text: // Copyright 2012 the V8 project authors. All rights reserved.
  // Use of this source code is governed by a BSD-style license that can be
  // found in the LICENSE file.
  
  #if V8_TARGET_ARCH_MIPS
  
  #include "src/regexp/mips/regexp-macro-assembler-mips.h"
  
  #include "src/assembler-inl.h"
  #include "src/log.h"
  #include "src/macro-assembler.h"
  #include "src/objects-inl.h"
  #include "src/regexp/regexp-macro-assembler.h"
  #include "src/regexp/regexp-stack.h"
  #include "src/snapshot/embedded-data.h"
  #include "src/unicode.h"
  
  namespace v8 {
  namespace internal {
  
  #ifndef V8_INTERPRETED_REGEXP
  /*
   * This assembler uses the following register assignment convention
   * - t7 : Temporarily stores the index of capture start after a matching pass
   *        for a global regexp.
   * - t1 : Pointer to current Code object including heap object tag.
   * - t2 : Current position in input, as negative offset from end of string.
   *        Please notice that this is the byte offset, not the character offset!
   * - t3 : Currently loaded character. Must be loaded using
   *        LoadCurrentCharacter before using any of the dispatch methods.
   * - t4 : Points to tip of backtrack stack
   * - t5 : Unused.
   * - t6 : End of input (points to byte after last character in input).
   * - fp : Frame pointer. Used to access arguments, local variables and
   *         RegExp registers.
   * - sp : Points to tip of C stack.
   *
   * The remaining registers are free for computations.
   * Each call to a public method should retain this convention.
   *
   * The stack will have the following structure:
   *
   *  - fp[60]  Isolate* isolate   (address of the current isolate)
   *  - fp[56]  direct_call  (if 1, direct call from JavaScript code,
   *                          if 0, call through the runtime system).
   *  - fp[52]  stack_area_base (High end of the memory area to use as
   *                             backtracking stack).
   *  - fp[48]  capture array size (may fit multiple sets of matches)
   *  - fp[44]  int* capture_array (int[num_saved_registers_], for output).
   *  --- sp when called ---
   *  - fp[40]  return address      (lr).
   *  - fp[36]  old frame pointer   (r11).
   *  - fp[0..32]  backup of registers s0..s7.
   *  --- frame pointer ----
   *  - fp[-4]  end of input       (address of end of string).
   *  - fp[-8]  start of input     (address of first character in string).
   *  - fp[-12] start index        (character index of start).
   *  - fp[-16] void* input_string (location of a handle containing the string).
   *  - fp[-20] success counter    (only for global regexps to count matches).
   *  - fp[-24] Offset of location before start of input (effectively character
   *            position -1). Used to initialize capture registers to a
   *            non-position.
   *  - fp[-28] At start (if 1, we are starting at the start of the
   *    string, otherwise 0)
   *  - fp[-32] register 0         (Only positions must be stored in the first
   *  -         register 1          num_saved_registers_ registers)
   *  -         ...
   *  -         register num_registers-1
   *  --- sp ---
   *
   * The first num_saved_registers_ registers are initialized to point to
   * "character -1" in the string (i.e., char_size() bytes before the first
   * character of the string). The remaining registers start out as garbage.
   *
   * The data up to the return address must be placed there by the calling
   * code and the remaining arguments are passed in registers, e.g. by calling the
   * code entry as cast to a function with the signature:
   * int (*match)(String input_string,
   *              int start_index,
   *              Address start,
   *              Address end,
   *              int* capture_output_array,
   *              int num_capture_registers,
   *              byte* stack_area_base,
   *              bool direct_call = false,
   *              Isolate* isolate);
   * The call is performed by NativeRegExpMacroAssembler::Execute()
   * (in regexp-macro-assembler.cc) via the GeneratedCode wrapper.
   */
  
  #define __ ACCESS_MASM(masm_)
  
  RegExpMacroAssemblerMIPS::RegExpMacroAssemblerMIPS(Isolate* isolate, Zone* zone,
                                                     Mode mode,
                                                     int registers_to_save)
      : NativeRegExpMacroAssembler(isolate, zone),
        masm_(new MacroAssembler(isolate, nullptr, kRegExpCodeSize,
                                 CodeObjectRequired::kYes)),
        mode_(mode),
        num_registers_(registers_to_save),
        num_saved_registers_(registers_to_save),
        entry_label_(),
        start_label_(),
        success_label_(),
        backtrack_label_(),
        exit_label_(),
        internal_failure_label_() {
    DCHECK_EQ(0, registers_to_save % 2);
    __ jmp(&entry_label_);   // We'll write the entry code later.
    // If the code gets too big or corrupted, an internal exception will be
    // raised, and we will exit right away.
    __ bind(&internal_failure_label_);
    __ li(v0, Operand(FAILURE));
    __ Ret();
    __ bind(&start_label_);  // And then continue from here.
  }
  
  
  RegExpMacroAssemblerMIPS::~RegExpMacroAssemblerMIPS() {
    delete masm_;
    // Unuse labels in case we throw away the assembler without calling GetCode.
    entry_label_.Unuse();
    start_label_.Unuse();
    success_label_.Unuse();
    backtrack_label_.Unuse();
    exit_label_.Unuse();
    check_preempt_label_.Unuse();
    stack_overflow_label_.Unuse();
    internal_failure_label_.Unuse();
  }
  
  
  int RegExpMacroAssemblerMIPS::stack_limit_slack()  {
    return RegExpStack::kStackLimitSlack;
  }
  
  
  void RegExpMacroAssemblerMIPS::AdvanceCurrentPosition(int by) {
    if (by != 0) {
      __ Addu(current_input_offset(),
              current_input_offset(), Operand(by * char_size()));
    }
  }
  
  
  void RegExpMacroAssemblerMIPS::AdvanceRegister(int reg, int by) {
    DCHECK_LE(0, reg);
    DCHECK_GT(num_registers_, reg);
    if (by != 0) {
      __ lw(a0, register_location(reg));
      __ Addu(a0, a0, Operand(by));
      __ sw(a0, register_location(reg));
    }
  }
  
  
  void RegExpMacroAssemblerMIPS::Backtrack() {
    CheckPreemption();
    // Pop Code offset from backtrack stack, add Code and jump to location.
    Pop(a0);
    __ Addu(a0, a0, code_pointer());
    __ Jump(a0);
  }
  
  
  void RegExpMacroAssemblerMIPS::Bind(Label* label) {
    __ bind(label);
  }
  
  
  void RegExpMacroAssemblerMIPS::CheckCharacter(uint32_t c, Label* on_equal) {
    BranchOrBacktrack(on_equal, eq, current_character(), Operand(c));
  }
  
