked_bounds = true;
        // On the last choice in the ChoiceNode we generated the quick
        // check to fall through on possible success.  So now we need to
        // generate the full check inline.
        if (i == choice_count - 1) {
          macro_assembler->Bind(&alt_gen->possible_success);
          new_trace.set_quick_check_performed(&alt_gen->quick_check_details);
          new_trace.set_characters_preloaded(preload_characters);
          new_trace.set_bound_checked_up_to(preload_characters);
          generate_full_check_inline = true;
        }
      } else if (alt_gen->quick_check_details.cannot_match()) {
        if (i == choice_count - 1 && !greedy_loop) {
          macro_assembler->GoTo(trace->backtrack());
        }
        continue;
      } else {
        // No quick check was generated.  Put the full code here.
        // If this is not the first choice then there could be slow checks from
        // previous cases that go here when they fail.  There's no reason to
        // insist that they preload characters since the slow check we are about
        // to generate probably can't use it.
        if (i != first_normal_choice) {
          alt_gen->expects_preload = false;
          new_trace.InvalidateCurrentCharacter();
        }
        if (i < choice_count - 1) {
          new_trace.set_backtrack(&alt_gen->after);
        }
        generate_full_check_inline = true;
      }
      if (generate_full_check_inline) {
        if (new_trace.actions() != NULL) {
          new_trace.set_flush_budget(new_flush_budget);
        }
        for (int j = 0; j < guard_count; j++) {
          GenerateGuard(macro_assembler, guards->at(j), &new_trace);
        }
        alternative.node()->Emit(compiler, &new_trace);
        preload_is_current = false;
      }
      macro_assembler->Bind(&alt_gen->after);
    }
    if (greedy_loop) {
      macro_assembler->Bind(&greedy_loop_label);
      // If we have unwound to the bottom then backtrack.
      macro_assembler->CheckGreedyLoop(trace->backtrack());
      // Otherwise try the second priority at an earlier position.
      macro_assembler->AdvanceCurrentPosition(-text_length);
      macro_assembler->GoTo(&second_choice);
    }
  
    // At this point we need to generate slow checks for the alternatives where
    // the quick check was inlined.  We can recognize these because the associated
    // label was bound.
    for (int i = first_normal_choice; i < choice_count - 1; i++) {
      AlternativeGeneration* alt_gen = alt_gens.at(i);
      Trace new_trace(*current_trace);
      // If there are actions to be flushed we have to limit how many times
      // they are flushed.  Take the budget of the parent trace and distribute
      // it fairly amongst the children.
      if (new_trace.actions() != NULL) {
        new_trace.set_flush_budget(new_flush_budget);
      }
      EmitOutOfLineContinuation(compiler,
                                &new_trace,
                                alternatives_->at(i),
                                alt_gen,
                                preload_characters,
                                alt_gens.at(i + 1)->expects_preload);
    }
  }
  
  
  void ChoiceNode::EmitOutOfLineContinuation(RegExpCompiler* compiler,
                                             Trace* trace,
                                             GuardedAlternative alternative,
                                             AlternativeGeneration* alt_gen,
                                             int preload_characters,
                                             bool next_expects_preload) {
    if (!alt_gen->possible_success.is_linked()) return;
  
    RegExpMacroAssembler* macro_assembler = compiler->macro_assembler();
    macro_assembler->Bind(&alt_gen->possible_success);
    Trace out_of_line_trace(*trace);
    out_of_line_trace.set_characters_preloaded(preload_characters);
    out_of_line_trace.set_quick_check_performed(&alt_gen->quick_check_details);
    if (not_at_start_) out_of_line_trace.set_at_start(Trace::FALSE);
    ZoneList<Guard*>* guards = alternative.guards();
    int guard_count = (guards == NULL) ? 0 : guards->length();
    if (next_expects_preload) {
      Label reload_current_char;
      out_of_line_trace.set_backtrack(&reload_current_char);
      for (int j = 0; j < guard_count; j++) {
        GenerateGuard(macro_assembler, guards->at(j), &out_of_line_trace);
      }
      alternative.node()->Emit(compiler, &out_of_line_trace);
      macro_assembler->Bind(&reload_current_char);
      // Reload the current character, since the next quick check expects that.
      // We don't need to check bounds here because we only get into this
      // code through a quick check which already did the checked load.
      macro_assembler->LoadCurrentCharacter(trace->cp_offset(),
                                            NULL,
                                            false,
                                            preload_characters);
      macro_assembler->GoTo(&(alt_gen->after));
    } else {
      out_of_line_trace.set_backtrack(&(alt_gen->after));
      for (int j = 0; j < guard_count; j++) {
        GenerateGuard(macro_assembler, guards->at(j), &out_of_line_trace);
      }
      alternative.node()->Emit(compiler, &out_of_line_trace);
    }
  }
  
  
  void ActionNode::Emit(RegExpCompiler* compiler, Trace* trace) {
    RegExpMacroAssembler* assembler = compiler->macro_assembler();
    LimitResult limit_result = LimitVersions(compiler, trace);
    if (limit_result == DONE) return;
    ASSERT(limit_result == CONTINUE);
  
    RecursionCheck rc(compiler);
  
    switch (type_) {
      case STORE_POSITION: {
        Trace::DeferredCapture
            new_capture(data_.u_position_register.reg,
                        data_.u_position_register.is_capture,
                        trace);
        Trace new_trace = *trace;
        new_trace.add_action(&new_capture);
        on_success()->Emit(compiler, &new_trace);
        break;
      }
      case INCREMENT_REGISTER: {
        Trace::DeferredIncrementRegister
            new_increment(data_.u_increment_register.reg);
        Trace new_trace = *trace;
        new_trace.add_action(&new_increment);
        on_success()->Emit(compiler, &new_trace);
        break;
      }
      case SET_REGISTER: {
        Trace::DeferredSetRegister
            new_set(data_.u_store_register.reg, data_.u_store_register.value);
        Trace new_trace = *trace;
        new_trace.add_action(&new_set);
        on_success()->Emit(compiler, &new_trace);
        break;
      }
      case CLEAR_CAPTURES: {
        Trace::DeferredClearCaptures
          new_capture(Interval(data_.u_clear_captures.range_from,
                               data_.u_clear_captures.range_to));
        Trace new_trace = *trace;
        new_trace.add_action(&new_capture);
        on_success()->Emit(compiler, &new_trace);
        break;
      }
      case BEGIN_SUBMATCH:
        if (!trace->is_trivial()) {
          trace->Flush(compiler, this);
        } else {
          assembler->WriteCurrentPositionToRegister(
              data_.u_submatch.current_position_register, 0);
          assembler->WriteStackPointerToRegister(
              data_.u_submatch.stack_pointer_register);
          on_success()->Emit(compiler, trace);
        }
        break;
      case EMPTY_MATCH_CHECK: {
        int start_pos_reg = data_.u_empty_match_check.start_register;
        int stored_pos = 0;
        int rep_reg = data_.u_empty_match_check.repetition_register;
        bool has_minimum = (rep_reg != RegExpCompiler::kNoRegister);
        bool know_dist = trace->GetStoredPosition(start_pos_reg, &stored_pos);
        if (know_dist && !has_minimum && stored_pos == trace->cp_offset()) {
          // If we know we haven't advanced and there is no minimum we
          // can just backtrack immediately.
          assembler->GoTo(trace->backtrack());
        } else if (know_dist && stored_pos < trace->cp_offset()) {
          // If we know we've advanced we can generate the continuation
          // immediately.
          on_success()->Emit(compiler, trace);
        } else if (!trace->is_trivial()) {
          trace->Flush(compiler, this);
        } else {
          Label skip_empty_check;
          // If we have a minimum number of repetitions we check the current
          // number first and skip the empty check if it's not enough.
          if (has_minimum) {
            int limit = data_.u_empty_match_check.repetition_limit;
            assembler->IfRegisterLT(rep_reg, limit, &skip_empty_check);
          }
          // If the match is empty we bail out, otherwise we fall through
          // to the on-success continuation.
          assembler->IfRegisterEqPos(data_.u_empty_match_check.start_register,
                                     trace->backtrack());
          assembler->Bind(&skip_empty_check);
          on_success()->Emit(compiler, trace);
        }
        break;
      }
      case POSITIVE_SUBMATCH_SUCCESS: {
        if (!trace->is_trivial()) {
          trace->Flush(compiler, this);
          return;
        }
        assembler->ReadCurrentPositionFromRegister(
            data_.u_submatch.current_position_register);
        assembler->ReadStackPointerFromRegister(
            data_.u_submatch.stack_pointer_register);
        int clear_register_count = data_.u_submatch.clear_register_count;
        if (clear_register_count == 0) {
          on_success()->Emit(compiler, trace);
          return;
        }
        int clear_registers_from = data_.u_submatch.clear_register_from;
        Label clear_registers_backtrack;
        Trace new_trace = *trace;
        new_trace.set_backtrack(&clear_registers_backtrack);
        on_success()->Emit(compiler, &new_trace);
  
        assembler->Bind(&clear_registers_backtrack);
        int clear_registers_to = clear_registers_from + clear_register_count - 1;
        assembler->ClearRegisters(clear_registers_from, clear_registers_to);
  
        ASSERT(trace->backtrack() == NULL);
        assembler->Backtrack();
        return;
      }
      default:
        UNREACHABLE();
    }
  }
  
  
  void BackReferenceNode::Emit(RegExpCompiler* compiler, Trace* trace) {
    RegExpMacroAssembler* assembler = compiler->macro_assembler();
    if (!trace->is_trivial()) {
      trace->Flush(compiler, this);
      return;
    }
  
    LimitResult limit_result = LimitVersions(compiler, trace);
    if (limit_result == DONE) return;
    ASSERT(limit_result == CONTINUE);
  
    RecursionCheck rc(compiler);
  
    ASSERT_EQ(start_reg_ + 1, end_reg_);
    if (compiler->ignore_case()) {
      assembler->CheckNotBackReferenceIgnoreCase(start_reg_,
                                                 trace->backtrack());
    } else {
      assembler->CheckNotBackReference(start_reg_, trace->backtrack());
    }
    on_success()->Emit(compiler, trace);
  }
  
  
  // -------------------------------------------------------------------
  // Dot/dotty output
  
