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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.
#include "src/compiler/move-optimizer.h"
namespace v8 {
namespace internal {
namespace compiler {
namespace {
MoveOperands* PrepareInsertAfter(ParallelMove* left, MoveOperands* move,
Zone* zone) {
auto move_ops = left->move_operands();
MoveOperands* replacement = nullptr;
MoveOperands* to_eliminate = nullptr;
for (auto curr = move_ops->begin(); curr != move_ops->end(); ++curr) {
if (curr->IsEliminated()) continue;
if (curr->destination()->Equals(move->source())) {
DCHECK(!replacement);
replacement = curr;
if (to_eliminate != nullptr) break;
} else if (curr->destination()->Equals(move->destination())) {
DCHECK(!to_eliminate);
to_eliminate = curr;
if (replacement != nullptr) break;
}
}
DCHECK(!(replacement == to_eliminate && replacement != nullptr));
if (replacement != nullptr) {
auto new_source = InstructionOperand::New(
zone, replacement->source()->kind(), replacement->source()->index());
move->set_source(new_source);
}
return to_eliminate;
}
bool GapsCanMoveOver(Instruction* instr) {
DCHECK(!instr->IsGapMoves());
return instr->IsSourcePosition() || instr->IsNop();
}
int FindFirstNonEmptySlot(GapInstruction* gap) {
int i = GapInstruction::FIRST_INNER_POSITION;
for (; i <= GapInstruction::LAST_INNER_POSITION; i++) {
auto move = gap->parallel_moves()[i];
if (move == nullptr) continue;
auto move_ops = move->move_operands();
auto op = move_ops->begin();
for (; op != move_ops->end(); ++op) {
if (!op->IsRedundant()) break;
op->Eliminate();
}
if (op != move_ops->end()) break; // Found non-redundant move.
move_ops->Rewind(0); // Clear this redundant move.
}
return i;
}
} // namepace
MoveOptimizer::MoveOptimizer(Zone* local_zone, InstructionSequence* code)
: local_zone_(local_zone),
code_(code),
to_finalize_(local_zone),
temp_vector_0_(local_zone),
temp_vector_1_(local_zone) {}
void MoveOptimizer::Run() {
for (auto* block : code()->instruction_blocks()) {
CompressBlock(block);
}
for (auto gap : to_finalize_) {
FinalizeMoves(gap);
}
}
void MoveOptimizer::CompressMoves(MoveOpVector* eliminated, ParallelMove* left,
ParallelMove* right) {
DCHECK(eliminated->empty());
auto move_ops = right->move_operands();
if (!left->move_operands()->is_empty()) {
// Modify the right moves in place and collect moves that will be killed by
// merging the two gaps.
for (auto op = move_ops->begin(); op != move_ops->end(); ++op) {
if (op->IsRedundant()) continue;
MoveOperands* to_eliminate = PrepareInsertAfter(left, op, code_zone());
if (to_eliminate != nullptr) eliminated->push_back(to_eliminate);
}
// Eliminate dead moves. Must happen before insertion of new moves as the
// contents of eliminated are pointers into a list.
for (auto to_eliminate : *eliminated) {
to_eliminate->Eliminate();
}
eliminated->clear();
}
// Add all possibly modified moves from right side.
for (auto op = move_ops->begin(); op != move_ops->end(); ++op) {
if (op->IsRedundant()) continue;
left->move_operands()->Add(*op, code_zone());
}
// Nuke right.
move_ops->Rewind(0);
}
// Smash all consecutive moves into the left most move slot and accumulate them
// as much as possible across instructions.
void MoveOptimizer::CompressBlock(InstructionBlock* block) {
auto temp_vector = temp_vector_0();
DCHECK(temp_vector.empty());
GapInstruction* prev_gap = nullptr;
for (int index = block->code_start(); index < block->code_end(); ++index) {
auto instr = code()->instructions()[index];
if (!instr->IsGapMoves()) {
if (GapsCanMoveOver(instr)) continue;
if (prev_gap != nullptr) to_finalize_.push_back(prev_gap);
prev_gap = nullptr;
continue;
}
auto gap = GapInstruction::cast(instr);
int i = FindFirstNonEmptySlot(gap);
// Nothing to do here.
