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// Copyright 2015 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.
#include "src/compiler/backend/frame-elider.h"
#include "src/base/adapters.h"
namespace v8 {
namespace internal {
namespace compiler {
FrameElider::FrameElider(InstructionSequence* code) : code_(code) {}
void FrameElider::Run() {
MarkBlocks();
PropagateMarks();
MarkDeConstruction();
}
void FrameElider::MarkBlocks() {
for (InstructionBlock* block : instruction_blocks()) {
if (block->needs_frame()) continue;
for (int i = block->code_start(); i < block->code_end(); ++i) {
const Instruction* instr = InstructionAt(i);
if (instr->IsCall() || instr->IsDeoptimizeCall() ||
instr->arch_opcode() == ArchOpcode::kArchStackPointer ||
instr->arch_opcode() == ArchOpcode::kArchFramePointer) {
block->mark_needs_frame();
break;
}
}
}
}
void FrameElider::PropagateMarks() {
while (PropagateInOrder() || PropagateReversed()) {
}
}
void FrameElider::MarkDeConstruction() {
for (InstructionBlock* block : instruction_blocks()) {
if (block->needs_frame()) {
// Special case: The start block needs a frame.
if (block->predecessors().empty()) {
block->mark_must_construct_frame();
}
// Find "frame -> no frame" transitions, inserting frame
// deconstructions.
for (RpoNumber& succ : block->successors()) {
if (!InstructionBlockAt(succ)->needs_frame()) {
DCHECK_EQ(1U, block->SuccessorCount());
const Instruction* last =
InstructionAt(block->last_instruction_index());
if (last->IsThrow() || last->IsTailCall() ||
last->IsDeoptimizeCall()) {
// We need to keep the frame if we exit the block through any
// of these.
continue;
}
// The only cases when we need to deconstruct are ret and jump.
DCHECK(last->IsRet() || last->IsJump());
block->mark_must_deconstruct_frame();
}
}
} else {
// Find "no frame -> frame" transitions, inserting frame constructions.
for (RpoNumber& succ : block->successors()) {
if (InstructionBlockAt(succ)->needs_frame()) {
DCHECK_NE(1U, block->SuccessorCount());
InstructionBlockAt(succ)->mark_must_construct_frame();
}
}
}
}
}
bool FrameElider::PropagateInOrder() {
bool changed = false;
for (InstructionBlock* block : instruction_blocks()) {
changed |= PropagateIntoBlock(block);
}
return changed;
}
bool FrameElider::PropagateReversed() {
bool changed = false;
for (InstructionBlock* block : base::Reversed(instruction_blocks())) {
changed |= PropagateIntoBlock(block);
}
return changed;
}
bool FrameElider::PropagateIntoBlock(InstructionBlock* block) {
// Already marked, nothing to do...
if (block->needs_frame()) return false;
// Never mark the dummy end node, otherwise we might incorrectly decide to
// put frame deconstruction code there later,
if (block->successors().empty()) return false;
// Propagate towards the end ("downwards") if there is a predecessor needing
// a frame, but don't "bleed" from deferred code to non-deferred code.
for (RpoNumber& pred : block->predecessors()) {
if (InstructionBlockAt(pred)->needs_frame() &&
(!InstructionBlockAt(pred)->IsDeferred() || block->IsDeferred())) {
block->mark_needs_frame();
return true;
}
}
// Propagate towards start ("upwards")
bool need_frame_successors = false;
if (block->SuccessorCount() == 1) {
// For single successors, propagate the needs_frame information.
need_frame_successors =
InstructionBlockAt(block->successors()[0])->needs_frame();
} else {
// For multiple successors, each successor must only have a single
// predecessor (because the graph is in edge-split form), so each successor
// can independently create/dismantle a frame if needed. Given this
// independent control, only propagate needs_frame if all non-deferred
// blocks need a frame.
for (RpoNumber& succ : block->successors()) {
InstructionBlock* successor_block = InstructionBlockAt(succ);
DCHECK_EQ(1, successor_block->PredecessorCount());
if (!successor_block->IsDeferred()) {
if (successor_block->needs_frame()) {
need_frame_successors = true;
} else {
return false;
}
}
}
}
if (need_frame_successors) {
block->mark_needs_frame();
return true;
} else {
return false;
}
}
const InstructionBlocks& FrameElider::instruction_blocks() const {
return code_->instruction_blocks();
}
InstructionBlock* FrameElider::InstructionBlockAt(RpoNumber rpo_number) const {
return code_->InstructionBlockAt(rpo_number);
}
Instruction* FrameElider::InstructionAt(int index) const {
return code_->InstructionAt(index);
}
} // namespace compiler
} // namespace internal
} // namespace v8
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