  
  #ifdef DEBUG
  
  
  class DotPrinter: public NodeVisitor {
   public:
    explicit DotPrinter(bool ignore_case)
        : ignore_case_(ignore_case),
          stream_(&alloc_) { }
    void PrintNode(const char* label, RegExpNode* node);
    void Visit(RegExpNode* node);
    void PrintAttributes(RegExpNode* from);
    StringStream* stream() { return &stream_; }
    void PrintOnFailure(RegExpNode* from, RegExpNode* to);
  #define DECLARE_VISIT(Type)                                          \
    virtual void Visit##Type(Type##Node* that);
  FOR_EACH_NODE_TYPE(DECLARE_VISIT)
  #undef DECLARE_VISIT
   private:
    bool ignore_case_;
    HeapStringAllocator alloc_;
    StringStream stream_;
  };
  
  
  void DotPrinter::PrintNode(const char* label, RegExpNode* node) {
    stream()->Add("digraph G {\n  graph [label=\"");
    for (int i = 0; label[i]; i++) {
      switch (label[i]) {
        case '\\':
          stream()->Add("\\\\");
          break;
        case '"':
          stream()->Add("\"");
          break;
        default:
          stream()->Put(label[i]);
          break;
      }
    }
    stream()->Add("\"];\n");
    Visit(node);
    stream()->Add("}\n");
    printf("%s", *(stream()->ToCString()));
  }
  
  
  void DotPrinter::Visit(RegExpNode* node) {
    if (node->info()->visited) return;
    node->info()->visited = true;
    node->Accept(this);
  }
  
  
  void DotPrinter::PrintOnFailure(RegExpNode* from, RegExpNode* on_failure) {
    stream()->Add("  n%p -> n%p [style=dotted];\n", from, on_failure);
    Visit(on_failure);
  }
  
  
  class TableEntryBodyPrinter {
   public:
    TableEntryBodyPrinter(StringStream* stream, ChoiceNode* choice)
        : stream_(stream), choice_(choice) { }
    void Call(uc16 from, DispatchTable::Entry entry) {
      OutSet* out_set = entry.out_set();
      for (unsigned i = 0; i < OutSet::kFirstLimit; i++) {
        if (out_set->Get(i)) {
          stream()->Add("    n%p:s%io%i -> n%p;\n",
                        choice(),
                        from,
                        i,
                        choice()->alternatives()->at(i).node());
        }
      }
    }
   private:
    StringStream* stream() { return stream_; }
    ChoiceNode* choice() { return choice_; }
    StringStream* stream_;
    ChoiceNode* choice_;
  };
  
  
  class TableEntryHeaderPrinter {
   public:
    explicit TableEntryHeaderPrinter(StringStream* stream)
        : first_(true), stream_(stream) { }
    void Call(uc16 from, DispatchTable::Entry entry) {
      if (first_) {
        first_ = false;
      } else {
        stream()->Add("|");
      }
      stream()->Add("{\\%k-\\%k|{", from, entry.to());
      OutSet* out_set = entry.out_set();
      int priority = 0;
      for (unsigned i = 0; i < OutSet::kFirstLimit; i++) {
        if (out_set->Get(i)) {
          if (priority > 0) stream()->Add("|");
          stream()->Add("<s%io%i> %i", from, i, priority);
          priority++;
        }
      }
      stream()->Add("}}");
    }
  
   private:
    bool first_;
    StringStream* stream() { return stream_; }
    StringStream* stream_;
  };
  
  
  class AttributePrinter {
   public:
    explicit AttributePrinter(DotPrinter* out)
        : out_(out), first_(true) { }
    void PrintSeparator() {
      if (first_) {
        first_ = false;
      } else {
        out_->stream()->Add("|");
      }
    }
    void PrintBit(const char* name, bool value) {
      if (!value) return;
      PrintSeparator();
      out_->stream()->Add("{%s}", name);
    }
    void PrintPositive(const char* name, int value) {
      if (value < 0) return;
      PrintSeparator();
      out_->stream()->Add("{%s|%x}", name, value);
    }
   private:
    DotPrinter* out_;
    bool first_;
  };
  
  
  void DotPrinter::PrintAttributes(RegExpNode* that) {
    stream()->Add("  a%p [shape=Mrecord, color=grey, fontcolor=grey, "
                  "margin=0.1, fontsize=10, label=\"{",
                  that);
    AttributePrinter printer(this);
    NodeInfo* info = that->info();
    printer.PrintBit("NI", info->follows_newline_interest);
    printer.PrintBit("WI", info->follows_word_interest);
    printer.PrintBit("SI", info->follows_start_interest);
    Label* label = that->label();
    if (label->is_bound())
      printer.PrintPositive("@", label->pos());
    stream()->Add("}\"];\n");
    stream()->Add("  a%p -> n%p [style=dashed, color=grey, "
                  "arrowhead=none];\n", that, that);
  }
  
  
  static const bool kPrintDispatchTable = false;
  void DotPrinter::VisitChoice(ChoiceNode* that) {
    if (kPrintDispatchTable) {
      stream()->Add("  n%p [shape=Mrecord, label=\"", that);
      TableEntryHeaderPrinter header_printer(stream());
      that->GetTable(ignore_case_)->ForEach(&header_printer);
      stream()->Add("\"]\n", that);
      PrintAttributes(that);
      TableEntryBodyPrinter body_printer(stream(), that);
      that->GetTable(ignore_case_)->ForEach(&body_printer);
    } else {
      stream()->Add("  n%p [shape=Mrecord, label=\"?\"];\n", that);
      for (int i = 0; i < that->alternatives()->length(); i++) {
        GuardedAlternative alt = that->alternatives()->at(i);
        stream()->Add("  n%p -> n%p;\n", that, alt.node());
      }
    }
    for (int i = 0; i < that->alternatives()->length(); i++) {
      GuardedAlternative alt = that->alternatives()->at(i);
      alt.node()->Accept(this);
    }
  }
  
  
  void DotPrinter::VisitText(TextNode* that) {
    stream()->Add("  n%p [label=\"", that);
    for (int i = 0; i < that->elements()->length(); i++) {
      if (i > 0) stream()->Add(" ");
      TextElement elm = that->elements()->at(i);
      switch (elm.type) {
        case TextElement::ATOM: {
          stream()->Add("'%w'", elm.data.u_atom->data());
          break;
        }
        case TextElement::CHAR_CLASS: {
          RegExpCharacterClass* node = elm.data.u_char_class;
          stream()->Add("[");
          if (node->is_negated())
            stream()->Add("^");
          for (int j = 0; j < node->ranges()->length(); j++) {
            CharacterRange range = node->ranges()->at(j);
            stream()->Add("%k-%k", range.from(), range.to());
          }
          stream()->Add("]");
          break;
        }
        default:
          UNREACHABLE();
      }
    }
    stream()->Add("\", shape=box, peripheries=2];\n");
    PrintAttributes(that);
    stream()->Add("  n%p -> n%p;\n", that, that->on_success());
    Visit(that->on_success());
  }
  
  
  void DotPrinter::VisitBackReference(BackReferenceNode* that) {
    stream()->Add("  n%p [label=\"$%i..$%i\", shape=doubleoctagon];\n",
                  that,
                  that->start_register(),
                  that->end_register());
    PrintAttributes(that);
    stream()->Add("  n%p -> n%p;\n", that, that->on_success());
    Visit(that->on_success());
  }
  
  
  void DotPrinter::VisitEnd(EndNode* that) {
    stream()->Add("  n%p [style=bold, shape=point];\n", that);
    PrintAttributes(that);
  }
  
  
  void DotPrinter::VisitAssertion(AssertionNode* that) {
    stream()->Add("  n%p [", that);
    switch (that->type()) {
      case AssertionNode::AT_END:
        stream()->Add("label=\"$\", shape=septagon");
        break;
      case AssertionNode::AT_START:
        stream()->Add("label=\"^\", shape=septagon");
        break;
      case AssertionNode::AT_BOUNDARY:
        stream()->Add("label=\"\\b\", shape=septagon");
        break;
      case AssertionNode::AT_NON_BOUNDARY:
        stream()->Add("label=\"\\B\", shape=septagon");
        break;
      case AssertionNode::AFTER_NEWLINE:
        stream()->Add("label=\"(?<=\\n)\", shape=septagon");
        break;
      case AssertionNode::AFTER_WORD_CHARACTER:
        stream()->Add("label=\"(?<=\\w)\", shape=septagon");
        break;
      case AssertionNode::AFTER_NONWORD_CHARACTER:
        stream()->Add("label=\"(?<=\\W)\", shape=septagon");
        break;
    }
    stream()->Add("];\n");
    PrintAttributes(that);
    RegExpNode* successor = that->on_success();
    stream()->Add("  n%p -> n%p;\n", that, successor);
    Visit(successor);
  }
  
  
  void DotPrinter::VisitAction(ActionNode* that) {
    stream()->Add("  n%p [", that);
    switch (that->type_) {
      case ActionNode::SET_REGISTER:
        stream()->Add("label=\"$%i:=%i\", shape=octagon",
                      that->data_.u_store_register.reg,
                      that->data_.u_store_register.value);
        break;
      case ActionNode::INCREMENT_REGISTER:
        stream()->Add("label=\"$%i++\", shape=octagon",
                      that->data_.u_increment_register.reg);
        break;
      case ActionNode::STORE_POSITION:
        stream()->Add("label=\"$%i:=$pos\", shape=octagon",
                      that->data_.u_position_register.reg);
        break;
      case ActionNode::BEGIN_SUBMATCH:
        stream()->Add("label=\"$%i:=$pos,begin\", shape=septagon",
                      that->data_.u_submatch.current_position_register);
        break;
      case ActionNode::POSITIVE_SUBMATCH_SUCCESS:
        stream()->Add("label=\"escape\", shape=septagon");
        break;
      case ActionNode::EMPTY_MATCH_CHECK:
        stream()->Add("label=\"$%i=$pos?,$%i<%i?\", shape=septagon",
                      that->data_.u_empty_match_check.start_register,
                      that->data_.u_empty_match_check.repetition_register,
                      that->data_.u_empty_match_check.repetition_limit);
        break;
      case ActionNode::CLEAR_CAPTURES: {
        stream()->Add("label=\"clear $%i to $%i\", shape=septagon",
                      that->data_.u_clear_captures.range_from,
                      that->data_.u_clear_captures.range_to);
        break;
      }
    }
    stream()->Add("];\n");
    PrintAttributes(that);
    RegExpNode* successor = that->on_success();
    stream()->Add("  n%p -> n%p;\n", that, successor);
    Visit(successor);
  }
  
  
  class DispatchTableDumper {
   public:
    explicit DispatchTableDumper(StringStream* stream) : stream_(stream) { }
    void Call(uc16 key, DispatchTable::Entry entry);
    StringStream* stream() { return stream_; }
   private:
    StringStream* stream_;
  };
  
  
  void DispatchTableDumper::Call(uc16 key, DispatchTable::Entry entry) {
    stream()->Add("[%k-%k]: {", key, entry.to());
    OutSet* set = entry.out_set();
    bool first = true;
    for (unsigned i = 0; i < OutSet::kFirstLimit; i++) {
      if (set->Get(i)) {
        if (first) {
          first = false;
        } else {
          stream()->Add(", ");
        }
        stream()->Add("%i", i);
      }
    }
    stream()->Add("}\n");
  }
  
  
  void DispatchTable::Dump() {
    HeapStringAllocator alloc;
    StringStream stream(&alloc);
    DispatchTableDumper dumper(&stream);
    tree()->ForEach(&dumper);
    OS::PrintError("%s", *stream.ToCString());
  }
  
  
  void RegExpEngine::DotPrint(const char* label,
                              RegExpNode* node,
                              bool ignore_case) {
    DotPrinter printer(ignore_case);
    printer.PrintNode(label, node);
  }
  