  
  void RegExpMacroAssemblerMIPS::CheckCharacterGT(uc16 limit, Label* on_greater) {
    BranchOrBacktrack(on_greater, gt, current_character(), Operand(limit));
  }
  
  
  void RegExpMacroAssemblerMIPS::CheckAtStart(Label* on_at_start) {
    __ lw(a1, MemOperand(frame_pointer(), kStringStartMinusOne));
    __ Addu(a0, current_input_offset(), Operand(-char_size()));
    BranchOrBacktrack(on_at_start, eq, a0, Operand(a1));
  }
  
  
  void RegExpMacroAssemblerMIPS::CheckNotAtStart(int cp_offset,
                                                 Label* on_not_at_start) {
    __ lw(a1, MemOperand(frame_pointer(), kStringStartMinusOne));
    __ Addu(a0, current_input_offset(),
            Operand(-char_size() + cp_offset * char_size()));
    BranchOrBacktrack(on_not_at_start, ne, a0, Operand(a1));
  }
  
  
  void RegExpMacroAssemblerMIPS::CheckCharacterLT(uc16 limit, Label* on_less) {
    BranchOrBacktrack(on_less, lt, current_character(), Operand(limit));
  }
  
  
  void RegExpMacroAssemblerMIPS::CheckGreedyLoop(Label* on_equal) {
    Label backtrack_non_equal;
    __ lw(a0, MemOperand(backtrack_stackpointer(), 0));
    __ Branch(&backtrack_non_equal, ne, current_input_offset(), Operand(a0));
    __ Addu(backtrack_stackpointer(),
            backtrack_stackpointer(),
            Operand(kPointerSize));
    __ bind(&backtrack_non_equal);
    BranchOrBacktrack(on_equal, eq, current_input_offset(), Operand(a0));
  }
  
  
  void RegExpMacroAssemblerMIPS::CheckNotBackReferenceIgnoreCase(
      int start_reg, bool read_backward, bool unicode, Label* on_no_match) {
    Label fallthrough;
    __ lw(a0, register_location(start_reg));  // Index of start of capture.
    __ lw(a1, register_location(start_reg + 1));  // Index of end of capture.
    __ Subu(a1, a1, a0);  // Length of capture.
  
    // At this point, the capture registers are either both set or both cleared.
    // If the capture length is zero, then the capture is either empty or cleared.
    // Fall through in both cases.
    __ Branch(&fallthrough, eq, a1, Operand(zero_reg));
  
    if (read_backward) {
      __ lw(t0, MemOperand(frame_pointer(), kStringStartMinusOne));
      __ Addu(t0, t0, a1);
      BranchOrBacktrack(on_no_match, le, current_input_offset(), Operand(t0));
    } else {
      __ Addu(t5, a1, current_input_offset());
      // Check that there are enough characters left in the input.
      BranchOrBacktrack(on_no_match, gt, t5, Operand(zero_reg));
    }
  
    if (mode_ == LATIN1) {
      Label success;
      Label fail;
      Label loop_check;
  
      // a0 - offset of start of capture.
      // a1 - length of capture.
      __ Addu(a0, a0, Operand(end_of_input_address()));
      __ Addu(a2, end_of_input_address(), Operand(current_input_offset()));
      if (read_backward) {
        __ Subu(a2, a2, Operand(a1));
      }
      __ Addu(a1, a0, Operand(a1));
  
      // a0 - Address of start of capture.
      // a1 - Address of end of capture.
      // a2 - Address of current input position.
  
      Label loop;
      __ bind(&loop);
      __ lbu(a3, MemOperand(a0, 0));
      __ addiu(a0, a0, char_size());
      __ lbu(t0, MemOperand(a2, 0));
      __ addiu(a2, a2, char_size());
  
      __ Branch(&loop_check, eq, t0, Operand(a3));
  
      // Mismatch, try case-insensitive match (converting letters to lower-case).
      __ Or(a3, a3, Operand(0x20));  // Convert capture character to lower-case.
      __ Or(t0, t0, Operand(0x20));  // Also convert input character.
      __ Branch(&fail, ne, t0, Operand(a3));
      __ Subu(a3, a3, Operand('a'));
      __ Branch(&loop_check, ls, a3, Operand('z' - 'a'));
      // Latin-1: Check for values in range [224,254] but not 247.
      __ Subu(a3, a3, Operand(224 - 'a'));
      // Weren't Latin-1 letters.
      __ Branch(&fail, hi, a3, Operand(254 - 224));
      // Check for 247.
      __ Branch(&fail, eq, a3, Operand(247 - 224));
  
      __ bind(&loop_check);
      __ Branch(&loop, lt, a0, Operand(a1));
      __ jmp(&success);
  
      __ bind(&fail);
      GoTo(on_no_match);
  
      __ bind(&success);
      // Compute new value of character position after the matched part.
      __ Subu(current_input_offset(), a2, end_of_input_address());
      if (read_backward) {
        __ lw(t0, register_location(start_reg));  // Index of start of capture.
        __ lw(t5, register_location(start_reg + 1));  // Index of end of capture.
        __ Addu(current_input_offset(), current_input_offset(), Operand(t0));
        __ Subu(current_input_offset(), current_input_offset(), Operand(t5));
      }
    } else {
      DCHECK_EQ(UC16, mode_);
      // Put regexp engine registers on stack.
      RegList regexp_registers_to_retain = current_input_offset().bit() |
          current_character().bit() | backtrack_stackpointer().bit();
      __ MultiPush(regexp_registers_to_retain);
  
      int argument_count = 4;
      __ PrepareCallCFunction(argument_count, a2);
  
      // a0 - offset of start of capture.
      // a1 - length of capture.
  
      // Put arguments into arguments registers.
      // Parameters are
      //   a0: Address byte_offset1 - Address captured substring's start.
      //   a1: Address byte_offset2 - Address of current character position.
      //   a2: size_t byte_length - length of capture in bytes(!).
      //   a3: Isolate* isolate or 0 if unicode flag.
  
