src/mips/virtual-frame-mips.h

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#ifndef V8_MIPS_VIRTUAL_FRAME_MIPS_H_
#define V8_MIPS_VIRTUAL_FRAME_MIPS_H_

#include "register-allocator.h"

namespace v8 {
namespace internal {

// This dummy class is only used to create invalid virtual frames.
extern class InvalidVirtualFrameInitializer {}* kInvalidVirtualFrameInitializer;


// -------------------------------------------------------------------------
// Virtual frames
//
// The virtual frame is an abstraction of the physical stack frame. It
// encapsulates the parameters, frame-allocated locals, and the expression
// stack. It supports push/pop operations on the expression stack, as well
// as random access to the expression stack elements, locals, and
// parameters.

class VirtualFrame : public ZoneObject {
 public:
  class RegisterAllocationScope;
  // A utility class to introduce a scope where the virtual frame is
  // expected to remain spilled. The constructor spills the code
  // generator's current frame, and keeps it spilled.
  class SpilledScope BASE_EMBEDDED {
   public:
    explicit SpilledScope(VirtualFrame* frame)
      : old_is_spilled_(
          Isolate::Current()->is_virtual_frame_in_spilled_scope()) {
      if (frame != NULL) {
        if (!old_is_spilled_) {
          frame->SpillAll();
        } else {
          frame->AssertIsSpilled();
        }
      }
      Isolate::Current()->set_is_virtual_frame_in_spilled_scope(true);
    }
    ~SpilledScope() {
      Isolate::Current()->set_is_virtual_frame_in_spilled_scope(
          old_is_spilled_);
    }
    static bool is_spilled() {
      return Isolate::Current()->is_virtual_frame_in_spilled_scope();
    }

   private:
    int old_is_spilled_;

    SpilledScope() {}

    friend class RegisterAllocationScope;
  };

  class RegisterAllocationScope BASE_EMBEDDED {
   public:
    // A utility class to introduce a scope where the virtual frame
    // is not spilled, ie. where register allocation occurs.  Eventually
    // when RegisterAllocationScope is ubiquitous it can be removed
    // along with the (by then unused) SpilledScope class.
    inline explicit RegisterAllocationScope(CodeGenerator* cgen);
    inline ~RegisterAllocationScope();

   private:
    CodeGenerator* cgen_;
    bool old_is_spilled_;

    RegisterAllocationScope() {}
  };

  // An illegal index into the virtual frame.
  static const int kIllegalIndex = -1;

  // Construct an initial virtual frame on entry to a JS function.
  inline VirtualFrame();

  // Construct an invalid virtual frame, used by JumpTargets.
  inline VirtualFrame(InvalidVirtualFrameInitializer* dummy);

  // Construct a virtual frame as a clone of an existing one.
  explicit inline VirtualFrame(VirtualFrame* original);

  inline CodeGenerator* cgen() const;
  inline MacroAssembler* masm();

  // The number of elements on the virtual frame.
  int element_count() const { return element_count_; }

  // The height of the virtual expression stack.
  inline int height() const;

  bool is_used(int num) {
    switch (num) {
      case 0: {  // a0.
        return kA0InUse[top_of_stack_state_];
      }
      case 1: {  // a1.
        return kA1InUse[top_of_stack_state_];
      }
      case 2:
      case 3:
      case 4:
      case 5:
      case 6: {  // a2 to a3, t0 to t2.
        ASSERT(num - kFirstAllocatedRegister < kNumberOfAllocatedRegisters);
        ASSERT(num >= kFirstAllocatedRegister);
        if ((register_allocation_map_ &
             (1 << (num - kFirstAllocatedRegister))) == 0) {
          return false;
        } else {
          return true;
        }
      }
      default: {
        ASSERT(num < kFirstAllocatedRegister ||
               num >= kFirstAllocatedRegister + kNumberOfAllocatedRegisters);
        return false;
      }
    }
  }

  // Add extra in-memory elements to the top of the frame to match an actual
  // frame (eg, the frame after an exception handler is pushed). No code is
  // emitted.
  void Adjust(int count);

  // Forget elements from the top of the frame to match an actual frame (eg,
  // the frame after a runtime call). No code is emitted except to bring the
  // frame to a spilled state.
  void Forget(int count);