  
  #endif  // DEBUG
  
  
  // -------------------------------------------------------------------
  // Tree to graph conversion
  
  static const uc16 kSpaceRanges[] = { 0x0009, 0x000D, 0x0020, 0x0020, 0x00A0,
      0x00A0, 0x1680, 0x1680, 0x180E, 0x180E, 0x2000, 0x200A, 0x2028, 0x2029,
      0x202F, 0x202F, 0x205F, 0x205F, 0x3000, 0x3000, 0xFEFF, 0xFEFF };
  static const int kSpaceRangeCount = ARRAY_SIZE(kSpaceRanges);
  
  static const uc16 kWordRanges[] = { '0', '9', 'A', 'Z', '_', '_', 'a', 'z' };
  static const int kWordRangeCount = ARRAY_SIZE(kWordRanges);
  
  static const uc16 kDigitRanges[] = { '0', '9' };
  static const int kDigitRangeCount = ARRAY_SIZE(kDigitRanges);
  
  static const uc16 kLineTerminatorRanges[] = { 0x000A, 0x000A, 0x000D, 0x000D,
      0x2028, 0x2029 };
  static const int kLineTerminatorRangeCount = ARRAY_SIZE(kLineTerminatorRanges);
  
  RegExpNode* RegExpAtom::ToNode(RegExpCompiler* compiler,
                                 RegExpNode* on_success) {
    ZoneList<TextElement>* elms = new ZoneList<TextElement>(1);
    elms->Add(TextElement::Atom(this));
    return new TextNode(elms, on_success);
  }
  
  
  RegExpNode* RegExpText::ToNode(RegExpCompiler* compiler,
                                 RegExpNode* on_success) {
    return new TextNode(elements(), on_success);
  }
  
  static bool CompareInverseRanges(ZoneList<CharacterRange>* ranges,
                                   const uc16* special_class,
                                   int length) {
    ASSERT(ranges->length() != 0);
    ASSERT(length != 0);
    ASSERT(special_class[0] != 0);
    if (ranges->length() != (length >> 1) + 1) {
      return false;
    }
    CharacterRange range = ranges->at(0);
    if (range.from() != 0) {
      return false;
    }
    for (int i = 0; i < length; i += 2) {
      if (special_class[i] != (range.to() + 1)) {
        return false;
      }
      range = ranges->at((i >> 1) + 1);
      if (special_class[i+1] != range.from() - 1) {
        return false;
      }
    }
    if (range.to() != 0xffff) {
      return false;
    }
    return true;
  }
  
  
  static bool CompareRanges(ZoneList<CharacterRange>* ranges,
                            const uc16* special_class,
                            int length) {
    if (ranges->length() * 2 != length) {
      return false;
    }
    for (int i = 0; i < length; i += 2) {
      CharacterRange range = ranges->at(i >> 1);
      if (range.from() != special_class[i] || range.to() != special_class[i+1]) {
        return false;
      }
    }
    return true;
  }
  
  
  bool RegExpCharacterClass::is_standard() {
    // TODO(lrn): Remove need for this function, by not throwing away information
    // along the way.
    if (is_negated_) {
      return false;
    }
    if (set_.is_standard()) {
      return true;
    }
    if (CompareRanges(set_.ranges(), kSpaceRanges, kSpaceRangeCount)) {
      set_.set_standard_set_type('s');
      return true;
    }
    if (CompareInverseRanges(set_.ranges(), kSpaceRanges, kSpaceRangeCount)) {
      set_.set_standard_set_type('S');
      return true;
    }
    if (CompareInverseRanges(set_.ranges(),
                             kLineTerminatorRanges,
                             kLineTerminatorRangeCount)) {
      set_.set_standard_set_type('.');
      return true;
    }
    if (CompareRanges(set_.ranges(),
                      kLineTerminatorRanges,
                      kLineTerminatorRangeCount)) {
      set_.set_standard_set_type('n');
      return true;
    }
    if (CompareRanges(set_.ranges(), kWordRanges, kWordRangeCount)) {
      set_.set_standard_set_type('w');
      return true;
    }
    if (CompareInverseRanges(set_.ranges(), kWordRanges, kWordRangeCount)) {
      set_.set_standard_set_type('W');
      return true;
    }
    return false;
  }
  
  
  RegExpNode* RegExpCharacterClass::ToNode(RegExpCompiler* compiler,
                                           RegExpNode* on_success) {
    return new TextNode(this, on_success);
  }
  
  
  RegExpNode* RegExpDisjunction::ToNode(RegExpCompiler* compiler,
                                        RegExpNode* on_success) {
    ZoneList<RegExpTree*>* alternatives = this->alternatives();
    int length = alternatives->length();
    ChoiceNode* result = new ChoiceNode(length);
    for (int i = 0; i < length; i++) {
      GuardedAlternative alternative(alternatives->at(i)->ToNode(compiler,
                                                                 on_success));
      result->AddAlternative(alternative);
    }
    return result;
  }
  
  
  RegExpNode* RegExpQuantifier::ToNode(RegExpCompiler* compiler,
                                       RegExpNode* on_success) {
    return ToNode(min(),
                  max(),
                  is_greedy(),
                  body(),
                  compiler,
                  on_success);
  }
  
  
  // Scoped object to keep track of how much we unroll quantifier loops in the
  // regexp graph generator.
  class RegExpExpansionLimiter {
   public:
    static const int kMaxExpansionFactor = 6;
    RegExpExpansionLimiter(RegExpCompiler* compiler, int factor)
        : compiler_(compiler),
          saved_expansion_factor_(compiler->current_expansion_factor()),
          ok_to_expand_(saved_expansion_factor_ <= kMaxExpansionFactor) {
      ASSERT(factor > 0);
      if (ok_to_expand_) {
        if (factor > kMaxExpansionFactor) {
          // Avoid integer overflow of the current expansion factor.
          ok_to_expand_ = false;
          compiler->set_current_expansion_factor(kMaxExpansionFactor + 1);
        } else {
          int new_factor = saved_expansion_factor_ * factor;
          ok_to_expand_ = (new_factor <= kMaxExpansionFactor);
          compiler->set_current_expansion_factor(new_factor);
        }
      }
    }
  
    ~RegExpExpansionLimiter() {
      compiler_->set_current_expansion_factor(saved_expansion_factor_);
    }
  
    bool ok_to_expand() { return ok_to_expand_; }
  
   private:
    RegExpCompiler* compiler_;
    int saved_expansion_factor_;
    bool ok_to_expand_;
  
    DISALLOW_IMPLICIT_CONSTRUCTORS(RegExpExpansionLimiter);
  };
  
  
  RegExpNode* RegExpQuantifier::ToNode(int min,
                                       int max,
                                       bool is_greedy,
                                       RegExpTree* body,
                                       RegExpCompiler* compiler,
                                       RegExpNode* on_success,
                                       bool not_at_start) {
    // x{f, t} becomes this:
    //
    //             (r++)<-.
    //               |     `
    //               |     (x)
    //               v     ^
    //      (r=0)-->(?)---/ [if r < t]
    //               |
    //   [if r >= f] \----> ...
    //
  
    // 15.10.2.5 RepeatMatcher algorithm.
    // The parser has already eliminated the case where max is 0.  In the case
    // where max_match is zero the parser has removed the quantifier if min was
    // > 0 and removed the atom if min was 0.  See AddQuantifierToAtom.
  
