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// Copyright 2014 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.
#ifndef V8_COMPILER_FRAME_H_
#define V8_COMPILER_FRAME_H_
#include "src/execution/frame-constants.h"
#include "src/utils/bit-vector.h"
namespace v8 {
namespace internal {
namespace compiler {
class CallDescriptor;
// Collects the spill slot and other frame slot requirements for a compiled
// function. Frames are usually populated by the register allocator and are used
// by Linkage to generate code for the prologue and epilogue to compiled
// code. Frame objects must be considered immutable once they've been
// instantiated and the basic information about the frame has been collected
// into them. Mutable state associated with the frame is stored separately in
// FrameAccessState.
//
// Frames are divided up into four regions.
// - The first is the fixed header, which always has a constant size and can be
// predicted before code generation begins depending on the type of code being
// generated.
// - The second is the region for spill slots, which is immediately below the
// fixed header and grows as the register allocator needs to spill to the
// stack and asks the frame for more space.
// - The third region, which contains the callee-saved registers must be
// reserved after register allocation, since its size can only be precisely
// determined after register allocation once the number of used callee-saved
// register is certain.
// - The fourth region is a scratch area for return values from other functions
// called, if multiple returns cannot all be passed in registers. This region
// Must be last in a stack frame, so that it is positioned immediately below
// the stack frame of a callee to store to.
//
// The frame region immediately below the fixed header contains spill slots
// starting at slot 4 for JSFunctions. The callee-saved frame region below that
// starts at 4+spill_slot_count_. Callee stack slots correspond to
// parameters that are accessible through negative slot ids.
//
// Every slot of a caller or callee frame is accessible by the register
// allocator and gap resolver with a SpillSlotOperand containing its
// corresponding slot id.
//
// Below an example JSFunction Frame with slot ids, frame regions and contents:
//
// slot JS frame
// +-----------------+--------------------------------
// -n-1 | parameter 0 | ^
// |- - - - - - - - -| |
// -n | | Caller
// ... | ... | frame slots
// -2 | parameter n-1 | (slot < 0)
// |- - - - - - - - -| |
// -1 | parameter n | v
// -----+-----------------+--------------------------------
// 0 | return addr | ^ ^
// |- - - - - - - - -| | |
// 1 | saved frame ptr | Fixed |
// |- - - - - - - - -| Header <-- frame ptr |
// 2 |Context/Frm. Type| | |
// |- - - - - - - - -| | |
// 3 | [JSFunction] | v |
// +-----------------+---- |
// 4 | spill 1 | ^ Callee
// |- - - - - - - - -| | frame slots
// ... | ... | Spill slots (slot >= 0)
// |- - - - - - - - -| | |
// m+3 | spill m | v |
// +-----------------+---- |
// m+4 | callee-saved 1 | ^ |
// |- - - - - - - - -| | |
// | ... | Callee-saved |
// |- - - - - - - - -| | |
// m+r+3 | callee-saved r | v |
// +-----------------+---- |
// m+r+4 | return 0 | ^ |
// |- - - - - - - - -| | |
// | ... | Return |
// |- - - - - - - - -| | |
// | return q-1 | v v
// -----+-----------------+----- <-- stack ptr -------------
//
class V8_EXPORT_PRIVATE Frame : public ZoneObject {
public:
explicit Frame(int fixed_frame_size_in_slots);
Frame(const Frame&) = delete;
Frame& operator=(const Frame&) = delete;
inline int GetTotalFrameSlotCount() const { return frame_slot_count_; }
inline int GetFixedSlotCount() const { return fixed_slot_count_; }
inline int GetSpillSlotCount() const { return spill_slot_count_; }
inline int GetReturnSlotCount() const { return return_slot_count_; }
void SetAllocatedRegisters(BitVector* regs) {
DCHECK_NULL(allocated_registers_);
allocated_registers_ = regs;
}
void SetAllocatedDoubleRegisters(BitVector* regs) {
DCHECK_NULL(allocated_double_registers_);
allocated_double_registers_ = regs;
}
bool DidAllocateDoubleRegisters() const {
return !allocated_double_registers_->IsEmpty();
}
void AlignSavedCalleeRegisterSlots(int alignment = kDoubleSize) {
int alignment_slots = alignment / kSystemPointerSize;
int delta = alignment_slots - (frame_slot_count_ & (alignment_slots - 1));
if (delta != alignment_slots) {
frame_slot_count_ += delta;
}
spill_slot_count_ += delta;
}
void AllocateSavedCalleeRegisterSlots(int count) {
frame_slot_count_ += count;
}
int AllocateSpillSlot(int width, int alignment = 0) {
DCHECK_EQ(frame_slot_count_,
fixed_slot_count_ + spill_slot_count_ + return_slot_count_);
int frame_slot_count_before = frame_slot_count_;
if (alignment > kSystemPointerSize) {
// Slots are pointer sized, so alignment greater than a pointer size
// requires allocating additional slots.
