src/full-codegen.h

// 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.

#ifndef V8_FULL_CODEGEN_H_
#define V8_FULL_CODEGEN_H_

#include "v8.h"

#include "allocation.h"
#include "ast.h"
#include "code-stubs.h"
#include "codegen.h"
#include "compiler.h"

namespace v8 {
namespace internal {

// Forward declarations.
class JumpPatchSite;

// AST node visitor which can tell whether a given statement will be breakable
// when the code is compiled by the full compiler in the debugger. This means
// that there will be an IC (load/store/call) in the code generated for the
// debugger to piggybag on.
class BreakableStatementChecker: public AstVisitor {
 public:
  BreakableStatementChecker() : is_breakable_(false) {}

  void Check(Statement* stmt);
  void Check(Expression* stmt);

  bool is_breakable() { return is_breakable_; }

 private:
  // AST node visit functions.
#define DECLARE_VISIT(type) virtual void Visit##type(type* node);
  AST_NODE_LIST(DECLARE_VISIT)
#undef DECLARE_VISIT

  bool is_breakable_;

  DISALLOW_COPY_AND_ASSIGN(BreakableStatementChecker);
};


// -----------------------------------------------------------------------------
// Full code generator.

class FullCodeGenerator: public AstVisitor {
 public:
  enum State {
    NO_REGISTERS,
    TOS_REG
  };

  explicit FullCodeGenerator(MacroAssembler* masm)
      : masm_(masm),
        info_(NULL),
        scope_(NULL),
        nesting_stack_(NULL),
        loop_depth_(0),
        stack_height_(0),
        context_(NULL),
        bailout_entries_(0),
        stack_checks_(2),  // There's always at least one.
        forward_bailout_stack_(NULL),
        forward_bailout_pending_(NULL) {
  }

  static bool MakeCode(CompilationInfo* info);

  void Generate(CompilationInfo* info);
  void PopulateDeoptimizationData(Handle<Code> code);

  class StateField : public BitField<State, 0, 8> { };
  class PcField    : public BitField<unsigned, 8, 32-8> { };

  static const char* State2String(State state) {
    switch (state) {
      case NO_REGISTERS: return "NO_REGISTERS";
      case TOS_REG: return "TOS_REG";
    }
    UNREACHABLE();
    return NULL;
  }

 private:
  class Breakable;
  class Iteration;

  class TestContext;

  class NestedStatement BASE_EMBEDDED {
   public:
    explicit NestedStatement(FullCodeGenerator* codegen) : codegen_(codegen) {
      // Link into codegen's nesting stack.
      previous_ = codegen->nesting_stack_;
      codegen->nesting_stack_ = this;
    }
    virtual ~NestedStatement() {
      // Unlink from codegen's nesting stack.
      ASSERT_EQ(this, codegen_->nesting_stack_);
      codegen_->nesting_stack_ = previous_;
    }

    virtual Breakable* AsBreakable() { return NULL; }
    virtual Iteration* AsIteration() { return NULL; }

    virtual bool IsContinueTarget(Statement* target) { return false; }
    virtual bool IsBreakTarget(Statement* target) { return false; }

    // Notify the statement that we are exiting it via break, continue, or
    // return and give it a chance to generate cleanup code.  Return the
    // next outer statement in the nesting stack.  We accumulate in
    // *stack_depth the amount to drop the stack and in *context_length the
    // number of context chain links to unwind as we traverse the nesting
    // stack from an exit to its target.
    virtual NestedStatement* Exit(int* stack_depth, int* context_length) {
      return previous_;
    }

 protected:
    MacroAssembler* masm() { return codegen_->masm(); }

    FullCodeGenerator* codegen_;
    NestedStatement* previous_;
    DISALLOW_COPY_AND_ASSIGN(NestedStatement);
  };

  // A breakable statement such as a block.
  class Breakable : public NestedStatement {
   public:
    Breakable(FullCodeGenerator* codegen, BreakableStatement* statement)
        : NestedStatement(codegen), statement_(statement) {
    }
    virtual ~Breakable() {}

    virtual Breakable* AsBreakable() { return this; }
    virtual bool IsBreakTarget(Statement* target) {
      return statement() == target;
    }

    BreakableStatement* statement() { return statement_; }
    Label* break_label() { return &break_label_; }

   private:
    BreakableStatement* statement_;
    Label break_label_;
  };