    // If we know that we cannot match zero length then things are a little
    // simpler since we don't need to make the special zero length match check
    // from step 2.1.  If the min and max are small we can unroll a little in
    // this case.
    static const int kMaxUnrolledMinMatches = 3;  // Unroll (foo)+ and (foo){3,}
    static const int kMaxUnrolledMaxMatches = 3;  // Unroll (foo)? and (foo){x,3}
    if (max == 0) return on_success;  // This can happen due to recursion.
    bool body_can_be_empty = (body->min_match() == 0);
    int body_start_reg = RegExpCompiler::kNoRegister;
    Interval capture_registers = body->CaptureRegisters();
    bool needs_capture_clearing = !capture_registers.is_empty();
    if (body_can_be_empty) {
      body_start_reg = compiler->AllocateRegister();
    } else if (FLAG_regexp_optimization && !needs_capture_clearing) {
      // Only unroll if there are no captures and the body can't be
      // empty.
      {
        RegExpExpansionLimiter limiter(
            compiler, min + ((max != min) ? 1 : 0));
        if (min > 0 && min <= kMaxUnrolledMinMatches && limiter.ok_to_expand()) {
          int new_max = (max == kInfinity) ? max : max - min;
          // Recurse once to get the loop or optional matches after the fixed
          // ones.
          RegExpNode* answer = ToNode(
              0, new_max, is_greedy, body, compiler, on_success, true);
          // Unroll the forced matches from 0 to min.  This can cause chains of
          // TextNodes (which the parser does not generate).  These should be
          // combined if it turns out they hinder good code generation.
          for (int i = 0; i < min; i++) {
            answer = body->ToNode(compiler, answer);
          }
          return answer;
        }
      }
      if (max <= kMaxUnrolledMaxMatches && min == 0) {
        ASSERT(max > 0);  // Due to the 'if' above.
        RegExpExpansionLimiter limiter(compiler, max);
        if (limiter.ok_to_expand()) {
          // Unroll the optional matches up to max.
          RegExpNode* answer = on_success;
          for (int i = 0; i < max; i++) {
            ChoiceNode* alternation = new ChoiceNode(2);
            if (is_greedy) {
              alternation->AddAlternative(
                  GuardedAlternative(body->ToNode(compiler, answer)));
              alternation->AddAlternative(GuardedAlternative(on_success));
            } else {
              alternation->AddAlternative(GuardedAlternative(on_success));
              alternation->AddAlternative(
                  GuardedAlternative(body->ToNode(compiler, answer)));
            }
            answer = alternation;
            if (not_at_start) alternation->set_not_at_start();
          }
          return answer;
        }
      }
    }
    bool has_min = min > 0;
    bool has_max = max < RegExpTree::kInfinity;
    bool needs_counter = has_min || has_max;
    int reg_ctr = needs_counter
        ? compiler->AllocateRegister()
        : RegExpCompiler::kNoRegister;
    LoopChoiceNode* center = new LoopChoiceNode(body->min_match() == 0);
    if (not_at_start) center->set_not_at_start();
    RegExpNode* loop_return = needs_counter
        ? static_cast<RegExpNode*>(ActionNode::IncrementRegister(reg_ctr, center))
        : static_cast<RegExpNode*>(center);
    if (body_can_be_empty) {
      // If the body can be empty we need to check if it was and then
      // backtrack.
      loop_return = ActionNode::EmptyMatchCheck(body_start_reg,
                                                reg_ctr,
                                                min,
                                                loop_return);
    }
    RegExpNode* body_node = body->ToNode(compiler, loop_return);
    if (body_can_be_empty) {
      // If the body can be empty we need to store the start position
      // so we can bail out if it was empty.
      body_node = ActionNode::StorePosition(body_start_reg, false, body_node);
    }
    if (needs_capture_clearing) {
      // Before entering the body of this loop we need to clear captures.
      body_node = ActionNode::ClearCaptures(capture_registers, body_node);
    }
    GuardedAlternative body_alt(body_node);
    if (has_max) {
      Guard* body_guard = new Guard(reg_ctr, Guard::LT, max);
      body_alt.AddGuard(body_guard);
    }
    GuardedAlternative rest_alt(on_success);
    if (has_min) {
      Guard* rest_guard = new Guard(reg_ctr, Guard::GEQ, min);
      rest_alt.AddGuard(rest_guard);
    }
    if (is_greedy) {
      center->AddLoopAlternative(body_alt);
      center->AddContinueAlternative(rest_alt);
    } else {
      center->AddContinueAlternative(rest_alt);
      center->AddLoopAlternative(body_alt);
    }
    if (needs_counter) {
      return ActionNode::SetRegister(reg_ctr, 0, center);
    } else {
      return center;
    }
  }
  
  
  RegExpNode* RegExpAssertion::ToNode(RegExpCompiler* compiler,
                                      RegExpNode* on_success) {
    NodeInfo info;
    switch (type()) {
      case START_OF_LINE:
        return AssertionNode::AfterNewline(on_success);
      case START_OF_INPUT:
        return AssertionNode::AtStart(on_success);
      case BOUNDARY:
        return AssertionNode::AtBoundary(on_success);
      case NON_BOUNDARY:
        return AssertionNode::AtNonBoundary(on_success);
      case END_OF_INPUT:
        return AssertionNode::AtEnd(on_success);
      case END_OF_LINE: {
        // Compile $ in multiline regexps as an alternation with a positive
        // lookahead in one side and an end-of-input on the other side.
        // We need two registers for the lookahead.
        int stack_pointer_register = compiler->AllocateRegister();
        int position_register = compiler->AllocateRegister();
        // The ChoiceNode to distinguish between a newline and end-of-input.
        ChoiceNode* result = new ChoiceNode(2);
        // Create a newline atom.
        ZoneList<CharacterRange>* newline_ranges =
            new ZoneList<CharacterRange>(3);
        CharacterRange::AddClassEscape('n', newline_ranges);
        RegExpCharacterClass* newline_atom = new RegExpCharacterClass('n');
        TextNode* newline_matcher = new TextNode(
           newline_atom,
           ActionNode::PositiveSubmatchSuccess(stack_pointer_register,
                                               position_register,
                                               0,  // No captures inside.
                                               -1,  // Ignored if no captures.
                                               on_success));
        // Create an end-of-input matcher.
        RegExpNode* end_of_line = ActionNode::BeginSubmatch(
            stack_pointer_register,
            position_register,
            newline_matcher);
        // Add the two alternatives to the ChoiceNode.
        GuardedAlternative eol_alternative(end_of_line);
        result->AddAlternative(eol_alternative);
        GuardedAlternative end_alternative(AssertionNode::AtEnd(on_success));
        result->AddAlternative(end_alternative);
        return result;
      }
      default:
        UNREACHABLE();
    }
    return on_success;
  }
  
  
  RegExpNode* RegExpBackReference::ToNode(RegExpCompiler* compiler,
                                          RegExpNode* on_success) {
    return new BackReferenceNode(RegExpCapture::StartRegister(index()),
                                 RegExpCapture::EndRegister(index()),
                                 on_success);
  }
  
  
  RegExpNode* RegExpEmpty::ToNode(RegExpCompiler* compiler,
                                  RegExpNode* on_success) {
    return on_success;
  }
  
  
  RegExpNode* RegExpLookahead::ToNode(RegExpCompiler* compiler,
                                      RegExpNode* on_success) {
    int stack_pointer_register = compiler->AllocateRegister();
    int position_register = compiler->AllocateRegister();
  
    const int registers_per_capture = 2;
    const int register_of_first_capture = 2;
    int register_count = capture_count_ * registers_per_capture;
    int register_start =
      register_of_first_capture + capture_from_ * registers_per_capture;
  
    RegExpNode* success;
    if (is_positive()) {
      RegExpNode* node = ActionNode::BeginSubmatch(
          stack_pointer_register,
          position_register,
          body()->ToNode(
              compiler,
              ActionNode::PositiveSubmatchSuccess(stack_pointer_register,
                                                  position_register,
                                                  register_count,
                                                  register_start,
                                                  on_success)));
      return node;
    } else {
      // We use a ChoiceNode for a negative lookahead because it has most of
      // the characteristics we need.  It has the body of the lookahead as its
      // first alternative and the expression after the lookahead of the second
      // alternative.  If the first alternative succeeds then the
      // NegativeSubmatchSuccess will unwind the stack including everything the
      // choice node set up and backtrack.  If the first alternative fails then
      // the second alternative is tried, which is exactly the desired result
      // for a negative lookahead.  The NegativeLookaheadChoiceNode is a special
      // ChoiceNode that knows to ignore the first exit when calculating quick
      // checks.
      GuardedAlternative body_alt(
          body()->ToNode(
              compiler,
              success = new NegativeSubmatchSuccess(stack_pointer_register,
                                                    position_register,
                                                    register_count,
                                                    register_start)));
      ChoiceNode* choice_node =
          new NegativeLookaheadChoiceNode(body_alt,
                                          GuardedAlternative(on_success));
      return ActionNode::BeginSubmatch(stack_pointer_register,
                                       position_register,
                                       choice_node);
    }
  }
  
  
  RegExpNode* RegExpCapture::ToNode(RegExpCompiler* compiler,
                                    RegExpNode* on_success) {
    return ToNode(body(), index(), compiler, on_success);
  }
  
  
  RegExpNode* RegExpCapture::ToNode(RegExpTree* body,
                                    int index,
                                    RegExpCompiler* compiler,
                                    RegExpNode* on_success) {
    int start_reg = RegExpCapture::StartRegister(index);
    int end_reg = RegExpCapture::EndRegister(index);
    RegExpNode* store_end = ActionNode::StorePosition(end_reg, true, on_success);
    RegExpNode* body_node = body->ToNode(compiler, store_end);
    return ActionNode::StorePosition(start_reg, true, body_node);
  }
  
  
  RegExpNode* RegExpAlternative::ToNode(RegExpCompiler* compiler,
                                        RegExpNode* on_success) {
    ZoneList<RegExpTree*>* children = nodes();
    RegExpNode* current = on_success;
    for (int i = children->length() - 1; i >= 0; i--) {
      current = children->at(i)->ToNode(compiler, current);
    }
    return current;
  }
  
  
  static void AddClass(const uc16* elmv,
                       int elmc,
                       ZoneList<CharacterRange>* ranges) {
    for (int i = 0; i < elmc; i += 2) {
      ASSERT(elmv[i] <= elmv[i + 1]);
      ranges->Add(CharacterRange(elmv[i], elmv[i + 1]));
    }
  }
  
  
  static void AddClassNegated(const uc16 *elmv,
                              int elmc,
                              ZoneList<CharacterRange>* ranges) {
    ASSERT(elmv[0] != 0x0000);
    ASSERT(elmv[elmc-1] != String::kMaxUC16CharCode);
    uc16 last = 0x0000;
    for (int i = 0; i < elmc; i += 2) {
      ASSERT(last <= elmv[i] - 1);
      ASSERT(elmv[i] <= elmv[i + 1]);
      ranges->Add(CharacterRange(last, elmv[i] - 1));
      last = elmv[i + 1] + 1;
    }
    ranges->Add(CharacterRange(last, String::kMaxUC16CharCode));
  }
  
  
  void CharacterRange::AddClassEscape(uc16 type,
                                      ZoneList<CharacterRange>* ranges) {
    switch (type) {
      case 's':
        AddClass(kSpaceRanges, kSpaceRangeCount, ranges);
        break;
      case 'S':
        AddClassNegated(kSpaceRanges, kSpaceRangeCount, ranges);
        break;
      case 'w':
        AddClass(kWordRanges, kWordRangeCount, ranges);
        break;
      case 'W':
        AddClassNegated(kWordRanges, kWordRangeCount, ranges);
        break;
      case 'd':
        AddClass(kDigitRanges, kDigitRangeCount, ranges);
        break;
      case 'D':
        AddClassNegated(kDigitRanges, kDigitRangeCount, ranges);
        break;
      case '.':
        AddClassNegated(kLineTerminatorRanges,
                        kLineTerminatorRangeCount,
                        ranges);
        break;
      // This is not a character range as defined by the spec but a
      // convenient shorthand for a character class that matches any
      // character.
      case '*':
        ranges->Add(CharacterRange::Everything());
        break;
      // This is the set of characters matched by the $ and ^ symbols
      // in multiline mode.
      case 'n':
        AddClass(kLineTerminatorRanges,
                 kLineTerminatorRangeCount,
                 ranges);
        break;
      default:
        UNREACHABLE();
    }
  }
  
