text: /*
   * Copyright (C) 2015-2016 Apple Inc. All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   * 2. 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.
   *
   * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``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 APPLE INC. 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. 
   */
  
  #pragma once
  
  #if ENABLE(B3_JIT)
  
  #include "B3ConstrainedValue.h"
  #include "B3Value.h"
  #include "B3ValueRep.h"
  #include "CCallHelpers.h"
  #include "RegisterSet.h"
  #include <wtf/SharedTask.h>
  
  namespace JSC { namespace B3 {
  
  class StackmapGenerationParams;
  
  typedef void StackmapGeneratorFunction(CCallHelpers&, const StackmapGenerationParams&);
  typedef SharedTask<StackmapGeneratorFunction> StackmapGenerator;
  
  class JS_EXPORT_PRIVATE StackmapValue : public Value {
  public:
      static bool accepts(Kind kind)
      {
          // This needs to include opcodes of all subclasses.
          switch (kind.opcode()) {
          case CheckAdd:
          case CheckSub:
          case CheckMul:
          case Check:
          case Patchpoint:
              return true;
          default:
              return false;
          }
      }
  
      ~StackmapValue();
  
      // Use this to add children. Note that you could also add children by doing
      // children().append(). That will work fine, but it's not recommended.
      void append(const ConstrainedValue& value)
      {
          append(value.value(), value.rep());
      }
  
      void append(Value*, const ValueRep&);
  
      template<typename VectorType>
      void appendVector(const VectorType& vector)
      {
          for (const auto& value : vector)
              append(value);
      }
  
      // Helper for appending a bunch of values with some ValueRep.
      template<typename VectorType>
      void appendVectorWithRep(const VectorType& vector, const ValueRep& rep)
      {
          for (Value* value : vector)
              append(value, rep);
      }
  
      // Helper for appending cold any's. This often used by clients to implement OSR.
      template<typename VectorType>
      void appendColdAnys(const VectorType& vector)
      {
          appendVectorWithRep(vector, ValueRep::ColdAny);
      }
      template<typename VectorType>
      void appendLateColdAnys(const VectorType& vector)
      {
          appendVectorWithRep(vector, ValueRep::LateColdAny);
      }
  
      // This is a helper for something you might do a lot of: append a value that should be constrained
      // to SomeRegister.
      void appendSomeRegister(Value*);
  
      const Vector<ValueRep>& reps() const { return m_reps; }
  
      // Stackmaps allow you to specify that the operation may clobber some registers. Clobbering a register
      // means that the operation appears to store a value into the register, but the compiler doesn't
      // assume to know anything about what kind of value might have been stored. In B3's model of
      // execution, registers are read or written at instruction boundaries rather than inside the
      // instructions themselves. A register could be read or written immediately before the instruction
      // executes, or immediately after. Note that at a boundary between instruction A and instruction B we
      // simultaneously look at what A does after it executes and what B does before it executes. This is
      // because when the compiler considers what happens to registers, it views the boundary between two
      // instructions as a kind of atomic point where the late effects of A happen at the same time as the
      // early effects of B.
      //
      // The compiler views a stackmap as a single instruction, even though of course the stackmap may be
      // composed of any number of instructions (if it's a Patchpoint). You can claim that a stackmap value
      // clobbers a set of registers before the stackmap's instruction or after. Clobbering before is called
      // early clobber, while clobbering after is called late clobber.
      //
      // This is quite flexible but it has its limitations. Any register listed as an early clobber will
      // interfere with all uses of the stackmap. Any register listed as a late clobber will interfere with
      // all defs of the stackmap (i.e. the result). This means that it's currently not possible to claim
      // to clobber a register while still allowing that register to be used for both an input and an output
      // of the instruction. It just so happens that B3's sole client (the FTL) currently never wants to
      // convey such a constraint, but it will want it eventually (FIXME:
      // https://bugs.webkit.org/show_bug.cgi?id=151823).
      //
      // Note that a common use case of early clobber sets is to indicate that this is the set of registers
      // that shall not be used for inputs to the value. But B3 supports two different ways of specifying
      // this, the other being LateUse in combination with late clobber (not yet available to stackmaps
      // directly, FIXME: https://bugs.webkit.org/show_bug.cgi?id=151335). A late use makes the use of that
      // value appear to happen after the instruction. This means that a late use cannot use the same
      // register as the result and it cannot use the same register as either early or late clobbered
      // registers. Late uses are usually a better way of saying that a clobbered register cannot be used
      // for an input. Early clobber means that some register(s) interfere with *all* inputs, while LateUse
      // means that some value interferes with whatever is live after the instruction. Below is a list of
      // examples of how the FTL can handle its various kinds of scenarios using a combination of early
      // clobber, late clobber, and late use. These examples are for X86_64, w.l.o.g.
      //
      // Basic ById patchpoint: Early and late clobber of r11. Early clobber prevents any inputs from using
      // r11 since that would mess with the MacroAssembler's assumptions when we
      // AllowMacroScratchRegisterUsage. Late clobber tells B3 that the patchpoint may overwrite r11.
      //
      // ById patchpoint in a try block with some live state: This might throw an exception after already
      // assigning to the result. So, this should LateUse all stackmap values to ensure that the stackmap
      // values don't interfere with the result. Note that we do not LateUse the non-OSR inputs of the ById
      // since LateUse implies that the use is cold: the register allocator will assume that the use is not
      // important for the critical path. Also, early and late clobber of r11.
      //
      // Basic ByIdFlush patchpoint: We could do Flush the same way we did it with LLVM: ignore it and let
      // PolymorphicAccess figure it out. Or, we could add internal clobber support (FIXME:
      // https://bugs.webkit.org/show_bug.cgi?id=151823). Or, we could do it by early clobbering r11, late
      // clobbering all volatile registers, and constraining the result to some register. Or, we could do
      // that but leave the result constrained to SomeRegister, which will cause it to use a callee-save
      // register. Internal clobber support would allow us to use SomeRegister while getting the result into
      // a volatile register.
      //
      // ByIdFlush patchpoint in a try block with some live state: LateUse all for-OSR stackmap values,
      // early clobber of r11 to prevent the other inputs from using r11, and late clobber of all volatile
      // registers to make way for the call. To handle the result, we could do any of what is listed in the
      // previous paragraph.
      //
      // Basic JS call: Force all non-OSR inputs into specific locations (register, stack, whatever).
      // All volatile registers are late-clobbered. The output is constrained to a register as well.
      //
      // JS call in a try block with some live state: LateUse all for-OSR stackmap values, fully constrain
      // all non-OSR inputs and the result, and late clobber all volatile registers.
      //
      // JS tail call: Pass all inputs as a warm variant of Any (FIXME:
      // https://bugs.webkit.org/show_bug.cgi?id=151811).
      //
      // Note that we cannot yet do all of these things because although Air already supports all of these
      // various forms of uses (LateUse and warm unconstrained use), B3 doesn't yet expose all of it. The
      // bugs are:
      // https://bugs.webkit.org/show_bug.cgi?id=151335 (LateUse)
      // https://bugs.webkit.org/show_bug.cgi?id=151811 (warm Any)
      void clobberEarly(const RegisterSet& set)
      {
          m_earlyClobbered.merge(set);
      }
  