  // An iteration statement such as a while, for, or do loop.
  class Iteration : public Breakable {
   public:
    Iteration(FullCodeGenerator* codegen, IterationStatement* statement)
        : Breakable(codegen, statement) {
    }
    virtual ~Iteration() {}

    virtual Iteration* AsIteration() { return this; }
    virtual bool IsContinueTarget(Statement* target) {
      return statement() == target;
    }

    Label* continue_label() { return &continue_label_; }

   private:
    Label continue_label_;
  };

  // The try block of a try/catch statement.
  class TryCatch : public NestedStatement {
   public:
    explicit TryCatch(FullCodeGenerator* codegen) : NestedStatement(codegen) {
    }
    virtual ~TryCatch() {}

    virtual NestedStatement* Exit(int* stack_depth, int* context_length);
  };

  // The try block of a try/finally statement.
  class TryFinally : public NestedStatement {
   public:
    TryFinally(FullCodeGenerator* codegen, Label* finally_entry)
        : NestedStatement(codegen), finally_entry_(finally_entry) {
    }
    virtual ~TryFinally() {}

    virtual NestedStatement* Exit(int* stack_depth, int* context_length);

   private:
    Label* finally_entry_;
  };

  // The finally block of a try/finally statement.
  class Finally : public NestedStatement {
   public:
    static const int kElementCount = 2;

    explicit Finally(FullCodeGenerator* codegen) : NestedStatement(codegen) { }
    virtual ~Finally() {}

    virtual NestedStatement* Exit(int* stack_depth, int* context_length) {
      *stack_depth += kElementCount;
      return previous_;
    }
  };

  // The body of a for/in loop.
  class ForIn : public Iteration {
   public:
    static const int kElementCount = 5;

    ForIn(FullCodeGenerator* codegen, ForInStatement* statement)
        : Iteration(codegen, statement) {
    }
    virtual ~ForIn() {}

    virtual NestedStatement* Exit(int* stack_depth, int* context_length) {
      *stack_depth += kElementCount;
      return previous_;
    }
  };


  // The body of a with or catch.
  class WithOrCatch : public NestedStatement {
   public:
    explicit WithOrCatch(FullCodeGenerator* codegen)
        : NestedStatement(codegen) {
    }
    virtual ~WithOrCatch() {}

    virtual NestedStatement* Exit(int* stack_depth, int* context_length) {
      ++(*context_length);
      return previous_;
    }
  };

  // The forward bailout stack keeps track of the expressions that can
  // bail out to just before the control flow is split in a child
  // node. The stack elements are linked together through the parent
  // link when visiting expressions in test contexts after requesting
  // bailout in child forwarding.
  class ForwardBailoutStack BASE_EMBEDDED {
   public:
    ForwardBailoutStack(Expression* expr, ForwardBailoutStack* parent)
        : expr_(expr), parent_(parent) { }

    Expression* expr() const { return expr_; }
    ForwardBailoutStack* parent() const { return parent_; }

   private:
    Expression* const expr_;
    ForwardBailoutStack* const parent_;
  };

  // Type of a member function that generates inline code for a native function.
  typedef void (FullCodeGenerator::*InlineFunctionGenerator)
      (ZoneList<Expression*>*);

  static const InlineFunctionGenerator kInlineFunctionGenerators[];

  // A platform-specific utility to overwrite the accumulator register
  // with a GC-safe value.
  void ClearAccumulator();

  // Compute the frame pointer relative offset for a given local or
  // parameter slot.
  int SlotOffset(Slot* slot);

  // Determine whether or not to inline the smi case for the given
  // operation.
  bool ShouldInlineSmiCase(Token::Value op);

  // Helper function to convert a pure value into a test context.  The value
  // is expected on the stack or the accumulator, depending on the platform.
  // See the platform-specific implementation for details.
  void DoTest(Expression* condition,
              Label* if_true,
              Label* if_false,
              Label* fall_through);
  void DoTest(const TestContext* context);

  // Helper function to split control flow and avoid a branch to the
  // fall-through label if it is set up.
#ifdef V8_TARGET_ARCH_MIPS
  void Split(Condition cc,
             Register lhs,
             const Operand&  rhs,
             Label* if_true,
             Label* if_false,
             Label* fall_through);
#else  // All non-mips arch.
  void Split(Condition cc,
             Label* if_true,
             Label* if_false,
             Label* fall_through);
#endif  // V8_TARGET_ARCH_MIPS

  void Move(Slot* dst, Register source, Register scratch1, Register scratch2);
  void Move(Register dst, Slot* source);