      // Address of start of capture.
      __ Addu(a0, a0, Operand(end_of_input_address()));
      // Length of capture.
      __ mov(a2, a1);
      // Save length in callee-save register for use on return.
      __ mov(s3, a1);
      // Address of current input position.
      __ Addu(a1, current_input_offset(), Operand(end_of_input_address()));
      if (read_backward) {
        __ Subu(a1, a1, Operand(s3));
      }
      // Isolate.
  #ifdef V8_INTL_SUPPORT
      if (unicode) {
        __ mov(a3, zero_reg);
      } else  // NOLINT
  #endif      // V8_INTL_SUPPORT
      {
        __ li(a3, Operand(ExternalReference::isolate_address(masm_->isolate())));
      }
  
      {
        AllowExternalCallThatCantCauseGC scope(masm_);
        ExternalReference function =
            ExternalReference::re_case_insensitive_compare_uc16(masm_->isolate());
        __ CallCFunction(function, argument_count);
      }
  
      // Restore regexp engine registers.
      __ MultiPop(regexp_registers_to_retain);
      __ li(code_pointer(), Operand(masm_->CodeObject()), CONSTANT_SIZE);
      __ lw(end_of_input_address(), MemOperand(frame_pointer(), kInputEnd));
  
      // Check if function returned non-zero for success or zero for failure.
      BranchOrBacktrack(on_no_match, eq, v0, Operand(zero_reg));
      // On success, advance position by length of capture.
      if (read_backward) {
        __ Subu(current_input_offset(), current_input_offset(), Operand(s3));
      } else {
        __ Addu(current_input_offset(), current_input_offset(), Operand(s3));
      }
    }
  
    __ bind(&fallthrough);
  }
  
  
  void RegExpMacroAssemblerMIPS::CheckNotBackReference(int start_reg,
                                                       bool read_backward,
                                                       Label* on_no_match) {
    Label fallthrough;
    Label success;
  
    // Find length of back-referenced capture.
    __ lw(a0, register_location(start_reg));
    __ lw(a1, register_location(start_reg + 1));
    __ Subu(a1, a1, a0);  // Length to check.
  
    // At this point, the capture registers are either both set or both cleared.
    // If the capture length is zero, then the capture is either empty or cleared.
    // Fall through in both cases.
    __ Branch(&fallthrough, le, a1, Operand(zero_reg));
  
    if (read_backward) {
      __ lw(t0, MemOperand(frame_pointer(), kStringStartMinusOne));
      __ Addu(t0, t0, a1);
      BranchOrBacktrack(on_no_match, le, current_input_offset(), Operand(t0));
    } else {
      __ Addu(t5, a1, current_input_offset());
      // Check that there are enough characters left in the input.
      BranchOrBacktrack(on_no_match, gt, t5, Operand(zero_reg));
    }
  
    // a0 - offset of start of capture.
    // a1 - length of capture.
    __ Addu(a0, a0, Operand(end_of_input_address()));
    __ Addu(a2, end_of_input_address(), Operand(current_input_offset()));
    if (read_backward) {
      __ Subu(a2, a2, Operand(a1));
    }
    __ Addu(a1, a0, Operand(a1));
  
    // a0 - Address of start of capture.
    // a1 - Address of end of capture.
    // a2 - Address of current input position.
  
  
    Label loop;
    __ bind(&loop);
    if (mode_ == LATIN1) {
      __ lbu(a3, MemOperand(a0, 0));
      __ addiu(a0, a0, char_size());
      __ lbu(t0, MemOperand(a2, 0));
      __ addiu(a2, a2, char_size());
    } else {
      DCHECK(mode_ == UC16);
      __ lhu(a3, MemOperand(a0, 0));
      __ addiu(a0, a0, char_size());
      __ lhu(t0, MemOperand(a2, 0));
      __ addiu(a2, a2, char_size());
    }
    BranchOrBacktrack(on_no_match, ne, a3, Operand(t0));
    __ Branch(&loop, lt, a0, Operand(a1));
  
    // Move current character position to position after match.
    __ Subu(current_input_offset(), a2, end_of_input_address());
    if (read_backward) {
      __ lw(t0, register_location(start_reg));      // Index of start of capture.
      __ lw(t5, register_location(start_reg + 1));  // Index of end of capture.
      __ Addu(current_input_offset(), current_input_offset(), Operand(t0));
      __ Subu(current_input_offset(), current_input_offset(), Operand(t5));
    }
    __ bind(&fallthrough);
  }
  
  
  void RegExpMacroAssemblerMIPS::CheckNotCharacter(uint32_t c,
                                                   Label* on_not_equal) {
    BranchOrBacktrack(on_not_equal, ne, current_character(), Operand(c));
  }
  
  
  void RegExpMacroAssemblerMIPS::CheckCharacterAfterAnd(uint32_t c,
                                                        uint32_t mask,
                                                        Label* on_equal) {
    __ And(a0, current_character(), Operand(mask));
    Operand rhs = (c == 0) ? Operand(zero_reg) : Operand(c);
    BranchOrBacktrack(on_equal, eq, a0, rhs);
  }
  
  
  void RegExpMacroAssemblerMIPS::CheckNotCharacterAfterAnd(uint32_t c,
                                                           uint32_t mask,
                                                           Label* on_not_equal) {
    __ And(a0, current_character(), Operand(mask));
    Operand rhs = (c == 0) ? Operand(zero_reg) : Operand(c);
    BranchOrBacktrack(on_not_equal, ne, a0, rhs);
  }
  
  
  void RegExpMacroAssemblerMIPS::CheckNotCharacterAfterMinusAnd(
      uc16 c,
      uc16 minus,
      uc16 mask,
      Label* on_not_equal) {
    DCHECK_GT(String::kMaxUtf16CodeUnit, minus);
    __ Subu(a0, current_character(), Operand(minus));
    __ And(a0, a0, Operand(mask));
    BranchOrBacktrack(on_not_equal, ne, a0, Operand(c));
  }
  
  
  void RegExpMacroAssemblerMIPS::CheckCharacterInRange(
      uc16 from,
      uc16 to,
      Label* on_in_range) {
    __ Subu(a0, current_character(), Operand(from));
    // Unsigned lower-or-same condition.
    BranchOrBacktrack(on_in_range, ls, a0, Operand(to - from));
  }
  
  
  void RegExpMacroAssemblerMIPS::CheckCharacterNotInRange(
      uc16 from,
      uc16 to,
      Label* on_not_in_range) {
    __ Subu(a0, current_character(), Operand(from));
    // Unsigned higher condition.
    BranchOrBacktrack(on_not_in_range, hi, a0, Operand(to - from));
  }
  
  
  void RegExpMacroAssemblerMIPS::CheckBitInTable(
      Handle<ByteArray> table,
      Label* on_bit_set) {
    __ li(a0, Operand(table));
    if (mode_ != LATIN1 || kTableMask != String::kMaxOneByteCharCode) {
      __ And(a1, current_character(), Operand(kTableSize - 1));
      __ Addu(a0, a0, a1);
    } else {
      __ Addu(a0, a0, current_character());
    }
  