if (i == GapInstruction::LAST_INNER_POSITION + 1) {
if (prev_gap != nullptr) {
// Slide prev_gap down so we always know where to look for it.
std::swap(prev_gap->parallel_moves()[0], gap->parallel_moves()[0]);
prev_gap = gap;
}
continue;
}
// Move the first non-empty gap to position 0.
std::swap(gap->parallel_moves()[0], gap->parallel_moves()[i]);
auto left = gap->parallel_moves()[0];
// Compress everything into position 0.
for (++i; i <= GapInstruction::LAST_INNER_POSITION; ++i) {
auto move = gap->parallel_moves()[i];
if (move == nullptr) continue;
CompressMoves(&temp_vector, left, move);
}
if (prev_gap != nullptr) {
// Smash left into prev_gap, killing left.
auto pred_moves = prev_gap->parallel_moves()[0];
CompressMoves(&temp_vector, pred_moves, left);
// Slide prev_gap down so we always know where to look for it.
std::swap(prev_gap->parallel_moves()[0], gap->parallel_moves()[0]);
}
prev_gap = gap;
}
if (prev_gap != nullptr) to_finalize_.push_back(prev_gap);
}
// Split multiple loads of the same constant or stack slot off into the second
// slot and keep remaining moves in the first slot.
void MoveOptimizer::FinalizeMoves(GapInstruction* gap) {
auto loads = temp_vector_0();
DCHECK(loads.empty());
auto new_moves = temp_vector_1();
DCHECK(new_moves.empty());
auto move_ops = gap->parallel_moves()[0]->move_operands();
for (auto move = move_ops->begin(); move != move_ops->end(); ++move) {
if (move->IsRedundant()) {
move->Eliminate();
continue;
}
if (!(move->source()->IsConstant() || move->source()->IsStackSlot() ||
move->source()->IsDoubleStackSlot()))
continue;
// Search for existing move to this slot.
MoveOperands* found = nullptr;
for (auto load : loads) {
if (load->source()->Equals(move->source())) {
found = load;
break;
}
}
// Not found so insert.
if (found == nullptr) {
loads.push_back(move);
// Replace source with copy for later use.
auto dest = move->destination();
move->set_destination(
InstructionOperand::New(code_zone(), dest->kind(), dest->index()));
continue;
}
if ((found->destination()->IsStackSlot() ||
found->destination()->IsDoubleStackSlot()) &&
!(move->destination()->IsStackSlot() ||
move->destination()->IsDoubleStackSlot())) {
// Found a better source for this load. Smash it in place to affect other
// loads that have already been split.
InstructionOperand::Kind found_kind = found->destination()->kind();
int found_index = found->destination()->index();
auto next_dest =
InstructionOperand::New(code_zone(), found_kind, found_index);
auto dest = move->destination();
found->destination()->ConvertTo(dest->kind(), dest->index());
move->set_destination(next_dest);
}
// move from load destination.
move->set_source(found->destination());
new_moves.push_back(move);
}
loads.clear();
if (new_moves.empty()) return;
// Insert all new moves into slot 1.
auto slot_1 = gap->GetOrCreateParallelMove(
static_cast<GapInstruction::InnerPosition>(1), code_zone());
DCHECK(slot_1->move_operands()->is_empty());
slot_1->move_operands()->AddBlock(MoveOperands(nullptr, nullptr),
static_cast<int>(new_moves.size()),
code_zone());
auto it = slot_1->move_operands()->begin();
for (auto new_move : new_moves) {
std::swap(*new_move, *it);
++it;
}
DCHECK_EQ(it, slot_1->move_operands()->end());
new_moves.clear();
}
} // namespace compiler
} // namespace internal
} // namespace v8
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