  // Return an operand used to read/write to a known (ie, non-LOOKUP) slot.
  // May emit code to traverse the context chain, destroying the scratch
  // register.
  MemOperand EmitSlotSearch(Slot* slot, Register scratch);

  // Forward the bailout responsibility for the given expression to
  // the next child visited (which must be in a test context).
  void ForwardBailoutToChild(Expression* expr);

  void VisitForEffect(Expression* expr) {
    EffectContext context(this);
    VisitInCurrentContext(expr);
  }

  void VisitForAccumulatorValue(Expression* expr) {
    AccumulatorValueContext context(this);
    VisitInCurrentContext(expr);
  }

  void VisitForStackValue(Expression* expr) {
    StackValueContext context(this);
    VisitInCurrentContext(expr);
  }

  void VisitForControl(Expression* expr,
                       Label* if_true,
                       Label* if_false,
                       Label* fall_through) {
    TestContext context(this, expr, if_true, if_false, fall_through);
    VisitInCurrentContext(expr);
  }

  void VisitDeclarations(ZoneList<Declaration*>* declarations);
  void DeclareGlobals(Handle<FixedArray> pairs);

  // Try to perform a comparison as a fast inlined literal compare if
  // the operands allow it.  Returns true if the compare operations
  // has been matched and all code generated; false otherwise.
  bool TryLiteralCompare(CompareOperation* compare,
                         Label* if_true,
                         Label* if_false,
                         Label* fall_through);

  // Platform-specific code for comparing the type of a value with
  // a given literal string.
  void EmitLiteralCompareTypeof(Expression* expr,
                                Handle<String> check,
                                Label* if_true,
                                Label* if_false,
                                Label* fall_through);

  // Platform-specific code for strict equality comparison with
  // the undefined value.
  void EmitLiteralCompareUndefined(Expression* expr,
                                   Label* if_true,
                                   Label* if_false,
                                   Label* fall_through);

  // Bailout support.
  void PrepareForBailout(Expression* node, State state);
  void PrepareForBailoutForId(int id, State state);

  // Record a call's return site offset, used to rebuild the frame if the
  // called function was inlined at the site.
  void RecordJSReturnSite(Call* call);

  // Prepare for bailout before a test (or compare) and branch.  If
  // should_normalize, then the following comparison will not handle the
  // canonical JS true value so we will insert a (dead) test against true at
  // the actual bailout target from the optimized code. If not
  // should_normalize, the true and false labels are ignored.
  void PrepareForBailoutBeforeSplit(State state,
                                    bool should_normalize,
                                    Label* if_true,
                                    Label* if_false);

  // Platform-specific code for a variable, constant, or function
  // declaration.  Functions have an initial value.
  void EmitDeclaration(Variable* variable,
                       Variable::Mode mode,
                       FunctionLiteral* function);

  // Platform-specific code for checking the stack limit at the back edge of
  // a loop.
  void EmitStackCheck(IterationStatement* stmt);
  // Record the OSR AST id corresponding to a stack check in the code.
  void RecordStackCheck(int osr_ast_id);
  // Emit a table of stack check ids and pcs into the code stream.  Return
  // the offset of the start of the table.
  unsigned EmitStackCheckTable();

  // Platform-specific return sequence
  void EmitReturnSequence();

  // Platform-specific code sequences for calls
  void EmitCallWithStub(Call* expr, CallFunctionFlags flags);
  void EmitCallWithIC(Call* expr, Handle<Object> name, RelocInfo::Mode mode);
  void EmitKeyedCallWithIC(Call* expr, Expression* key);

  // Platform-specific code for inline runtime calls.
  InlineFunctionGenerator FindInlineFunctionGenerator(Runtime::FunctionId id);

  void EmitInlineRuntimeCall(CallRuntime* expr);

#define EMIT_INLINE_RUNTIME_CALL(name, x, y) \
  void Emit##name(ZoneList<Expression*>* arguments);
  INLINE_FUNCTION_LIST(EMIT_INLINE_RUNTIME_CALL)
  INLINE_RUNTIME_FUNCTION_LIST(EMIT_INLINE_RUNTIME_CALL)
#undef EMIT_INLINE_RUNTIME_CALL