    __ lbu(a0, FieldMemOperand(a0, ByteArray::kHeaderSize));
    BranchOrBacktrack(on_bit_set, ne, a0, Operand(zero_reg));
  }
  
  
  bool RegExpMacroAssemblerMIPS::CheckSpecialCharacterClass(uc16 type,
                                                            Label* on_no_match) {
    // Range checks (c in min..max) are generally implemented by an unsigned
    // (c - min) <= (max - min) check.
    switch (type) {
    case 's':
      // Match space-characters.
      if (mode_ == LATIN1) {
        // One byte space characters are '\t'..'\r', ' ' and \u00a0.
        Label success;
        __ Branch(&success, eq, current_character(), Operand(' '));
        // Check range 0x09..0x0D.
        __ Subu(a0, current_character(), Operand('\t'));
        __ Branch(&success, ls, a0, Operand('\r' - '\t'));
        // \u00a0 (NBSP).
        BranchOrBacktrack(on_no_match, ne, a0, Operand(0x00A0 - '\t'));
        __ bind(&success);
        return true;
      }
      return false;
    case 'S':
      // The emitted code for generic character classes is good enough.
      return false;
    case 'd':
      // Match Latin1 digits ('0'..'9').
      __ Subu(a0, current_character(), Operand('0'));
      BranchOrBacktrack(on_no_match, hi, a0, Operand('9' - '0'));
      return true;
    case 'D':
      // Match non Latin1-digits.
      __ Subu(a0, current_character(), Operand('0'));
      BranchOrBacktrack(on_no_match, ls, a0, Operand('9' - '0'));
      return true;
    case '.': {
      // Match non-newlines (not 0x0A('\n'), 0x0D('\r'), 0x2028 and 0x2029).
      __ Xor(a0, current_character(), Operand(0x01));
      // See if current character is '\n'^1 or '\r'^1, i.e., 0x0B or 0x0C.
      __ Subu(a0, a0, Operand(0x0B));
      BranchOrBacktrack(on_no_match, ls, a0, Operand(0x0C - 0x0B));
      if (mode_ == UC16) {
        // Compare original value to 0x2028 and 0x2029, using the already
        // computed (current_char ^ 0x01 - 0x0B). I.e., check for
        // 0x201D (0x2028 - 0x0B) or 0x201E.
        __ Subu(a0, a0, Operand(0x2028 - 0x0B));
        BranchOrBacktrack(on_no_match, ls, a0, Operand(1));
      }
      return true;
    }
    case 'n': {
      // Match newlines (0x0A('\n'), 0x0D('\r'), 0x2028 and 0x2029).
      __ Xor(a0, current_character(), Operand(0x01));
      // See if current character is '\n'^1 or '\r'^1, i.e., 0x0B or 0x0C.
      __ Subu(a0, a0, Operand(0x0B));
      if (mode_ == LATIN1) {
        BranchOrBacktrack(on_no_match, hi, a0, Operand(0x0C - 0x0B));
      } else {
        Label done;
        BranchOrBacktrack(&done, ls, a0, Operand(0x0C - 0x0B));
        // Compare original value to 0x2028 and 0x2029, using the already
        // computed (current_char ^ 0x01 - 0x0B). I.e., check for
        // 0x201D (0x2028 - 0x0B) or 0x201E.
        __ Subu(a0, a0, Operand(0x2028 - 0x0B));
        BranchOrBacktrack(on_no_match, hi, a0, Operand(1));
        __ bind(&done);
      }
      return true;
    }
    case 'w': {
      if (mode_ != LATIN1) {
        // Table is 256 entries, so all Latin1 characters can be tested.
        BranchOrBacktrack(on_no_match, hi, current_character(), Operand('z'));
      }
      ExternalReference map = ExternalReference::re_word_character_map(isolate());
      __ li(a0, Operand(map));
      __ Addu(a0, a0, current_character());
      __ lbu(a0, MemOperand(a0, 0));
      BranchOrBacktrack(on_no_match, eq, a0, Operand(zero_reg));
      return true;
    }
    case 'W': {
      Label done;
      if (mode_ != LATIN1) {
        // Table is 256 entries, so all Latin1 characters can be tested.
        __ Branch(&done, hi, current_character(), Operand('z'));
      }
      ExternalReference map = ExternalReference::re_word_character_map(isolate());
      __ li(a0, Operand(map));
      __ Addu(a0, a0, current_character());
      __ lbu(a0, MemOperand(a0, 0));
      BranchOrBacktrack(on_no_match, ne, a0, Operand(zero_reg));
      if (mode_ != LATIN1) {
        __ bind(&done);
      }
      return true;
    }
    case '*':
      // Match any character.
      return true;
    // No custom implementation (yet): s(UC16), S(UC16).
    default:
      return false;
    }
  }
  
  
  void RegExpMacroAssemblerMIPS::Fail() {
    __ li(v0, Operand(FAILURE));
    __ jmp(&exit_label_);
  }
  
  
  Handle<HeapObject> RegExpMacroAssemblerMIPS::GetCode(Handle<String> source) {
    Label return_v0;
    if (masm_->has_exception()) {
      // If the code gets corrupted due to long regular expressions and lack of
      // space on trampolines, an internal exception flag is set. If this case
      // is detected, we will jump into exit sequence right away.
      __ bind_to(&entry_label_, internal_failure_label_.pos());
    } else {
      // Finalize code - write the entry point code now we know how many
      // registers we need.
  
      // Entry code:
      __ bind(&entry_label_);
  
      // Tell the system that we have a stack frame.  Because the type is MANUAL,
      // no is generated.
      FrameScope scope(masm_, StackFrame::MANUAL);
  
      // Actually emit code to start a new stack frame.
      // Push arguments
      // Save callee-save registers.
      // Start new stack frame.
      // Store link register in existing stack-cell.
      // Order here should correspond to order of offset constants in header file.
      RegList registers_to_retain = s0.bit() | s1.bit() | s2.bit() |
          s3.bit() | s4.bit() | s5.bit() | s6.bit() | s7.bit() | fp.bit();
      RegList argument_registers = a0.bit() | a1.bit() | a2.bit() | a3.bit();
      __ MultiPush(argument_registers | registers_to_retain | ra.bit());
      // Set frame pointer in space for it if this is not a direct call
      // from generated code.
      __ Addu(frame_pointer(), sp, Operand(4 * kPointerSize));
      __ mov(a0, zero_reg);
      __ push(a0);  // Make room for success counter and initialize it to 0.
      __ push(a0);  // Make room for "string start - 1" constant.
  