width += alignment - kSystemPointerSize;
}
AllocateAlignedFrameSlots(width);
spill_slot_count_ += frame_slot_count_ - frame_slot_count_before;
return frame_slot_count_ - return_slot_count_ - 1;
}
void EnsureReturnSlots(int count) {
if (count > return_slot_count_) {
count -= return_slot_count_;
frame_slot_count_ += count;
return_slot_count_ += count;
}
}
int AlignFrame(int alignment = kDoubleSize);
int ReserveSpillSlots(size_t slot_count) {
DCHECK_EQ(0, spill_slot_count_);
spill_slot_count_ += static_cast<int>(slot_count);
frame_slot_count_ += static_cast<int>(slot_count);
return frame_slot_count_ - 1;
}
private:
void AllocateAlignedFrameSlots(int width) {
DCHECK_LT(0, width);
int new_frame_slots = (width + kSystemPointerSize - 1) / kSystemPointerSize;
// Align to 8 bytes if width is a multiple of 8 bytes, and to 16 bytes if
// multiple of 16.
int align_to =
(width & 15) == 0 ? 16 : (width & 7) == 0 ? 8 : kSystemPointerSize;
frame_slot_count_ = RoundUp(frame_slot_count_ + new_frame_slots,
align_to / kSystemPointerSize);
DCHECK_LT(0, frame_slot_count_);
}
private:
int fixed_slot_count_;
int frame_slot_count_;
int spill_slot_count_;
int return_slot_count_;
BitVector* allocated_registers_;
BitVector* allocated_double_registers_;
};
// Represents an offset from either the stack pointer or frame pointer.
class FrameOffset {
public:
inline bool from_stack_pointer() { return (offset_ & 1) == kFromSp; }
inline bool from_frame_pointer() { return (offset_ & 1) == kFromFp; }
inline int offset() { return offset_ & ~1; }
inline static FrameOffset FromStackPointer(int offset) {
DCHECK_EQ(0, offset & 1);
return FrameOffset(offset | kFromSp);
}
inline static FrameOffset FromFramePointer(int offset) {
DCHECK_EQ(0, offset & 1);
return FrameOffset(offset | kFromFp);
}
private:
explicit FrameOffset(int offset) : offset_(offset) {}
int offset_; // Encodes SP or FP in the low order bit.
static const int kFromSp = 1;
static const int kFromFp = 0;
};
// Encapsulates the mutable state maintained during code generation about the
// current function's frame.
class FrameAccessState : public ZoneObject {
public:
explicit FrameAccessState(const Frame* const frame)
: frame_(frame),
access_frame_with_fp_(false),
sp_delta_(0),
has_frame_(false) {}
const Frame* frame() const { return frame_; }
V8_EXPORT_PRIVATE void MarkHasFrame(bool state);
int sp_delta() const { return sp_delta_; }
void ClearSPDelta() { sp_delta_ = 0; }
void IncreaseSPDelta(int amount) { sp_delta_ += amount; }
bool access_frame_with_fp() const { return access_frame_with_fp_; }
// Regardless of how we access slots on the stack - using sp or fp - do we
// have a frame, at the current stage in code generation.
bool has_frame() const { return has_frame_; }
void SetFrameAccessToDefault();
void SetFrameAccessToFP() { access_frame_with_fp_ = true; }
void SetFrameAccessToSP() { access_frame_with_fp_ = false; }
int GetSPToFPSlotCount() const {
int frame_slot_count =
(has_frame() ? frame()->GetTotalFrameSlotCount() : kElidedFrameSlots) -
StandardFrameConstants::kFixedSlotCountAboveFp;
return frame_slot_count + sp_delta();
}
int GetSPToFPOffset() const {
return GetSPToFPSlotCount() * kSystemPointerSize;
}
// Get the frame offset for a given spill slot. The location depends on the
// calling convention and the specific frame layout, and may thus be
// architecture-specific. Negative spill slots indicate arguments on the
// caller's frame.
FrameOffset GetFrameOffset(int spill_slot) const;
private:
const Frame* const frame_;
bool access_frame_with_fp_;
int sp_delta_;
bool has_frame_;
};
} // namespace compiler
} // namespace internal
} // namespace v8
#endif // V8_COMPILER_FRAME_H_