  // Platform-specific code for loading variables.
  void EmitLoadGlobalSlotCheckExtensions(Slot* slot,
                                         TypeofState typeof_state,
                                         Label* slow);
  MemOperand ContextSlotOperandCheckExtensions(Slot* slot, Label* slow);
  void EmitDynamicLoadFromSlotFastCase(Slot* slot,
                                       TypeofState typeof_state,
                                       Label* slow,
                                       Label* done);
  void EmitVariableLoad(VariableProxy* proxy);

  enum ResolveEvalFlag {
    SKIP_CONTEXT_LOOKUP,
    PERFORM_CONTEXT_LOOKUP
  };

  // Expects the arguments and the function already pushed.
  void EmitResolvePossiblyDirectEval(ResolveEvalFlag flag, int arg_count);

  // Platform-specific support for allocating a new closure based on
  // the given function info.
  void EmitNewClosure(Handle<SharedFunctionInfo> info, bool pretenure);

  // Platform-specific support for compiling assignments.

  // Load a value from a named property.
  // The receiver is left on the stack by the IC.
  void EmitNamedPropertyLoad(Property* expr);

  // Load a value from a keyed property.
  // The receiver and the key is left on the stack by the IC.
  void EmitKeyedPropertyLoad(Property* expr);

  // Apply the compound assignment operator. Expects the left operand on top
  // of the stack and the right one in the accumulator.
  void EmitBinaryOp(BinaryOperation* expr,
                    Token::Value op,
                    OverwriteMode mode);

  // Helper functions for generating inlined smi code for certain
  // binary operations.
  void EmitInlineSmiBinaryOp(BinaryOperation* expr,
                             Token::Value op,
                             OverwriteMode mode,
                             Expression* left,
                             Expression* right);

  // Assign to the given expression as if via '='. The right-hand-side value
  // is expected in the accumulator.
  void EmitAssignment(Expression* expr, int bailout_ast_id);

  // Complete a variable assignment.  The right-hand-side value is expected
  // in the accumulator.
  void EmitVariableAssignment(Variable* var,
                              Token::Value op);

  // Complete a named property assignment.  The receiver is expected on top
  // of the stack and the right-hand-side value in the accumulator.
  void EmitNamedPropertyAssignment(Assignment* expr);

  // Complete a keyed property assignment.  The receiver and key are
  // expected on top of the stack and the right-hand-side value in the
  // accumulator.
  void EmitKeyedPropertyAssignment(Assignment* expr);

  void SetFunctionPosition(FunctionLiteral* fun);
  void SetReturnPosition(FunctionLiteral* fun);
  void SetStatementPosition(Statement* stmt);
  void SetExpressionPosition(Expression* expr, int pos);
  void SetStatementPosition(int pos);
  void SetSourcePosition(int pos);

  // Non-local control flow support.
  void EnterFinallyBlock();
  void ExitFinallyBlock();

  // Loop nesting counter.
  int loop_depth() { return loop_depth_; }
  void increment_loop_depth() { loop_depth_++; }
  void decrement_loop_depth() {
    ASSERT(loop_depth_ > 0);
    loop_depth_--;
  }

#if defined(V8_TARGET_ARCH_IA32)
  int stack_height() { return stack_height_; }
  void set_stack_height(int depth) { stack_height_ = depth; }
  void increment_stack_height() { stack_height_++; }
  void increment_stack_height(int delta) { stack_height_ += delta; }
  void decrement_stack_height() {
    if (FLAG_verify_stack_height) {
      ASSERT(stack_height_ > 0);
    }
    stack_height_--;
  }
  void decrement_stack_height(int delta) {
    stack_height_-= delta;
    if (FLAG_verify_stack_height) {
      ASSERT(stack_height_ >= 0);
    }
  }
  // Call this function only if FLAG_verify_stack_height is true.
  void verify_stack_height();  // Generates a runtime check of esp - ebp.
#else
  int stack_height() { return 0; }
  void set_stack_height(int depth) {}
  void increment_stack_height() {}
  void increment_stack_height(int delta) {}
  void decrement_stack_height() {}
  void decrement_stack_height(int delta) {}
  void verify_stack_height() {}
#endif  // V8_TARGET_ARCH_IA32

  MacroAssembler* masm() { return masm_; }

  class ExpressionContext;
  const ExpressionContext* context() { return context_; }
  void set_new_context(const ExpressionContext* context) { context_ = context; }