  
  Vector<const uc16> CharacterRange::GetWordBounds() {
    return Vector<const uc16>(kWordRanges, kWordRangeCount);
  }
  
  
  class CharacterRangeSplitter {
   public:
    CharacterRangeSplitter(ZoneList<CharacterRange>** included,
                            ZoneList<CharacterRange>** excluded)
        : included_(included),
          excluded_(excluded) { }
    void Call(uc16 from, DispatchTable::Entry entry);
  
    static const int kInBase = 0;
    static const int kInOverlay = 1;
  
   private:
    ZoneList<CharacterRange>** included_;
    ZoneList<CharacterRange>** excluded_;
  };
  
  
  void CharacterRangeSplitter::Call(uc16 from, DispatchTable::Entry entry) {
    if (!entry.out_set()->Get(kInBase)) return;
    ZoneList<CharacterRange>** target = entry.out_set()->Get(kInOverlay)
      ? included_
      : excluded_;
    if (*target == NULL) *target = new ZoneList<CharacterRange>(2);
    (*target)->Add(CharacterRange(entry.from(), entry.to()));
  }
  
  
  void CharacterRange::Split(ZoneList<CharacterRange>* base,
                             Vector<const uc16> overlay,
                             ZoneList<CharacterRange>** included,
                             ZoneList<CharacterRange>** excluded) {
    ASSERT_EQ(NULL, *included);
    ASSERT_EQ(NULL, *excluded);
    DispatchTable table;
    for (int i = 0; i < base->length(); i++)
      table.AddRange(base->at(i), CharacterRangeSplitter::kInBase);
    for (int i = 0; i < overlay.length(); i += 2) {
      table.AddRange(CharacterRange(overlay[i], overlay[i+1]),
                     CharacterRangeSplitter::kInOverlay);
    }
    CharacterRangeSplitter callback(included, excluded);
    table.ForEach(&callback);
  }
  
  
  void CharacterRange::AddCaseEquivalents(ZoneList<CharacterRange>* ranges,
                                          bool is_ascii) {
    Isolate* isolate = Isolate::Current();
    uc16 bottom = from();
    uc16 top = to();
    if (is_ascii) {
      if (bottom > String::kMaxAsciiCharCode) return;
      if (top > String::kMaxAsciiCharCode) top = String::kMaxAsciiCharCode;
    }
    unibrow::uchar chars[unibrow::Ecma262UnCanonicalize::kMaxWidth];
    if (top == bottom) {
      // If this is a singleton we just expand the one character.
      int length = isolate->jsregexp_uncanonicalize()->get(bottom, '\0', chars);
      for (int i = 0; i < length; i++) {
        uc32 chr = chars[i];
        if (chr != bottom) {
          ranges->Add(CharacterRange::Singleton(chars[i]));
        }
      }
    } else {
      // If this is a range we expand the characters block by block,
      // expanding contiguous subranges (blocks) one at a time.
      // The approach is as follows.  For a given start character we
      // look up the remainder of the block that contains it (represented
      // by the end point), for instance we find 'z' if the character
      // is 'c'.  A block is characterized by the property
      // that all characters uncanonicalize in the same way, except that
      // each entry in the result is incremented by the distance from the first
      // element.  So a-z is a block because 'a' uncanonicalizes to ['a', 'A'] and
      // the k'th letter uncanonicalizes to ['a' + k, 'A' + k].
      // Once we've found the end point we look up its uncanonicalization
      // and produce a range for each element.  For instance for [c-f]
      // we look up ['z', 'Z'] and produce [c-f] and [C-F].  We then only
      // add a range if it is not already contained in the input, so [c-f]
      // will be skipped but [C-F] will be added.  If this range is not
      // completely contained in a block we do this for all the blocks
      // covered by the range (handling characters that is not in a block
      // as a "singleton block").
      unibrow::uchar range[unibrow::Ecma262UnCanonicalize::kMaxWidth];
      int pos = bottom;
      while (pos < top) {
        int length = isolate->jsregexp_canonrange()->get(pos, '\0', range);
        uc16 block_end;
        if (length == 0) {
          block_end = pos;
        } else {
          ASSERT_EQ(1, length);
          block_end = range[0];
        }
        int end = (block_end > top) ? top : block_end;
        length = isolate->jsregexp_uncanonicalize()->get(block_end, '\0', range);
        for (int i = 0; i < length; i++) {
          uc32 c = range[i];
          uc16 range_from = c - (block_end - pos);
          uc16 range_to = c - (block_end - end);
          if (!(bottom <= range_from && range_to <= top)) {
            ranges->Add(CharacterRange(range_from, range_to));
          }
        }
        pos = end + 1;
      }
    }
  }
  
  
  bool CharacterRange::IsCanonical(ZoneList<CharacterRange>* ranges) {
    ASSERT_NOT_NULL(ranges);
    int n = ranges->length();
    if (n <= 1) return true;
    int max = ranges->at(0).to();
    for (int i = 1; i < n; i++) {
      CharacterRange next_range = ranges->at(i);
      if (next_range.from() <= max + 1) return false;
      max = next_range.to();
    }
    return true;
  }
  
  SetRelation CharacterRange::WordCharacterRelation(
      ZoneList<CharacterRange>* range) {
    ASSERT(IsCanonical(range));
    int i = 0;  // Word character range index.
    int j = 0;  // Argument range index.
    ASSERT_NE(0, kWordRangeCount);
    SetRelation result;
    if (range->length() == 0) {
      result.SetElementsInSecondSet();
      return result;
    }
    CharacterRange argument_range = range->at(0);
    CharacterRange word_range = CharacterRange(kWordRanges[0], kWordRanges[1]);
    while (i < kWordRangeCount && j < range->length()) {
      // Check the two ranges for the five cases:
      // - no overlap.
      // - partial overlap (there are elements in both ranges that isn't
      //   in the other, and there are also elements that are in both).
      // - argument range entirely inside word range.
      // - word range entirely inside argument range.
      // - ranges are completely equal.
  
      // First check for no overlap. The earlier range is not in the other set.
      if (argument_range.from() > word_range.to()) {
        // Ranges are disjoint. The earlier word range contains elements that
        // cannot be in the argument set.
        result.SetElementsInSecondSet();
      } else if (word_range.from() > argument_range.to()) {
        // Ranges are disjoint. The earlier argument range contains elements that
        // cannot be in the word set.
        result.SetElementsInFirstSet();
      } else if (word_range.from() <= argument_range.from() &&
                 word_range.to() >= argument_range.from()) {
        result.SetElementsInBothSets();
        // argument range completely inside word range.
        if (word_range.from() < argument_range.from() ||
            word_range.to() > argument_range.from()) {
          result.SetElementsInSecondSet();
        }
      } else if (word_range.from() >= argument_range.from() &&
                 word_range.to() <= argument_range.from()) {
        result.SetElementsInBothSets();
        result.SetElementsInFirstSet();
      } else {
        // There is overlap, and neither is a subrange of the other
        result.SetElementsInFirstSet();
        result.SetElementsInSecondSet();
        result.SetElementsInBothSets();
      }
      if (result.NonTrivialIntersection()) {
        // The result is as (im)precise as we can possibly make it.
        return result;
      }
      // Progress the range(s) with minimal to-character.
      uc16 word_to = word_range.to();
      uc16 argument_to = argument_range.to();
      if (argument_to <= word_to) {
        j++;
        if (j < range->length()) {
          argument_range = range->at(j);
        }
      }
      if (word_to <= argument_to) {
        i += 2;
        if (i < kWordRangeCount) {
          word_range = CharacterRange(kWordRanges[i], kWordRanges[i + 1]);
        }
      }
    }
    // Check if anything wasn't compared in the loop.
    if (i < kWordRangeCount) {
      // word range contains something not in argument range.
      result.SetElementsInSecondSet();
    } else if (j < range->length()) {
      // Argument range contains something not in word range.
      result.SetElementsInFirstSet();
    }
  
    return result;
  }
  
  
  ZoneList<CharacterRange>* CharacterSet::ranges() {
    if (ranges_ == NULL) {
      ranges_ = new ZoneList<CharacterRange>(2);
      CharacterRange::AddClassEscape(standard_set_type_, ranges_);
    }
    return ranges_;
  }
  
  
  // Move a number of elements in a zonelist to another position
  // in the same list. Handles overlapping source and target areas.
  static void MoveRanges(ZoneList<CharacterRange>* list,
                         int from,
                         int to,
                         int count) {
    // Ranges are potentially overlapping.
    if (from < to) {
      for (int i = count - 1; i >= 0; i--) {
        list->at(to + i) = list->at(from + i);
      }
    } else {
      for (int i = 0; i < count; i++) {
        list->at(to + i) = list->at(from + i);
      }
    }
  }
  
  
  static int InsertRangeInCanonicalList(ZoneList<CharacterRange>* list,
                                        int count,
                                        CharacterRange insert) {
    // Inserts a range into list[0..count[, which must be sorted
    // by from value and non-overlapping and non-adjacent, using at most
    // list[0..count] for the result. Returns the number of resulting
    // canonicalized ranges. Inserting a range may collapse existing ranges into
    // fewer ranges, so the return value can be anything in the range 1..count+1.
    uc16 from = insert.from();
    uc16 to = insert.to();
    int start_pos = 0;
    int end_pos = count;
    for (int i = count - 1; i >= 0; i--) {
      CharacterRange current = list->at(i);
      if (current.from() > to + 1) {
        end_pos = i;
      } else if (current.to() + 1 < from) {
        start_pos = i + 1;
        break;
      }
    }
  
    // Inserted range overlaps, or is adjacent to, ranges at positions
    // [start_pos..end_pos[. Ranges before start_pos or at or after end_pos are
    // not affected by the insertion.
    // If start_pos == end_pos, the range must be inserted before start_pos.
    // if start_pos < end_pos, the entire range from start_pos to end_pos
    // must be merged with the insert range.
  