      // Check if we have space on the stack for registers.
      Label stack_limit_hit;
      Label stack_ok;
  
      ExternalReference stack_limit =
          ExternalReference::address_of_stack_limit(masm_->isolate());
      __ li(a0, Operand(stack_limit));
      __ lw(a0, MemOperand(a0));
      __ Subu(a0, sp, a0);
      // Handle it if the stack pointer is already below the stack limit.
      __ Branch(&stack_limit_hit, le, a0, Operand(zero_reg));
      // Check if there is room for the variable number of registers above
      // the stack limit.
      __ Branch(&stack_ok, hs, a0, Operand(num_registers_ * kPointerSize));
      // Exit with OutOfMemory exception. There is not enough space on the stack
      // for our working registers.
      __ li(v0, Operand(EXCEPTION));
      __ jmp(&return_v0);
  
      __ bind(&stack_limit_hit);
      CallCheckStackGuardState(a0);
      // If returned value is non-zero, we exit with the returned value as result.
      __ Branch(&return_v0, ne, v0, Operand(zero_reg));
  
      __ bind(&stack_ok);
      // Allocate space on stack for registers.
      __ Subu(sp, sp, Operand(num_registers_ * kPointerSize));
      // Load string end.
      __ lw(end_of_input_address(), MemOperand(frame_pointer(), kInputEnd));
      // Load input start.
      __ lw(a0, MemOperand(frame_pointer(), kInputStart));
      // Find negative length (offset of start relative to end).
      __ Subu(current_input_offset(), a0, end_of_input_address());
      // Set a0 to address of char before start of the input string
      // (effectively string position -1).
      __ lw(a1, MemOperand(frame_pointer(), kStartIndex));
      __ Subu(a0, current_input_offset(), Operand(char_size()));
      __ sll(t5, a1, (mode_ == UC16) ? 1 : 0);
      __ Subu(a0, a0, t5);
      // Store this value in a local variable, for use when clearing
      // position registers.
      __ sw(a0, MemOperand(frame_pointer(), kStringStartMinusOne));
  
      // Initialize code pointer register
      __ li(code_pointer(), Operand(masm_->CodeObject()), CONSTANT_SIZE);
  
      Label load_char_start_regexp, start_regexp;
      // Load newline if index is at start, previous character otherwise.
      __ Branch(&load_char_start_regexp, ne, a1, Operand(zero_reg));
      __ li(current_character(), Operand('\n'));
      __ jmp(&start_regexp);
  
      // Global regexp restarts matching here.
      __ bind(&load_char_start_regexp);
      // Load previous char as initial value of current character register.
      LoadCurrentCharacterUnchecked(-1, 1);
      __ bind(&start_regexp);
  
      // Initialize on-stack registers.
      if (num_saved_registers_ > 0) {  // Always is, if generated from a regexp.
        // Fill saved registers with initial value = start offset - 1.
        if (num_saved_registers_ > 8) {
          // Address of register 0.
          __ Addu(a1, frame_pointer(), Operand(kRegisterZero));
          __ li(a2, Operand(num_saved_registers_));
          Label init_loop;
          __ bind(&init_loop);
          __ sw(a0, MemOperand(a1));
          __ Addu(a1, a1, Operand(-kPointerSize));
          __ Subu(a2, a2, Operand(1));
          __ Branch(&init_loop, ne, a2, Operand(zero_reg));
        } else {
          for (int i = 0; i < num_saved_registers_; i++) {
            __ sw(a0, register_location(i));
          }
        }
      }
  
      // Initialize backtrack stack pointer.
      __ lw(backtrack_stackpointer(), MemOperand(frame_pointer(), kStackHighEnd));
  
      __ jmp(&start_label_);
  
  
      // Exit code:
      if (success_label_.is_linked()) {
        // Save captures when successful.
        __ bind(&success_label_);
        if (num_saved_registers_ > 0) {
          // Copy captures to output.
          __ lw(a1, MemOperand(frame_pointer(), kInputStart));
          __ lw(a0, MemOperand(frame_pointer(), kRegisterOutput));
          __ lw(a2, MemOperand(frame_pointer(), kStartIndex));
          __ Subu(a1, end_of_input_address(), a1);
          // a1 is length of input in bytes.
          if (mode_ == UC16) {
            __ srl(a1, a1, 1);
          }
          // a1 is length of input in characters.
          __ Addu(a1, a1, Operand(a2));
          // a1 is length of string in characters.
  
          DCHECK_EQ(0, num_saved_registers_ % 2);
          // Always an even number of capture registers. This allows us to
          // unroll the loop once to add an operation between a load of a register
          // and the following use of that register.
          for (int i = 0; i < num_saved_registers_; i += 2) {
            __ lw(a2, register_location(i));
            __ lw(a3, register_location(i + 1));
            if (i == 0 && global_with_zero_length_check()) {
              // Keep capture start in a4 for the zero-length check later.
              __ mov(t7, a2);
            }
            if (mode_ == UC16) {
              __ sra(a2, a2, 1);
              __ Addu(a2, a2, a1);
              __ sra(a3, a3, 1);
              __ Addu(a3, a3, a1);
            } else {
              __ Addu(a2, a1, Operand(a2));
              __ Addu(a3, a1, Operand(a3));
            }
            __ sw(a2, MemOperand(a0));
            __ Addu(a0, a0, kPointerSize);
            __ sw(a3, MemOperand(a0));
            __ Addu(a0, a0, kPointerSize);
          }
        }
  
        if (global()) {
          // Restart matching if the regular expression is flagged as global.
          __ lw(a0, MemOperand(frame_pointer(), kSuccessfulCaptures));
          __ lw(a1, MemOperand(frame_pointer(), kNumOutputRegisters));
          __ lw(a2, MemOperand(frame_pointer(), kRegisterOutput));
          // Increment success counter.
          __ Addu(a0, a0, 1);
          __ sw(a0, MemOperand(frame_pointer(), kSuccessfulCaptures));
          // Capture results have been stored, so the number of remaining global
          // output registers is reduced by the number of stored captures.
          __ Subu(a1, a1, num_saved_registers_);
          // Check whether we have enough room for another set of capture results.
          __ mov(v0, a0);
          __ Branch(&return_v0, lt, a1, Operand(num_saved_registers_));
  
          __ sw(a1, MemOperand(frame_pointer(), kNumOutputRegisters));
          // Advance the location for output.
          __ Addu(a2, a2, num_saved_registers_ * kPointerSize);
          __ sw(a2, MemOperand(frame_pointer(), kRegisterOutput));
  