  Handle<Script> script() { return info_->script(); }
  bool is_eval() { return info_->is_eval(); }
  bool is_strict_mode() { return function()->strict_mode(); }
  StrictModeFlag strict_mode_flag() {
    return is_strict_mode() ? kStrictMode : kNonStrictMode;
  }
  FunctionLiteral* function() { return info_->function(); }
  Scope* scope() { return scope_; }

  static Register result_register();
  static Register context_register();

  // Set fields in the stack frame. Offsets are the frame pointer relative
  // offsets defined in, e.g., StandardFrameConstants.
  void StoreToFrameField(int frame_offset, Register value);

  // Load a value from the current context. Indices are defined as an enum
  // in v8::internal::Context.
  void LoadContextField(Register dst, int context_index);

  // Push the function argument for the runtime functions PushWithContext
  // and PushCatchContext.
  void PushFunctionArgumentForContextAllocation();

  // AST node visit functions.
#define DECLARE_VISIT(type) virtual void Visit##type(type* node);
  AST_NODE_LIST(DECLARE_VISIT)
#undef DECLARE_VISIT

  void EmitUnaryOperation(UnaryOperation* expr, const char* comment);

  void VisitComma(BinaryOperation* expr);
  void VisitLogicalExpression(BinaryOperation* expr);
  void VisitArithmeticExpression(BinaryOperation* expr);
  void VisitInCurrentContext(Expression* expr);

  void VisitForTypeofValue(Expression* expr);

  struct BailoutEntry {
    unsigned id;
    unsigned pc_and_state;
  };


  class ExpressionContext BASE_EMBEDDED {
   public:
    explicit ExpressionContext(FullCodeGenerator* codegen)
        : masm_(codegen->masm()), old_(codegen->context()), codegen_(codegen) {
      codegen->set_new_context(this);
    }

    virtual ~ExpressionContext() {
      codegen_->set_new_context(old_);
      if (FLAG_verify_stack_height) {
        ASSERT_EQ(expected_stack_height_, codegen()->stack_height());
        codegen()->verify_stack_height();
      }
    }

    Isolate* isolate() const { return codegen_->isolate(); }

    // Convert constant control flow (true or false) to the result expected for
    // this expression context.
    virtual void Plug(bool flag) const = 0;

    // Emit code to convert a pure value (in a register, slot, as a literal,
    // or on top of the stack) into the result expected according to this
    // expression context.
    virtual void Plug(Register reg) const = 0;
    virtual void Plug(Slot* slot) const = 0;
    virtual void Plug(Handle<Object> lit) const = 0;
    virtual void Plug(Heap::RootListIndex index) const = 0;
    virtual void PlugTOS() const = 0;

    // Emit code to convert pure control flow to a pair of unbound labels into
    // the result expected according to this expression context.  The
    // implementation will bind both labels unless it's a TestContext, which
    // won't bind them at this point.
    virtual void Plug(Label* materialize_true,
                      Label* materialize_false) const = 0;

    // Emit code to discard count elements from the top of stack, then convert
    // a pure value into the result expected according to this expression
    // context.
    virtual void DropAndPlug(int count, Register reg) const = 0;

    // Set up branch labels for a test expression.  The three Label** parameters
    // are output parameters.
    virtual void PrepareTest(Label* materialize_true,
                             Label* materialize_false,
                             Label** if_true,
                             Label** if_false,
                             Label** fall_through) const = 0;

    // Returns true if we are evaluating only for side effects (ie if the result
    // will be discarded).
    virtual bool IsEffect() const { return false; }

    // Returns true if we are evaluating for the value (in accu/on stack).
    virtual bool IsAccumulatorValue() const { return false; }
    virtual bool IsStackValue() const { return false; }

    // Returns true if we are branching on the value rather than materializing
    // it.  Only used for asserts.
    virtual bool IsTest() const { return false; }

   protected:
    FullCodeGenerator* codegen() const { return codegen_; }
    MacroAssembler* masm() const { return masm_; }
    MacroAssembler* masm_;
    int expected_stack_height_;  // The expected stack height esp - ebp on exit.