  // Spill all values from the frame to memory.
  void SpillAll();

  void AssertIsSpilled() const {
    ASSERT(top_of_stack_state_ == NO_TOS_REGISTERS);
    ASSERT(register_allocation_map_ == 0);
  }

  void AssertIsNotSpilled() {
    ASSERT(!SpilledScope::is_spilled());
  }

  // Spill all occurrences of a specific register from the frame.
  void Spill(Register reg) {
    UNIMPLEMENTED();
  }

  // Spill all occurrences of an arbitrary register if possible. Return the
  // register spilled or no_reg if it was not possible to free any register
  // (ie, they all have frame-external references). Unimplemented.
  Register SpillAnyRegister();

  // Make this virtual frame have a state identical to an expected virtual
  // frame. As a side effect, code may be emitted to make this frame match
  // the expected one.
  void MergeTo(const VirtualFrame* expected,
               Condition cond = al,
               Register r1 = no_reg,
               const Operand& r2 = Operand(no_reg));

  void MergeTo(VirtualFrame* expected,
               Condition cond = al,
               Register r1 = no_reg,
               const Operand& r2 = Operand(no_reg));

  // Checks whether this frame can be branched to by the other frame.
  bool IsCompatibleWith(const VirtualFrame* other) const {
    return (tos_known_smi_map_ & (~other->tos_known_smi_map_)) == 0;
  }

  inline void ForgetTypeInfo() {
    tos_known_smi_map_ = 0;
  }

  // Detach a frame from its code generator, perhaps temporarily. This
  // tells the register allocator that it is free to use frame-internal
  // registers. Used when the code generator's frame is switched from this
  // one to NULL by an unconditional jump.
  void DetachFromCodeGenerator() {
  }

  // (Re)attach a frame to its code generator. This informs the register
  // allocator that the frame-internal register references are active again.
  // Used when a code generator's frame is switched from NULL to this one by
  // binding a label.
  void AttachToCodeGenerator() {
  }

  // Emit code for the physical JS entry and exit frame sequences. After
  // calling Enter, the virtual frame is ready for use; and after calling
  // Exit it should not be used. Note that Enter does not allocate space in
  // the physical frame for storing frame-allocated locals.
  void Enter();
  void Exit();

  // Prepare for returning from the frame by elements in the virtual frame.
  // This avoids generating unnecessary merge code when jumping to the shared
  // return site. No spill code emitted. Value to return should be in v0.
  inline void PrepareForReturn();

  // Number of local variables after when we use a loop for allocating.
  static const int kLocalVarBound = 5;

  // Allocate and initialize the frame-allocated locals.
  void AllocateStackSlots();

  // The current top of the expression stack as an assembly operand.
  MemOperand Top() {
    AssertIsSpilled();
    return MemOperand(sp, 0);
  }

  // An element of the expression stack as an assembly operand.
  MemOperand ElementAt(int index) {
    int adjusted_index = index - kVirtualElements[top_of_stack_state_];
    ASSERT(adjusted_index >= 0);
    return MemOperand(sp, adjusted_index * kPointerSize);
  }

  bool KnownSmiAt(int index) {
    if (index >= kTOSKnownSmiMapSize) return false;
    return (tos_known_smi_map_ & (1 << index)) != 0;
  }
  // A frame-allocated local as an assembly operand.
  inline MemOperand LocalAt(int index);

  // Push the address of the receiver slot on the frame.
  void PushReceiverSlotAddress();

  // The function frame slot.
  MemOperand Function() { return MemOperand(fp, kFunctionOffset); }

  // The context frame slot.
  MemOperand Context() { return MemOperand(fp, kContextOffset); }

  // A parameter as an assembly operand.
  inline MemOperand ParameterAt(int index);

  // The receiver frame slot.
  inline MemOperand Receiver();

  // Push a try-catch or try-finally handler on top of the virtual frame.
  void PushTryHandler(HandlerType type);

  // Call stub given the number of arguments it expects on (and
  // removes from) the stack.
  inline void CallStub(CodeStub* stub, int arg_count);

  // Call JS function from top of the stack with arguments
  // taken from the stack.
  void CallJSFunction(int arg_count);

  // Call runtime given the number of arguments expected on (and
  // removed from) the stack.
  void CallRuntime(const Runtime::Function* f, int arg_count);
  void CallRuntime(Runtime::FunctionId id, int arg_count);