          // Prepare a0 to initialize registers with its value in the next run.
          __ lw(a0, MemOperand(frame_pointer(), kStringStartMinusOne));
  
          if (global_with_zero_length_check()) {
            // Special case for zero-length matches.
            // t7: capture start index
            // Not a zero-length match, restart.
            __ Branch(
                &load_char_start_regexp, ne, current_input_offset(), Operand(t7));
            // Offset from the end is zero if we already reached the end.
            __ Branch(&exit_label_, eq, current_input_offset(),
                      Operand(zero_reg));
            // Advance current position after a zero-length match.
            Label advance;
            __ bind(&advance);
            __ Addu(current_input_offset(),
                    current_input_offset(),
                    Operand((mode_ == UC16) ? 2 : 1));
            if (global_unicode()) CheckNotInSurrogatePair(0, &advance);
          }
  
          __ Branch(&load_char_start_regexp);
        } else {
          __ li(v0, Operand(SUCCESS));
        }
      }
      // Exit and return v0.
      __ bind(&exit_label_);
      if (global()) {
        __ lw(v0, MemOperand(frame_pointer(), kSuccessfulCaptures));
      }
  
      __ bind(&return_v0);
      // Skip sp past regexp registers and local variables..
      __ mov(sp, frame_pointer());
      // Restore registers s0..s7 and return (restoring ra to pc).
      __ MultiPop(registers_to_retain | ra.bit());
      __ Ret();
  
      // Backtrack code (branch target for conditional backtracks).
      if (backtrack_label_.is_linked()) {
        __ bind(&backtrack_label_);
        Backtrack();
      }
  
      Label exit_with_exception;
  
      // Preempt-code.
      if (check_preempt_label_.is_linked()) {
        SafeCallTarget(&check_preempt_label_);
        // Put regexp engine registers on stack.
        RegList regexp_registers_to_retain = current_input_offset().bit() |
            current_character().bit() | backtrack_stackpointer().bit();
        __ MultiPush(regexp_registers_to_retain);
        CallCheckStackGuardState(a0);
        __ MultiPop(regexp_registers_to_retain);
        // If returning non-zero, we should end execution with the given
        // result as return value.
        __ Branch(&return_v0, ne, v0, Operand(zero_reg));
  
        // String might have moved: Reload end of string from frame.
        __ lw(end_of_input_address(), MemOperand(frame_pointer(), kInputEnd));
        __ li(code_pointer(), Operand(masm_->CodeObject()), CONSTANT_SIZE);
        SafeReturn();
      }
  
      // Backtrack stack overflow code.
      if (stack_overflow_label_.is_linked()) {
        SafeCallTarget(&stack_overflow_label_);
        // Reached if the backtrack-stack limit has been hit.
        // Put regexp engine registers on stack first.
        RegList regexp_registers = current_input_offset().bit() |
            current_character().bit();
        __ MultiPush(regexp_registers);
        Label grow_failed;
        // Call GrowStack(backtrack_stackpointer(), &stack_base)
        static const int num_arguments = 3;
        __ PrepareCallCFunction(num_arguments, a0);
        __ mov(a0, backtrack_stackpointer());
        __ Addu(a1, frame_pointer(), Operand(kStackHighEnd));
        __ li(a2, Operand(ExternalReference::isolate_address(masm_->isolate())));
        ExternalReference grow_stack =
            ExternalReference::re_grow_stack(masm_->isolate());
        __ CallCFunction(grow_stack, num_arguments);
        // Restore regexp registers.
        __ MultiPop(regexp_registers);
        // If return nullptr, we have failed to grow the stack, and
        // must exit with a stack-overflow exception.
        __ Branch(&exit_with_exception, eq, v0, Operand(zero_reg));
        // Otherwise use return value as new stack pointer.
        __ mov(backtrack_stackpointer(), v0);
        // Restore saved registers and continue.
        __ li(code_pointer(), Operand(masm_->CodeObject()), CONSTANT_SIZE);
        __ lw(end_of_input_address(), MemOperand(frame_pointer(), kInputEnd));
        SafeReturn();
      }
  
      if (exit_with_exception.is_linked()) {
        // If any of the code above needed to exit with an exception.
        __ bind(&exit_with_exception);
        // Exit with Result EXCEPTION(-1) to signal thrown exception.
        __ li(v0, Operand(EXCEPTION));
        __ jmp(&return_v0);
      }
    }
  
    CodeDesc code_desc;
    masm_->GetCode(isolate(), &code_desc);
    Handle<Code> code = isolate()->factory()->NewCode(code_desc, Code::REGEXP,
                                                      masm_->CodeObject());
    LOG(masm_->isolate(),
        RegExpCodeCreateEvent(AbstractCode::cast(*code), *source));
    return Handle<HeapObject>::cast(code);
  }
  
  
  void RegExpMacroAssemblerMIPS::GoTo(Label* to) {
    if (to == nullptr) {
      Backtrack();
      return;
    }
    __ jmp(to);
    return;
  }
  
  
  void RegExpMacroAssemblerMIPS::IfRegisterGE(int reg,
                                              int comparand,
                                              Label* if_ge) {
    __ lw(a0, register_location(reg));
      BranchOrBacktrack(if_ge, ge, a0, Operand(comparand));
  }
  
  
  void RegExpMacroAssemblerMIPS::IfRegisterLT(int reg,
                                              int comparand,
                                              Label* if_lt) {
    __ lw(a0, register_location(reg));
    BranchOrBacktrack(if_lt, lt, a0, Operand(comparand));
  }
  
  
  void RegExpMacroAssemblerMIPS::IfRegisterEqPos(int reg,
                                                 Label* if_eq) {
    __ lw(a0, register_location(reg));
    BranchOrBacktrack(if_eq, eq, a0, Operand(current_input_offset()));
  }
  
