diff options
Diffstat (limited to 'deps/v8/src/compiler/backend/frame-elider.cc')
-rw-r--r-- | deps/v8/src/compiler/backend/frame-elider.cc | 158 |
1 files changed, 158 insertions, 0 deletions
diff --git a/deps/v8/src/compiler/backend/frame-elider.cc b/deps/v8/src/compiler/backend/frame-elider.cc new file mode 100644 index 0000000000..2167d0abaa --- /dev/null +++ b/deps/v8/src/compiler/backend/frame-elider.cc @@ -0,0 +1,158 @@ +// 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 |