#ifdef ENABLE_DEBUGGER_SUPPORT
  void DebugBreak();
#endif

  // Invoke builtin given the number of arguments it expects on (and
  // removes from) the stack.
  void InvokeBuiltin(Builtins::JavaScript id,
                     InvokeJSFlags flag,
                     int arg_count);

  // Call load IC. Receiver is on the stack and is consumed. Result is returned
  // in v0.
  void CallLoadIC(Handle<String> name, RelocInfo::Mode mode);

  // Call store IC. If the load is contextual, value is found on top of the
  // frame. If not, value and receiver are on the frame. Both are consumed.
  // Result is returned in v0.
  void CallStoreIC(Handle<String> name, bool is_contextual);

  // Call keyed load IC. Key and receiver are on the stack. Both are consumed.
  // Result is returned in v0.
  void CallKeyedLoadIC();

  // Call keyed store IC. Value, key and receiver are on the stack. All three
  // are consumed. Result is returned in v0 (and a0).
  void CallKeyedStoreIC();

  // Call into an IC stub given the number of arguments it removes
  // from the stack. Register arguments to the IC stub are implicit,
  // and depend on the type of IC stub.
  void CallCodeObject(Handle<Code> ic,
                      RelocInfo::Mode rmode,
                      int dropped_args);

  // Drop a number of elements from the top of the expression stack. May
  // emit code to affect the physical frame. Does not clobber any registers
  // excepting possibly the stack pointer.
  void Drop(int count);

  // Drop one element.
  void Drop() { Drop(1); }

  // Pop an element from the top of the expression stack. Discards
  // the result.
  void Pop();

  // Pop an element from the top of the expression stack.  The register
  // will be one normally used for the top of stack register allocation
  // so you can't hold on to it if you push on the stack.
  Register PopToRegister(Register but_not_to_this_one = no_reg);

  // Look at the top of the stack.  The register returned is aliased and
  // must be copied to a scratch register before modification.
  Register Peek();

  // Look at the value beneath the top of the stack. The register returned is
  // aliased and must be copied to a scratch register before modification.
  Register Peek2();

  // Duplicate the top of stack.
  void Dup();

  // Duplicate the two elements on top of stack.
  void Dup2();

  // Flushes all registers, but it puts a copy of the top-of-stack in a0.
  void SpillAllButCopyTOSToA0();

  // Flushes all registers, but it puts a copy of the top-of-stack in a1.
  void SpillAllButCopyTOSToA1();

  // Flushes all registers, but it puts a copy of the top-of-stack in a1
  // and the next value on the stack in a0.
  void SpillAllButCopyTOSToA1A0();

  // Pop and save an element from the top of the expression stack and
  // emit a corresponding pop instruction.
  void EmitPop(Register reg);
  // Same but for multiple registers
  void EmitMultiPop(RegList regs);
  void EmitMultiPopReversed(RegList regs);


  // Takes the top two elements and puts them in a0 (top element) and a1
  // (second element).
  void PopToA1A0();

  // Takes the top element and puts it in a1.
  void PopToA1();

  // Takes the top element and puts it in a0.
  void PopToA0();

  // Push an element on top of the expression stack and emit a
  // corresponding push instruction.
  void EmitPush(Register reg, TypeInfo type_info = TypeInfo::Unknown());
  void EmitPush(Operand operand, TypeInfo type_info = TypeInfo::Unknown());
  void EmitPush(MemOperand operand, TypeInfo type_info = TypeInfo::Unknown());
  void EmitPushRoot(Heap::RootListIndex index);

  // Overwrite the nth thing on the stack.  If the nth position is in a
  // register then this turns into a Move, otherwise an sw.  Afterwards
  // you can still use the register even if it is a register that can be
  // used for TOS (a0 or a1).
  void SetElementAt(Register reg, int this_far_down);

  // Get a register which is free and which must be immediately used to
  // push on the top of the stack.
  Register GetTOSRegister();

  // Same but for multiple registers.
  void EmitMultiPush(RegList regs);
  void EmitMultiPushReversed(RegList regs);

  static Register scratch0() { return t4; }
  static Register scratch1() { return t5; }
  static Register scratch2() { return t6; }

 private:
  static const int kLocal0Offset = JavaScriptFrameConstants::kLocal0Offset;
  static const int kFunctionOffset = JavaScriptFrameConstants::kFunctionOffset;
  static const int kContextOffset = StandardFrameConstants::kContextOffset;

  static const int kHandlerSize = StackHandlerConstants::kSize / kPointerSize;
  static const int kPreallocatedElements = 5 + 8;  // 8 expression stack slots.