  
  RegExpMacroAssembler::IrregexpImplementation
      RegExpMacroAssemblerMIPS::Implementation() {
    return kMIPSImplementation;
  }
  
  
  void RegExpMacroAssemblerMIPS::LoadCurrentCharacter(int cp_offset,
                                                      Label* on_end_of_input,
                                                      bool check_bounds,
                                                      int characters) {
    DCHECK(cp_offset < (1<<30));  // Be sane! (And ensure negation works).
    if (check_bounds) {
      if (cp_offset >= 0) {
        CheckPosition(cp_offset + characters - 1, on_end_of_input);
      } else {
        CheckPosition(cp_offset, on_end_of_input);
      }
    }
    LoadCurrentCharacterUnchecked(cp_offset, characters);
  }
  
  
  void RegExpMacroAssemblerMIPS::PopCurrentPosition() {
    Pop(current_input_offset());
  }
  
  
  void RegExpMacroAssemblerMIPS::PopRegister(int register_index) {
    Pop(a0);
    __ sw(a0, register_location(register_index));
  }
  
  
  void RegExpMacroAssemblerMIPS::PushBacktrack(Label* label) {
    if (label->is_bound()) {
      int target = label->pos();
      __ li(a0, Operand(target + Code::kHeaderSize - kHeapObjectTag));
    } else {
      Assembler::BlockTrampolinePoolScope block_trampoline_pool(masm_);
      Label after_constant;
      __ Branch(&after_constant);
      int offset = masm_->pc_offset();
      int cp_offset = offset + Code::kHeaderSize - kHeapObjectTag;
      __ emit(0);
      masm_->label_at_put(label, offset);
      __ bind(&after_constant);
      if (is_int16(cp_offset)) {
        __ lw(a0, MemOperand(code_pointer(), cp_offset));
      } else {
        __ Addu(a0, code_pointer(), cp_offset);
        __ lw(a0, MemOperand(a0, 0));
      }
    }
    Push(a0);
    CheckStackLimit();
  }
  
  
  void RegExpMacroAssemblerMIPS::PushCurrentPosition() {
    Push(current_input_offset());
  }
  
  
  void RegExpMacroAssemblerMIPS::PushRegister(int register_index,
                                              StackCheckFlag check_stack_limit) {
    __ lw(a0, register_location(register_index));
    Push(a0);
    if (check_stack_limit) CheckStackLimit();
  }
  
  
  void RegExpMacroAssemblerMIPS::ReadCurrentPositionFromRegister(int reg) {
    __ lw(current_input_offset(), register_location(reg));
  }
  
  
  void RegExpMacroAssemblerMIPS::ReadStackPointerFromRegister(int reg) {
    __ lw(backtrack_stackpointer(), register_location(reg));
    __ lw(a0, MemOperand(frame_pointer(), kStackHighEnd));
    __ Addu(backtrack_stackpointer(), backtrack_stackpointer(), Operand(a0));
  }
  
  
  void RegExpMacroAssemblerMIPS::SetCurrentPositionFromEnd(int by) {
    Label after_position;
    __ Branch(&after_position,
              ge,
              current_input_offset(),
              Operand(-by * char_size()));
    __ li(current_input_offset(), -by * char_size());
    // On RegExp code entry (where this operation is used), the character before
    // the current position is expected to be already loaded.
    // We have advanced the position, so it's safe to read backwards.
    LoadCurrentCharacterUnchecked(-1, 1);
    __ bind(&after_position);
  }
  
  
  void RegExpMacroAssemblerMIPS::SetRegister(int register_index, int to) {
    DCHECK(register_index >= num_saved_registers_);  // Reserved for positions!
    __ li(a0, Operand(to));
    __ sw(a0, register_location(register_index));
  }
  
  
  bool RegExpMacroAssemblerMIPS::Succeed() {
    __ jmp(&success_label_);
    return global();
  }
  
  
  void RegExpMacroAssemblerMIPS::WriteCurrentPositionToRegister(int reg,
                                                                int cp_offset) {
    if (cp_offset == 0) {
      __ sw(current_input_offset(), register_location(reg));
    } else {
      __ Addu(a0, current_input_offset(), Operand(cp_offset * char_size()));
      __ sw(a0, register_location(reg));
    }
  }
  
  
  void RegExpMacroAssemblerMIPS::ClearRegisters(int reg_from, int reg_to) {
    DCHECK(reg_from <= reg_to);
    __ lw(a0, MemOperand(frame_pointer(), kStringStartMinusOne));
    for (int reg = reg_from; reg <= reg_to; reg++) {
      __ sw(a0, register_location(reg));
    }
  }
  
  
  void RegExpMacroAssemblerMIPS::WriteStackPointerToRegister(int reg) {
    __ lw(a1, MemOperand(frame_pointer(), kStackHighEnd));
    __ Subu(a0, backtrack_stackpointer(), a1);
    __ sw(a0, register_location(reg));
  }
  
  
  bool RegExpMacroAssemblerMIPS::CanReadUnaligned() {
    return false;
  }
  
  
  // Private methods:
  
  void RegExpMacroAssemblerMIPS::CallCheckStackGuardState(Register scratch) {
    DCHECK(!isolate()->ShouldLoadConstantsFromRootList());
    DCHECK(!masm_->options().isolate_independent_code);
  
    int stack_alignment = base::OS::ActivationFrameAlignment();
  
    // Align the stack pointer and save the original sp value on the stack.
    __ mov(scratch, sp);
    __ Subu(sp, sp, Operand(kPointerSize));
    DCHECK(base::bits::IsPowerOfTwo(stack_alignment));
    __ And(sp, sp, Operand(-stack_alignment));
    __ sw(scratch, MemOperand(sp));
  
    __ mov(a2, frame_pointer());
    // Code of self.
    __ li(a1, Operand(masm_->CodeObject()), CONSTANT_SIZE);
  
    // We need to make room for the return address on the stack.
    DCHECK(IsAligned(stack_alignment, kPointerSize));
    __ Subu(sp, sp, Operand(stack_alignment));
  
    // The stack pointer now points to cell where the return address will be
    // written. Arguments are in registers, meaning we treat the return address as
    // argument 5. Since DirectCEntry will handle allocating space for the C
    // argument slots, we don't need to care about that here. This is how the
    // stack will look (sp meaning the value of sp at this moment):
    // [sp + 3] - empty slot if needed for alignment.
    // [sp + 2] - saved sp.
    // [sp + 1] - second word reserved for return value.
    // [sp + 0] - first word reserved for return value.
  