    if (start_pos == end_pos) {
      // Insert between existing ranges at position start_pos.
      if (start_pos < count) {
        MoveRanges(list, start_pos, start_pos + 1, count - start_pos);
      }
      list->at(start_pos) = insert;
      return count + 1;
    }
    if (start_pos + 1 == end_pos) {
      // Replace single existing range at position start_pos.
      CharacterRange to_replace = list->at(start_pos);
      int new_from = Min(to_replace.from(), from);
      int new_to = Max(to_replace.to(), to);
      list->at(start_pos) = CharacterRange(new_from, new_to);
      return count;
    }
    // Replace a number of existing ranges from start_pos to end_pos - 1.
    // Move the remaining ranges down.
  
    int new_from = Min(list->at(start_pos).from(), from);
    int new_to = Max(list->at(end_pos - 1).to(), to);
    if (end_pos < count) {
      MoveRanges(list, end_pos, start_pos + 1, count - end_pos);
    }
    list->at(start_pos) = CharacterRange(new_from, new_to);
    return count - (end_pos - start_pos) + 1;
  }
  
  
  void CharacterSet::Canonicalize() {
    // Special/default classes are always considered canonical. The result
    // of calling ranges() will be sorted.
    if (ranges_ == NULL) return;
    CharacterRange::Canonicalize(ranges_);
  }
  
  
  void CharacterRange::Canonicalize(ZoneList<CharacterRange>* character_ranges) {
    if (character_ranges->length() <= 1) return;
    // Check whether ranges are already canonical (increasing, non-overlapping,
    // non-adjacent).
    int n = character_ranges->length();
    int max = character_ranges->at(0).to();
    int i = 1;
    while (i < n) {
      CharacterRange current = character_ranges->at(i);
      if (current.from() <= max + 1) {
        break;
      }
      max = current.to();
      i++;
    }
    // Canonical until the i'th range. If that's all of them, we are done.
    if (i == n) return;
  
    // The ranges at index i and forward are not canonicalized. Make them so by
    // doing the equivalent of insertion sort (inserting each into the previous
    // list, in order).
    // Notice that inserting a range can reduce the number of ranges in the
    // result due to combining of adjacent and overlapping ranges.
    int read = i;  // Range to insert.
    int num_canonical = i;  // Length of canonicalized part of list.
    do {
      num_canonical = InsertRangeInCanonicalList(character_ranges,
                                                 num_canonical,
                                                 character_ranges->at(read));
      read++;
    } while (read < n);
    character_ranges->Rewind(num_canonical);
  
    ASSERT(CharacterRange::IsCanonical(character_ranges));
  }
  
  
  // Utility function for CharacterRange::Merge. Adds a range at the end of
  // a canonicalized range list, if necessary merging the range with the last
  // range of the list.
  static void AddRangeToSet(ZoneList<CharacterRange>* set, CharacterRange range) {
    if (set == NULL) return;
    ASSERT(set->length() == 0 || set->at(set->length() - 1).to() < range.from());
    int n = set->length();
    if (n > 0) {
      CharacterRange lastRange = set->at(n - 1);
      if (lastRange.to() == range.from() - 1) {
        set->at(n - 1) = CharacterRange(lastRange.from(), range.to());
        return;
      }
    }
    set->Add(range);
  }
  
  
  static void AddRangeToSelectedSet(int selector,
                                    ZoneList<CharacterRange>* first_set,
                                    ZoneList<CharacterRange>* second_set,
                                    ZoneList<CharacterRange>* intersection_set,
                                    CharacterRange range) {
    switch (selector) {
      case kInsideFirst:
        AddRangeToSet(first_set, range);
        break;
      case kInsideSecond:
        AddRangeToSet(second_set, range);
        break;
      case kInsideBoth:
        AddRangeToSet(intersection_set, range);
        break;
    }
  }
  
  
  
  void CharacterRange::Merge(ZoneList<CharacterRange>* first_set,
                             ZoneList<CharacterRange>* second_set,
                             ZoneList<CharacterRange>* first_set_only_out,
                             ZoneList<CharacterRange>* second_set_only_out,
                             ZoneList<CharacterRange>* both_sets_out) {
    // Inputs are canonicalized.
    ASSERT(CharacterRange::IsCanonical(first_set));
    ASSERT(CharacterRange::IsCanonical(second_set));
    // Outputs are empty, if applicable.
    ASSERT(first_set_only_out == NULL || first_set_only_out->length() == 0);
    ASSERT(second_set_only_out == NULL || second_set_only_out->length() == 0);
    ASSERT(both_sets_out == NULL || both_sets_out->length() == 0);
  
    // Merge sets by iterating through the lists in order of lowest "from" value,
    // and putting intervals into one of three sets.
  
    if (first_set->length() == 0) {
      second_set_only_out->AddAll(*second_set);
      return;
    }
    if (second_set->length() == 0) {
      first_set_only_out->AddAll(*first_set);
      return;
    }
    // Indices into input lists.
    int i1 = 0;
    int i2 = 0;
    // Cache length of input lists.
    int n1 = first_set->length();
    int n2 = second_set->length();
    // Current range. May be invalid if state is kInsideNone.
    int from = 0;
    int to = -1;
    // Where current range comes from.
    int state = kInsideNone;
  
    while (i1 < n1 || i2 < n2) {
      CharacterRange next_range;
      int range_source;
      if (i2 == n2 ||
          (i1 < n1 && first_set->at(i1).from() < second_set->at(i2).from())) {
        // Next smallest element is in first set.
        next_range = first_set->at(i1++);
        range_source = kInsideFirst;
      } else {
        // Next smallest element is in second set.
        next_range = second_set->at(i2++);
        range_source = kInsideSecond;
      }
      if (to < next_range.from()) {
        // Ranges disjoint: |current|  |next|
        AddRangeToSelectedSet(state,
                              first_set_only_out,
                              second_set_only_out,
                              both_sets_out,
                              CharacterRange(from, to));
        from = next_range.from();
        to = next_range.to();
        state = range_source;
      } else {
        if (from < next_range.from()) {
          AddRangeToSelectedSet(state,
                                first_set_only_out,
                                second_set_only_out,
                                both_sets_out,
                                CharacterRange(from, next_range.from()-1));
        }
        if (to < next_range.to()) {
          // Ranges overlap:  |current|
          //                       |next|
          AddRangeToSelectedSet(state | range_source,
                                first_set_only_out,
                                second_set_only_out,
                                both_sets_out,
                                CharacterRange(next_range.from(), to));
          from = to + 1;
          to = next_range.to();
          state = range_source;
        } else {
          // Range included:    |current| , possibly ending at same character.
          //                      |next|
          AddRangeToSelectedSet(
              state | range_source,
              first_set_only_out,
              second_set_only_out,
              both_sets_out,
              CharacterRange(next_range.from(), next_range.to()));
          from = next_range.to() + 1;
          // If ranges end at same character, both ranges are consumed completely.
          if (next_range.to() == to) state = kInsideNone;
        }
      }
    }
    AddRangeToSelectedSet(state,
                          first_set_only_out,
                          second_set_only_out,
                          both_sets_out,
                          CharacterRange(from, to));
  }
  
  
  void CharacterRange::Negate(ZoneList<CharacterRange>* ranges,
                              ZoneList<CharacterRange>* negated_ranges) {
    ASSERT(CharacterRange::IsCanonical(ranges));
    ASSERT_EQ(0, negated_ranges->length());
    int range_count = ranges->length();
    uc16 from = 0;
    int i = 0;
    if (range_count > 0 && ranges->at(0).from() == 0) {
      from = ranges->at(0).to();
      i = 1;
    }
    while (i < range_count) {
      CharacterRange range = ranges->at(i);
      negated_ranges->Add(CharacterRange(from + 1, range.from() - 1));
      from = range.to();
      i++;
    }
    if (from < String::kMaxUC16CharCode) {
      negated_ranges->Add(CharacterRange(from + 1, String::kMaxUC16CharCode));
    }
  }
  
  
  
  // -------------------------------------------------------------------
  // Interest propagation
  
  
  RegExpNode* RegExpNode::TryGetSibling(NodeInfo* info) {
    for (int i = 0; i < siblings_.length(); i++) {
      RegExpNode* sibling = siblings_.Get(i);
      if (sibling->info()->Matches(info))
        return sibling;
    }
    return NULL;
  }
  
  
  RegExpNode* RegExpNode::EnsureSibling(NodeInfo* info, bool* cloned) {
    ASSERT_EQ(false, *cloned);
    siblings_.Ensure(this);
    RegExpNode* result = TryGetSibling(info);
    if (result != NULL) return result;
    result = this->Clone();
    NodeInfo* new_info = result->info();
    new_info->ResetCompilationState();
    new_info->AddFromPreceding(info);
    AddSibling(result);
    *cloned = true;
    return result;
  }
  
  
  template <class C>
  static RegExpNode* PropagateToEndpoint(C* node, NodeInfo* info) {
    NodeInfo full_info(*node->info());
    full_info.AddFromPreceding(info);
    bool cloned = false;
    return RegExpNode::EnsureSibling(node, &full_info, &cloned);
  }
  
  
  // -------------------------------------------------------------------
  // Splay tree
  