  // 5 states for the top of stack, which can be in memory or in a0 and a1.
  enum TopOfStack { NO_TOS_REGISTERS, A0_TOS, A1_TOS, A1_A0_TOS, A0_A1_TOS,
                    TOS_STATES};
  static const int kMaxTOSRegisters = 2;

  static const bool kA0InUse[TOS_STATES];
  static const bool kA1InUse[TOS_STATES];
  static const int kVirtualElements[TOS_STATES];
  static const TopOfStack kStateAfterPop[TOS_STATES];
  static const TopOfStack kStateAfterPush[TOS_STATES];
  static const Register kTopRegister[TOS_STATES];
  static const Register kBottomRegister[TOS_STATES];

  // We allocate up to 5 locals in registers.
  static const int kNumberOfAllocatedRegisters = 5;
  // r2 to r6 are allocated to locals.
  static const int kFirstAllocatedRegister = 2;

  static const Register kAllocatedRegisters[kNumberOfAllocatedRegisters];

  static Register AllocatedRegister(int r) {
    ASSERT(r >= 0 && r < kNumberOfAllocatedRegisters);
    return kAllocatedRegisters[r];
  }

  // The number of elements on the stack frame.
  int element_count_;
  TopOfStack top_of_stack_state_:3;
  int register_allocation_map_:kNumberOfAllocatedRegisters;
  static const int kTOSKnownSmiMapSize = 4;
  unsigned tos_known_smi_map_:kTOSKnownSmiMapSize;

  // The index of the element that is at the processor's stack pointer
  // (the sp register).  For now since everything is in memory it is given
  // by the number of elements on the not-very-virtual stack frame.
  int stack_pointer() { return element_count_ - 1; }

  // The number of frame-allocated locals and parameters respectively.
  inline int parameter_count() const;
  inline int local_count() const;

  // The index of the element that is at the processor's frame pointer
  // (the fp register). The parameters, receiver, function, and context
  // are below the frame pointer.
  inline int frame_pointer() const;

  // The index of the first parameter. The receiver lies below the first
  // parameter.
  int param0_index() { return 1; }

  // The index of the context slot in the frame. It is immediately
  // below the frame pointer.
  inline int context_index();

  // The index of the function slot in the frame. It is below the frame
  // pointer and context slot.
  inline int function_index();

  // The index of the first local. Between the frame pointer and the
  // locals lies the return address.
  inline int local0_index() const;

  // The index of the base of the expression stack.
  inline int expression_base_index() const;

  // Convert a frame index into a frame pointer relative offset into the
  // actual stack.
  inline int fp_relative(int index);

  // Spill all elements in registers. Spill the top spilled_args elements
  // on the frame. Sync all other frame elements.
  // Then drop dropped_args elements from the virtual frame, to match
  // the effect of an upcoming call that will drop them from the stack.
  void PrepareForCall(int spilled_args, int dropped_args);

  // If all top-of-stack registers are in use then the lowest one is pushed
  // onto the physical stack and made free.
  void EnsureOneFreeTOSRegister();

  // Emit instructions to get the top of stack state from where we are to where
  // we want to be.
  void MergeTOSTo(TopOfStack expected_state,
                  Condition cond = al,
                  Register r1 = no_reg,
                  const Operand& r2 = Operand(no_reg));

  inline bool Equals(const VirtualFrame* other);

  inline void LowerHeight(int count) {
    element_count_ -= count;
    if (count >= kTOSKnownSmiMapSize) {
      tos_known_smi_map_ = 0;
    } else {
      tos_known_smi_map_ >>= count;
    }
  }

  inline void RaiseHeight(int count, unsigned known_smi_map = 0) {
    ASSERT(known_smi_map < (1u << count));
    element_count_ += count;
    if (count >= kTOSKnownSmiMapSize) {
      tos_known_smi_map_ = known_smi_map;
    } else {
      tos_known_smi_map_ = ((tos_known_smi_map_ << count) | known_smi_map);
    }
  }
  friend class JumpTarget;
};


} }  // namespace v8::internal

#endif  // V8_MIPS_VIRTUAL_FRAME_MIPS_H_