    // a0 will point to the return address, placed by DirectCEntry.
    __ mov(a0, sp);
  
    ExternalReference stack_guard_check =
        ExternalReference::re_check_stack_guard_state(masm_->isolate());
    __ li(t9, Operand(stack_guard_check));
  
    if (FLAG_embedded_builtins) {
      EmbeddedData d = EmbeddedData::FromBlob();
      CHECK(Builtins::IsIsolateIndependent(Builtins::kDirectCEntry));
      Address entry = d.InstructionStartOfBuiltin(Builtins::kDirectCEntry);
      __ li(kScratchReg, Operand(entry, RelocInfo::OFF_HEAP_TARGET));
      __ Call(kScratchReg);
    } else {
      // TODO(v8:8519): Remove this once embedded builtins are on unconditionally.
      Handle<Code> code = BUILTIN_CODE(isolate(), DirectCEntry);
      __ li(kScratchReg,
            Operand(reinterpret_cast<intptr_t>(code.location()),
                    RelocInfo::CODE_TARGET),
            CONSTANT_SIZE);
      __ Call(kScratchReg);
    }
  
    // DirectCEntry allocated space for the C argument slots so we have to
    // drop them with the return address from the stack with loading saved sp.
    // At this point stack must look:
    // [sp + 7] - empty slot if needed for alignment.
    // [sp + 6] - saved sp.
    // [sp + 5] - second word reserved for return value.
    // [sp + 4] - first word reserved for return value.
    // [sp + 3] - C argument slot.
    // [sp + 2] - C argument slot.
    // [sp + 1] - C argument slot.
    // [sp + 0] - C argument slot.
    __ lw(sp, MemOperand(sp, stack_alignment + kCArgsSlotsSize));
  
    __ li(code_pointer(), Operand(masm_->CodeObject()));
  }
  
  
  // Helper function for reading a value out of a stack frame.
  template <typename T>
  static T& frame_entry(Address re_frame, int frame_offset) {
    return reinterpret_cast<T&>(Memory<int32_t>(re_frame + frame_offset));
  }
  
  
  template <typename T>
  static T* frame_entry_address(Address re_frame, int frame_offset) {
    return reinterpret_cast<T*>(re_frame + frame_offset);
  }
  
  int RegExpMacroAssemblerMIPS::CheckStackGuardState(Address* return_address,
                                                     Address raw_code,
                                                     Address re_frame) {
    Code re_code = Code::cast(ObjectPtr(raw_code));
    return NativeRegExpMacroAssembler::CheckStackGuardState(
        frame_entry<Isolate*>(re_frame, kIsolate),
        frame_entry<int>(re_frame, kStartIndex),
        frame_entry<int>(re_frame, kDirectCall) == 1, return_address, re_code,
        frame_entry_address<Address>(re_frame, kInputString),
        frame_entry_address<const byte*>(re_frame, kInputStart),
        frame_entry_address<const byte*>(re_frame, kInputEnd));
  }
  
  
  MemOperand RegExpMacroAssemblerMIPS::register_location(int register_index) {
    DCHECK(register_index < (1<<30));
    if (num_registers_ <= register_index) {
      num_registers_ = register_index + 1;
    }
    return MemOperand(frame_pointer(),
                      kRegisterZero - register_index * kPointerSize);
  }
  
  
  void RegExpMacroAssemblerMIPS::CheckPosition(int cp_offset,
                                               Label* on_outside_input) {
    if (cp_offset >= 0) {
      BranchOrBacktrack(on_outside_input, ge, current_input_offset(),
                        Operand(-cp_offset * char_size()));
    } else {
      __ lw(a1, MemOperand(frame_pointer(), kStringStartMinusOne));
      __ Addu(a0, current_input_offset(), Operand(cp_offset * char_size()));
      BranchOrBacktrack(on_outside_input, le, a0, Operand(a1));
    }
  }
  
  
  void RegExpMacroAssemblerMIPS::BranchOrBacktrack(Label* to,
                                                   Condition condition,
                                                   Register rs,
                                                   const Operand& rt) {
    if (condition == al) {  // Unconditional.
      if (to == nullptr) {
        Backtrack();
        return;
      }
      __ jmp(to);
      return;
    }
    if (to == nullptr) {
      __ Branch(&backtrack_label_, condition, rs, rt);
      return;
    }
    __ Branch(to, condition, rs, rt);
  }
  
  
  void RegExpMacroAssemblerMIPS::SafeCall(Label* to,
                                          Condition cond,
                                          Register rs,
                                          const Operand& rt) {
    __ BranchAndLink(to, cond, rs, rt);
  }
  
  
  void RegExpMacroAssemblerMIPS::SafeReturn() {
    __ pop(ra);
    __ Addu(t5, ra, Operand(masm_->CodeObject()));
    __ Jump(t5);
  }
  
  
  void RegExpMacroAssemblerMIPS::SafeCallTarget(Label* name) {
    __ bind(name);
    __ Subu(ra, ra, Operand(masm_->CodeObject()));
    __ push(ra);
  }
  
  
  void RegExpMacroAssemblerMIPS::Push(Register source) {
    DCHECK(source != backtrack_stackpointer());
    __ Addu(backtrack_stackpointer(),
            backtrack_stackpointer(),
            Operand(-kPointerSize));
    __ sw(source, MemOperand(backtrack_stackpointer()));
  }
  
  
  void RegExpMacroAssemblerMIPS::Pop(Register target) {
    DCHECK(target != backtrack_stackpointer());
    __ lw(target, MemOperand(backtrack_stackpointer()));
    __ Addu(backtrack_stackpointer(), backtrack_stackpointer(), kPointerSize);
  }
  
  
  void RegExpMacroAssemblerMIPS::CheckPreemption() {
    // Check for preemption.
    ExternalReference stack_limit =
        ExternalReference::address_of_stack_limit(masm_->isolate());
    __ li(a0, Operand(stack_limit));
    __ lw(a0, MemOperand(a0));
    SafeCall(&check_preempt_label_, ls, sp, Operand(a0));
  }
  
  
  void RegExpMacroAssemblerMIPS::CheckStackLimit() {
    ExternalReference stack_limit =
        ExternalReference::address_of_regexp_stack_limit(masm_->isolate());
  
    __ li(a0, Operand(stack_limit));
    __ lw(a0, MemOperand(a0));
    SafeCall(&stack_overflow_label_, ls, backtrack_stackpointer(), Operand(a0));
  }
  
  
  void RegExpMacroAssemblerMIPS::LoadCurrentCharacterUnchecked(int cp_offset,
                                                               int characters) {
    Register offset = current_input_offset();
    if (cp_offset != 0) {
      // t7 is not being used to store the capture start index at this point.
      __ Addu(t7, current_input_offset(), Operand(cp_offset * char_size()));
      offset = t7;
    }
    // We assume that we cannot do unaligned loads on MIPS, so this function
    // must only be used to load a single character at a time.
    DCHECK_EQ(1, characters);
    __ Addu(t5, end_of_input_address(), Operand(offset));
    if (mode_ == LATIN1) {
      __ lbu(current_character(), MemOperand(t5, 0));
    } else {
      DCHECK_EQ(UC16, mode_);
      __ lhu(current_character(), MemOperand(t5, 0));
    }
  }
  
  
  #undef __
  
  #endif  // V8_INTERPRETED_REGEXP
  
  }  // namespace internal
  }  // namespace v8
  
  #endif  // V8_TARGET_ARCH_MIPS
  