  
  OutSet* OutSet::Extend(unsigned value) {
    if (Get(value))
      return this;
    if (successors() != NULL) {
      for (int i = 0; i < successors()->length(); i++) {
        OutSet* successor = successors()->at(i);
        if (successor->Get(value))
          return successor;
      }
    } else {
      successors_ = new ZoneList<OutSet*>(2);
    }
    OutSet* result = new OutSet(first_, remaining_);
    result->Set(value);
    successors()->Add(result);
    return result;
  }
  
  
  void OutSet::Set(unsigned value) {
    if (value < kFirstLimit) {
      first_ |= (1 << value);
    } else {
      if (remaining_ == NULL)
        remaining_ = new ZoneList<unsigned>(1);
      if (remaining_->is_empty() || !remaining_->Contains(value))
        remaining_->Add(value);
    }
  }
  
  
  bool OutSet::Get(unsigned value) {
    if (value < kFirstLimit) {
      return (first_ & (1 << value)) != 0;
    } else if (remaining_ == NULL) {
      return false;
    } else {
      return remaining_->Contains(value);
    }
  }
  
  
  const uc16 DispatchTable::Config::kNoKey = unibrow::Utf8::kBadChar;
  
  
  void DispatchTable::AddRange(CharacterRange full_range, int value) {
    CharacterRange current = full_range;
    if (tree()->is_empty()) {
      // If this is the first range we just insert into the table.
      ZoneSplayTree<Config>::Locator loc;
      ASSERT_RESULT(tree()->Insert(current.from(), &loc));
      loc.set_value(Entry(current.from(), current.to(), empty()->Extend(value)));
      return;
    }
    // First see if there is a range to the left of this one that
    // overlaps.
    ZoneSplayTree<Config>::Locator loc;
    if (tree()->FindGreatestLessThan(current.from(), &loc)) {
      Entry* entry = &loc.value();
      // If we've found a range that overlaps with this one, and it
      // starts strictly to the left of this one, we have to fix it
      // because the following code only handles ranges that start on
      // or after the start point of the range we're adding.
      if (entry->from() < current.from() && entry->to() >= current.from()) {
        // Snap the overlapping range in half around the start point of
        // the range we're adding.
        CharacterRange left(entry->from(), current.from() - 1);
        CharacterRange right(current.from(), entry->to());
        // The left part of the overlapping range doesn't overlap.
        // Truncate the whole entry to be just the left part.
        entry->set_to(left.to());
        // The right part is the one that overlaps.  We add this part
        // to the map and let the next step deal with merging it with
        // the range we're adding.
        ZoneSplayTree<Config>::Locator loc;
        ASSERT_RESULT(tree()->Insert(right.from(), &loc));
        loc.set_value(Entry(right.from(),
                            right.to(),
                            entry->out_set()));
      }
    }
    while (current.is_valid()) {
      if (tree()->FindLeastGreaterThan(current.from(), &loc) &&
          (loc.value().from() <= current.to()) &&
          (loc.value().to() >= current.from())) {
        Entry* entry = &loc.value();
        // We have overlap.  If there is space between the start point of
        // the range we're adding and where the overlapping range starts
        // then we have to add a range covering just that space.
        if (current.from() < entry->from()) {
          ZoneSplayTree<Config>::Locator ins;
          ASSERT_RESULT(tree()->Insert(current.from(), &ins));
          ins.set_value(Entry(current.from(),
                              entry->from() - 1,
                              empty()->Extend(value)));
          current.set_from(entry->from());
        }
        ASSERT_EQ(current.from(), entry->from());
        // If the overlapping range extends beyond the one we want to add
        // we have to snap the right part off and add it separately.
        if (entry->to() > current.to()) {
          ZoneSplayTree<Config>::Locator ins;
          ASSERT_RESULT(tree()->Insert(current.to() + 1, &ins));
          ins.set_value(Entry(current.to() + 1,
                              entry->to(),
                              entry->out_set()));
          entry->set_to(current.to());
        }
        ASSERT(entry->to() <= current.to());
        // The overlapping range is now completely contained by the range
        // we're adding so we can just update it and move the start point
        // of the range we're adding just past it.
        entry->AddValue(value);
        // Bail out if the last interval ended at 0xFFFF since otherwise
        // adding 1 will wrap around to 0.
        if (entry->to() == String::kMaxUC16CharCode)
          break;
        ASSERT(entry->to() + 1 > current.from());
        current.set_from(entry->to() + 1);
      } else {
        // There is no overlap so we can just add the range
        ZoneSplayTree<Config>::Locator ins;
        ASSERT_RESULT(tree()->Insert(current.from(), &ins));
        ins.set_value(Entry(current.from(),
                            current.to(),
                            empty()->Extend(value)));
        break;
      }
    }
  }
  
  
  OutSet* DispatchTable::Get(uc16 value) {
    ZoneSplayTree<Config>::Locator loc;
    if (!tree()->FindGreatestLessThan(value, &loc))
      return empty();
    Entry* entry = &loc.value();
    if (value <= entry->to())
      return entry->out_set();
    else
      return empty();
  }
  
  
  // -------------------------------------------------------------------
  // Analysis
  
  
  void Analysis::EnsureAnalyzed(RegExpNode* that) {
    StackLimitCheck check(Isolate::Current());
    if (check.HasOverflowed()) {
      fail("Stack overflow");
      return;
    }
    if (that->info()->been_analyzed || that->info()->being_analyzed)
      return;
    that->info()->being_analyzed = true;
    that->Accept(this);
    that->info()->being_analyzed = false;
    that->info()->been_analyzed = true;
  }
  
  
  void Analysis::VisitEnd(EndNode* that) {
    // nothing to do
  }
  
  
  void TextNode::CalculateOffsets() {
    int element_count = elements()->length();
    // Set up the offsets of the elements relative to the start.  This is a fixed
    // quantity since a TextNode can only contain fixed-width things.
    int cp_offset = 0;
    for (int i = 0; i < element_count; i++) {
      TextElement& elm = elements()->at(i);
      elm.cp_offset = cp_offset;
      if (elm.type == TextElement::ATOM) {
        cp_offset += elm.data.u_atom->data().length();
      } else {
        cp_offset++;
      }
    }
  }
  
  
  void Analysis::VisitText(TextNode* that) {
    if (ignore_case_) {
      that->MakeCaseIndependent(is_ascii_);
    }
    EnsureAnalyzed(that->on_success());
    if (!has_failed()) {
      that->CalculateOffsets();
    }
  }
  
  
  void Analysis::VisitAction(ActionNode* that) {
    RegExpNode* target = that->on_success();
    EnsureAnalyzed(target);
    if (!has_failed()) {
      // If the next node is interested in what it follows then this node
      // has to be interested too so it can pass the information on.
      that->info()->AddFromFollowing(target->info());
    }
  }
  
  
  void Analysis::VisitChoice(ChoiceNode* that) {
    NodeInfo* info = that->info();
    for (int i = 0; i < that->alternatives()->length(); i++) {
      RegExpNode* node = that->alternatives()->at(i).node();
      EnsureAnalyzed(node);
      if (has_failed()) return;
      // Anything the following nodes need to know has to be known by
      // this node also, so it can pass it on.
      info->AddFromFollowing(node->info());
    }
  }
  
  
  void Analysis::VisitLoopChoice(LoopChoiceNode* that) {
    NodeInfo* info = that->info();
    for (int i = 0; i < that->alternatives()->length(); i++) {
      RegExpNode* node = that->alternatives()->at(i).node();
      if (node != that->loop_node()) {
        EnsureAnalyzed(node);
        if (has_failed()) return;
        info->AddFromFollowing(node->info());
      }
    }
    // Check the loop last since it may need the value of this node
    // to get a correct result.
    EnsureAnalyzed(that->loop_node());
    if (!has_failed()) {
      info->AddFromFollowing(that->loop_node()->info());
    }
  }
  
  
  void Analysis::VisitBackReference(BackReferenceNode* that) {
    EnsureAnalyzed(that->on_success());
  }
  
  
  void Analysis::VisitAssertion(AssertionNode* that) {
    EnsureAnalyzed(that->on_success());
    AssertionNode::AssertionNodeType type = that->type();
    if (type == AssertionNode::AT_BOUNDARY ||
        type == AssertionNode::AT_NON_BOUNDARY) {
      // Check if the following character is known to be a word character
      // or known to not be a word character.
      ZoneList<CharacterRange>* following_chars = that->FirstCharacterSet();
  
      CharacterRange::Canonicalize(following_chars);
  
      SetRelation word_relation =
          CharacterRange::WordCharacterRelation(following_chars);
      if (word_relation.Disjoint()) {
        // Includes the case where following_chars is empty (e.g., end-of-input).
        // Following character is definitely *not* a word character.
        type = (type == AssertionNode::AT_BOUNDARY) ?
                   AssertionNode::AFTER_WORD_CHARACTER :
                   AssertionNode::AFTER_NONWORD_CHARACTER;
        that->set_type(type);
      } else if (word_relation.ContainedIn()) {
        // Following character is definitely a word character.
        type = (type == AssertionNode::AT_BOUNDARY) ?
                   AssertionNode::AFTER_NONWORD_CHARACTER :
                   AssertionNode::AFTER_WORD_CHARACTER;
        that->set_type(type);
      }
    }
  }
  
  
  ZoneList<CharacterRange>* RegExpNode::FirstCharacterSet() {
    if (first_character_set_ == NULL) {
      if (ComputeFirstCharacterSet(kFirstCharBudget) < 0) {
        // If we can't find an exact solution within the budget, we
        // set the value to the set of every character, i.e., all characters
        // are possible.
        ZoneList<CharacterRange>* all_set = new ZoneList<CharacterRange>(1);
        all_set->Add(CharacterRange::Everything());
        first_character_set_ = all_set;
      }
    }
    return first_character_set_;
  }
  
  
  int RegExpNode::ComputeFirstCharacterSet(int budget) {
    // Default behavior is to not be able to determine the first character.
    return kComputeFirstCharacterSetFail;
  }
  
  
  int LoopChoiceNode::ComputeFirstCharacterSet(int budget) {
    budget--;
    if (budget >= 0) {
      // Find loop min-iteration. It's the value of the guarded choice node
      // with a GEQ guard, if any.
      int min_repetition = 0;
  
      for (int i = 0; i <= 1; i++) {
        GuardedAlternative alternative = alternatives()->at(i);
        ZoneList<Guard*>* guards = alternative.guards();
        if (guards != NULL && guards->length() > 0) {
          Guard* guard = guards->at(0);
          if (guard->op() == Guard::GEQ) {
            min_repetition = guard->value();
            break;
          }
        }
      }
  
      budget = loop_node()->ComputeFirstCharacterSet(budget);
      if (budget >= 0) {
        ZoneList<CharacterRange>* character_set =
            loop_node()->first_character_set();
        if (body_can_be_zero_length() || min_repetition == 0) {
          budget = continue_node()->ComputeFirstCharacterSet(budget);
          if (budget < 0) return budget;
          ZoneList<CharacterRange>* body_set =
              continue_node()->first_character_set();
          ZoneList<CharacterRange>* union_set =
            new ZoneList<CharacterRange>(Max(character_set->length(),
                                             body_set->length()));
          CharacterRange::Merge(character_set,
                                body_set,
                                union_set,
                                union_set,
                                union_set);
          character_set = union_set;
        }
        set_first_character_set(character_set);
      }
    }
    return budget;
  }
  
  
  int NegativeLookaheadChoiceNode::ComputeFirstCharacterSet(int budget) {
    budget--;
    if (budget >= 0) {
      GuardedAlternative successor = this->alternatives()->at(1);
      RegExpNode* successor_node = successor.node();
      budget = successor_node->ComputeFirstCharacterSet(budget);
      if (budget >= 0) {
        set_first_character_set(successor_node->first_character_set());
      }
    }
    return budget;
  }
  