   private:
    const ExpressionContext* old_;
    FullCodeGenerator* codegen_;
  };

  class AccumulatorValueContext : public ExpressionContext {
   public:
    explicit AccumulatorValueContext(FullCodeGenerator* codegen)
        : ExpressionContext(codegen) {
      expected_stack_height_ = codegen->stack_height();
    }

    virtual void Plug(bool flag) const;
    virtual void Plug(Register reg) const;
    virtual void Plug(Label* materialize_true, Label* materialize_false) const;
    virtual void Plug(Slot* slot) const;
    virtual void Plug(Handle<Object> lit) const;
    virtual void Plug(Heap::RootListIndex) const;
    virtual void PlugTOS() const;
    virtual void DropAndPlug(int count, Register reg) const;
    virtual void PrepareTest(Label* materialize_true,
                             Label* materialize_false,
                             Label** if_true,
                             Label** if_false,
                             Label** fall_through) const;
    virtual bool IsAccumulatorValue() const { return true; }
  };

  class StackValueContext : public ExpressionContext {
   public:
    explicit StackValueContext(FullCodeGenerator* codegen)
        : ExpressionContext(codegen) {
      expected_stack_height_ = codegen->stack_height() + 1;
    }

    virtual void Plug(bool flag) const;
    virtual void Plug(Register reg) const;
    virtual void Plug(Label* materialize_true, Label* materialize_false) const;
    virtual void Plug(Slot* slot) const;
    virtual void Plug(Handle<Object> lit) const;
    virtual void Plug(Heap::RootListIndex) const;
    virtual void PlugTOS() const;
    virtual void DropAndPlug(int count, Register reg) const;
    virtual void PrepareTest(Label* materialize_true,
                             Label* materialize_false,
                             Label** if_true,
                             Label** if_false,
                             Label** fall_through) const;
    virtual bool IsStackValue() const { return true; }
  };

  class TestContext : public ExpressionContext {
   public:
    TestContext(FullCodeGenerator* codegen,
                Expression* condition,
                Label* true_label,
                Label* false_label,
                Label* fall_through)
        : ExpressionContext(codegen),
          condition_(condition),
          true_label_(true_label),
          false_label_(false_label),
          fall_through_(fall_through) {
      expected_stack_height_ = codegen->stack_height();
    }

    static const TestContext* cast(const ExpressionContext* context) {
      ASSERT(context->IsTest());
      return reinterpret_cast<const TestContext*>(context);
    }

    Expression* condition() const { return condition_; }
    Label* true_label() const { return true_label_; }
    Label* false_label() const { return false_label_; }
    Label* fall_through() const { return fall_through_; }

    virtual void Plug(bool flag) const;
    virtual void Plug(Register reg) const;
    virtual void Plug(Label* materialize_true, Label* materialize_false) const;
    virtual void Plug(Slot* slot) const;
    virtual void Plug(Handle<Object> lit) const;
    virtual void Plug(Heap::RootListIndex) const;
    virtual void PlugTOS() const;
    virtual void DropAndPlug(int count, Register reg) const;
    virtual void PrepareTest(Label* materialize_true,
                             Label* materialize_false,
                             Label** if_true,
                             Label** if_false,
                             Label** fall_through) const;
    virtual bool IsTest() const { return true; }

   private:
    Expression* condition_;
    Label* true_label_;
    Label* false_label_;
    Label* fall_through_;
  };

  class EffectContext : public ExpressionContext {
   public:
    explicit EffectContext(FullCodeGenerator* codegen)
        : ExpressionContext(codegen) {
      expected_stack_height_ = codegen->stack_height();
    }


    virtual void Plug(bool flag) const;
    virtual void Plug(Register reg) const;
    virtual void Plug(Label* materialize_true, Label* materialize_false) const;
    virtual void Plug(Slot* slot) const;
    virtual void Plug(Handle<Object> lit) const;
    virtual void Plug(Heap::RootListIndex) const;
    virtual void PlugTOS() const;
    virtual void DropAndPlug(int count, Register reg) const;
    virtual void PrepareTest(Label* materialize_true,
                             Label* materialize_false,
                             Label** if_true,
                             Label** if_false,
                             Label** fall_through) const;
    virtual bool IsEffect() const { return true; }
  };

  MacroAssembler* masm_;
  CompilationInfo* info_;
  Scope* scope_;
  Label return_label_;
  NestedStatement* nesting_stack_;
  int loop_depth_;
  int stack_height_;
  const ExpressionContext* context_;
  ZoneList<BailoutEntry> bailout_entries_;
  ZoneList<BailoutEntry> stack_checks_;
  ForwardBailoutStack* forward_bailout_stack_;
  ForwardBailoutStack* forward_bailout_pending_;

  friend class NestedStatement;

  DISALLOW_COPY_AND_ASSIGN(FullCodeGenerator);
};


} }  // namespace v8::internal

#endif  // V8_FULL_CODEGEN_H_