      void clobberLate(const RegisterSet& set)
      {
          m_lateClobbered.merge(set);
      }
  
      void clobber(const RegisterSet& set)
      {
          clobberEarly(set);
          clobberLate(set);
      }
  
      RegisterSet& earlyClobbered() { return m_earlyClobbered; }
      RegisterSet& lateClobbered() { return m_lateClobbered; }
      const RegisterSet& earlyClobbered() const { return m_earlyClobbered; }
      const RegisterSet& lateClobbered() const { return m_lateClobbered; }
  
      void setGenerator(RefPtr<StackmapGenerator> generator)
      {
          m_generator = generator;
      }
  
      template<typename Functor>
      void setGenerator(const Functor& functor)
      {
          m_generator = createSharedTask<StackmapGeneratorFunction>(functor);
      }
  
      RefPtr<StackmapGenerator> generator() const { return m_generator; }
  
      ConstrainedValue constrainedChild(unsigned index) const
      {
          return ConstrainedValue(child(index), index < m_reps.size() ? m_reps[index] : ValueRep::ColdAny);
      }
  
      void setConstrainedChild(unsigned index, const ConstrainedValue&);
      
      void setConstraint(unsigned index, const ValueRep&);
  
      class ConstrainedValueCollection {
      public:
          ConstrainedValueCollection(const StackmapValue& value)
              : m_value(value)
          {
          }
  
          unsigned size() const { return m_value.numChildren(); }
          
          ConstrainedValue at(unsigned index) const { return m_value.constrainedChild(index); }
  
          ConstrainedValue operator[](unsigned index) const { return at(index); }
  
          class iterator {
          public:
              iterator()
                  : m_collection(nullptr)
                  , m_index(0)
              {
              }
  
              iterator(const ConstrainedValueCollection& collection, unsigned index)
                  : m_collection(&collection)
                  , m_index(index)
              {
              }
  
              ConstrainedValue operator*() const
              {
                  return m_collection->at(m_index);
              }
  
              iterator& operator++()
              {
                  m_index++;
                  return *this;
              }
  
              bool operator==(const iterator& other) const
              {
                  ASSERT(m_collection == other.m_collection);
                  return m_index == other.m_index;
              }
  
              bool operator!=(const iterator& other) const
              {
                  return !(*this == other);
              }
              
          private:
              const ConstrainedValueCollection* m_collection;
              unsigned m_index;
          };
  
          iterator begin() const { return iterator(*this, 0); }
          iterator end() const { return iterator(*this, size()); }
  
      private:
          const StackmapValue& m_value;
      };
  
      ConstrainedValueCollection constrainedChildren() const
      {
          return ConstrainedValueCollection(*this);
      }
  
  protected:
      void dumpChildren(CommaPrinter&, PrintStream&) const override;
      void dumpMeta(CommaPrinter&, PrintStream&) const override;
  
      StackmapValue(CheckedOpcodeTag, Kind, Type, Origin);
  
  private:
      friend class CheckSpecial;
      friend class PatchpointSpecial;
      friend class StackmapGenerationParams;
      friend class StackmapSpecial;
      
      Vector<ValueRep> m_reps;
      RefPtr<StackmapGenerator> m_generator;
      RegisterSet m_earlyClobbered;
      RegisterSet m_lateClobbered;
      RegisterSet m_usedRegisters; // Stackmaps could be further duplicated by Air, but that's unlikely, so we just merge the used registers sets if that were to happen.
  };
  
  } } // namespace JSC::B3
  
  #endif // ENABLE(B3_JIT)
  