  
  // The first character set of an EndNode is unknowable. Just use the
  // default implementation that fails and returns all characters as possible.
  
  
  int AssertionNode::ComputeFirstCharacterSet(int budget) {
    budget -= 1;
    if (budget >= 0) {
      switch (type_) {
        case AT_END: {
          set_first_character_set(new ZoneList<CharacterRange>(0));
          break;
        }
        case AT_START:
        case AT_BOUNDARY:
        case AT_NON_BOUNDARY:
        case AFTER_NEWLINE:
        case AFTER_NONWORD_CHARACTER:
        case AFTER_WORD_CHARACTER: {
          ASSERT_NOT_NULL(on_success());
          budget = on_success()->ComputeFirstCharacterSet(budget);
          if (budget >= 0) {
            set_first_character_set(on_success()->first_character_set());
          }
          break;
        }
      }
    }
    return budget;
  }
  
  
  int ActionNode::ComputeFirstCharacterSet(int budget) {
    if (type_ == POSITIVE_SUBMATCH_SUCCESS) return kComputeFirstCharacterSetFail;
    budget--;
    if (budget >= 0) {
      ASSERT_NOT_NULL(on_success());
      budget = on_success()->ComputeFirstCharacterSet(budget);
      if (budget >= 0) {
        set_first_character_set(on_success()->first_character_set());
      }
    }
    return budget;
  }
  
  
  int BackReferenceNode::ComputeFirstCharacterSet(int budget) {
    // We don't know anything about the first character of a backreference
    // at this point.
    // The potential first characters are the first characters of the capture,
    // and the first characters of the on_success node, depending on whether the
    // capture can be empty and whether it is known to be participating or known
    // not to be.
    return kComputeFirstCharacterSetFail;
  }
  
  
  int TextNode::ComputeFirstCharacterSet(int budget) {
    budget--;
    if (budget >= 0) {
      ASSERT_NE(0, elements()->length());
      TextElement text = elements()->at(0);
      if (text.type == TextElement::ATOM) {
        RegExpAtom* atom = text.data.u_atom;
        ASSERT_NE(0, atom->length());
        uc16 first_char = atom->data()[0];
        ZoneList<CharacterRange>* range = new ZoneList<CharacterRange>(1);
        range->Add(CharacterRange(first_char, first_char));
        set_first_character_set(range);
      } else {
        ASSERT(text.type == TextElement::CHAR_CLASS);
        RegExpCharacterClass* char_class = text.data.u_char_class;
        ZoneList<CharacterRange>* ranges = char_class->ranges();
        // TODO(lrn): Canonicalize ranges when they are created
        // instead of waiting until now.
        CharacterRange::Canonicalize(ranges);
        if (char_class->is_negated()) {
          int length = ranges->length();
          int new_length = length + 1;
          if (length > 0) {
            if (ranges->at(0).from() == 0) new_length--;
            if (ranges->at(length - 1).to() == String::kMaxUC16CharCode) {
              new_length--;
            }
          }
          ZoneList<CharacterRange>* negated_ranges =
              new ZoneList<CharacterRange>(new_length);
          CharacterRange::Negate(ranges, negated_ranges);
          set_first_character_set(negated_ranges);
        } else {
          set_first_character_set(ranges);
        }
      }
    }
    return budget;
  }
  
  
  
  // -------------------------------------------------------------------
  // Dispatch table construction
  
  
  void DispatchTableConstructor::VisitEnd(EndNode* that) {
    AddRange(CharacterRange::Everything());
  }
  
  
  void DispatchTableConstructor::BuildTable(ChoiceNode* node) {
    node->set_being_calculated(true);
    ZoneList<GuardedAlternative>* alternatives = node->alternatives();
    for (int i = 0; i < alternatives->length(); i++) {
      set_choice_index(i);
      alternatives->at(i).node()->Accept(this);
    }
    node->set_being_calculated(false);
  }
  
  
  class AddDispatchRange {
   public:
    explicit AddDispatchRange(DispatchTableConstructor* constructor)
      : constructor_(constructor) { }
    void Call(uc32 from, DispatchTable::Entry entry);
   private:
    DispatchTableConstructor* constructor_;
  };
  
  
  void AddDispatchRange::Call(uc32 from, DispatchTable::Entry entry) {
    CharacterRange range(from, entry.to());
    constructor_->AddRange(range);
  }
  
  
  void DispatchTableConstructor::VisitChoice(ChoiceNode* node) {
    if (node->being_calculated())
      return;
    DispatchTable* table = node->GetTable(ignore_case_);
    AddDispatchRange adder(this);
    table->ForEach(&adder);
  }
  
  
  void DispatchTableConstructor::VisitBackReference(BackReferenceNode* that) {
    // TODO(160): Find the node that we refer back to and propagate its start
    // set back to here.  For now we just accept anything.
    AddRange(CharacterRange::Everything());
  }
  
  
  void DispatchTableConstructor::VisitAssertion(AssertionNode* that) {
    RegExpNode* target = that->on_success();
    target->Accept(this);
  }
  
  
  static int CompareRangeByFrom(const CharacterRange* a,
                                const CharacterRange* b) {
    return Compare<uc16>(a->from(), b->from());
  }
  
  
  void DispatchTableConstructor::AddInverse(ZoneList<CharacterRange>* ranges) {
    ranges->Sort(CompareRangeByFrom);
    uc16 last = 0;
    for (int i = 0; i < ranges->length(); i++) {
      CharacterRange range = ranges->at(i);
      if (last < range.from())
        AddRange(CharacterRange(last, range.from() - 1));
      if (range.to() >= last) {
        if (range.to() == String::kMaxUC16CharCode) {
          return;
        } else {
          last = range.to() + 1;
        }
      }
    }
    AddRange(CharacterRange(last, String::kMaxUC16CharCode));
  }
  
  
  void DispatchTableConstructor::VisitText(TextNode* that) {
    TextElement elm = that->elements()->at(0);
    switch (elm.type) {
      case TextElement::ATOM: {
        uc16 c = elm.data.u_atom->data()[0];
        AddRange(CharacterRange(c, c));
        break;
      }
      case TextElement::CHAR_CLASS: {
        RegExpCharacterClass* tree = elm.data.u_char_class;
        ZoneList<CharacterRange>* ranges = tree->ranges();
        if (tree->is_negated()) {
          AddInverse(ranges);
        } else {
          for (int i = 0; i < ranges->length(); i++)
            AddRange(ranges->at(i));
        }
        break;
      }
      default: {
        UNIMPLEMENTED();
      }
    }
  }
  
  
  void DispatchTableConstructor::VisitAction(ActionNode* that) {
    RegExpNode* target = that->on_success();
    target->Accept(this);
  }
  
  
  RegExpEngine::CompilationResult RegExpEngine::Compile(RegExpCompileData* data,
                                                        bool ignore_case,
                                                        bool is_multiline,
                                                        Handle<String> pattern,
                                                        bool is_ascii) {
    if ((data->capture_count + 1) * 2 - 1 > RegExpMacroAssembler::kMaxRegister) {
      return IrregexpRegExpTooBig();
    }
    RegExpCompiler compiler(data->capture_count, ignore_case, is_ascii);
    // Wrap the body of the regexp in capture #0.
    RegExpNode* captured_body = RegExpCapture::ToNode(data->tree,
                                                      0,
                                                      &compiler,
                                                      compiler.accept());
    RegExpNode* node = captured_body;
    bool is_end_anchored = data->tree->IsAnchoredAtEnd();
    bool is_start_anchored = data->tree->IsAnchoredAtStart();
    int max_length = data->tree->max_match();
    if (!is_start_anchored) {
      // Add a .*? at the beginning, outside the body capture, unless
      // this expression is anchored at the beginning.
      RegExpNode* loop_node =
          RegExpQuantifier::ToNode(0,
                                   RegExpTree::kInfinity,
                                   false,
                                   new RegExpCharacterClass('*'),
                                   &compiler,
                                   captured_body,
                                   data->contains_anchor);
  
      if (data->contains_anchor) {
        // Unroll loop once, to take care of the case that might start
        // at the start of input.
        ChoiceNode* first_step_node = new ChoiceNode(2);
        first_step_node->AddAlternative(GuardedAlternative(captured_body));
        first_step_node->AddAlternative(GuardedAlternative(
            new TextNode(new RegExpCharacterClass('*'), loop_node)));
        node = first_step_node;
      } else {
        node = loop_node;
      }
    }
    data->node = node;
    Analysis analysis(ignore_case, is_ascii);
    analysis.EnsureAnalyzed(node);
    if (analysis.has_failed()) {
      const char* error_message = analysis.error_message();
      return CompilationResult(error_message);
    }
  
    // Create the correct assembler for the architecture.
  #ifndef V8_INTERPRETED_REGEXP
    // Native regexp implementation.
  
    NativeRegExpMacroAssembler::Mode mode =
        is_ascii ? NativeRegExpMacroAssembler::ASCII
                 : NativeRegExpMacroAssembler::UC16;
  
  #if V8_TARGET_ARCH_IA32
    RegExpMacroAssemblerIA32 macro_assembler(mode, (data->capture_count + 1) * 2);
  #elif V8_TARGET_ARCH_X64
    RegExpMacroAssemblerX64 macro_assembler(mode, (data->capture_count + 1) * 2);
  #elif V8_TARGET_ARCH_ARM
    RegExpMacroAssemblerARM macro_assembler(mode, (data->capture_count + 1) * 2);
  #elif V8_TARGET_ARCH_MIPS
    RegExpMacroAssemblerMIPS macro_assembler(mode, (data->capture_count + 1) * 2);
  #endif
  
  #else  // V8_INTERPRETED_REGEXP
    // Interpreted regexp implementation.
    EmbeddedVector<byte, 1024> codes;
    RegExpMacroAssemblerIrregexp macro_assembler(codes);
  #endif  // V8_INTERPRETED_REGEXP
  
    // Inserted here, instead of in Assembler, because it depends on information
    // in the AST that isn't replicated in the Node structure.
    static const int kMaxBacksearchLimit = 1024;
    if (is_end_anchored &&
        !is_start_anchored &&
        max_length < kMaxBacksearchLimit) {
      macro_assembler.SetCurrentPositionFromEnd(max_length);
    }
  
    return compiler.Assemble(&macro_assembler,
                             node,
                             data->capture_count,
                             pattern);
  }
  
  
  }}  // namespace v8::internal
  