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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 {
struct MoveKey {
InstructionOperand source;
InstructionOperand destination;
};
struct MoveKeyCompare {
bool operator()(const MoveKey& a, const MoveKey& b) const {
if (a.source.EqualsCanonicalized(b.source)) {
return a.destination.CompareCanonicalized(b.destination);
}
return a.source.CompareCanonicalized(b.source);
}
};
typedef ZoneMap<MoveKey, unsigned, MoveKeyCompare> MoveMap;
class OperandSet {
public:
explicit OperandSet(ZoneVector<InstructionOperand>* buffer)
: set_(buffer), fp_reps_(0) {
buffer->clear();
}
void InsertOp(const InstructionOperand& op) {
set_->push_back(op);
if (!kSimpleFPAliasing && op.IsFPRegister())
fp_reps_ |= RepBit(LocationOperand::cast(op).representation());
}
bool Contains(const InstructionOperand& op) const {
for (const InstructionOperand& elem : *set_) {
if (elem.EqualsCanonicalized(op)) return true;
}
return false;
}
bool ContainsOpOrAlias(const InstructionOperand& op) const {
if (Contains(op)) return true;
if (!kSimpleFPAliasing && op.IsFPRegister()) {
// Platforms where FP registers have complex aliasing need extra checks.
const LocationOperand& loc = LocationOperand::cast(op);
MachineRepresentation rep = loc.representation();
// If haven't encountered mixed rep FP registers, skip the extra checks.
if (!HasMixedFPReps(fp_reps_ | RepBit(rep))) return false;
// Check register against aliasing registers of other FP representations.
MachineRepresentation other_rep1, other_rep2;
switch (rep) {
case MachineRepresentation::kFloat32:
other_rep1 = MachineRepresentation::kFloat64;
other_rep2 = MachineRepresentation::kSimd128;
break;
case MachineRepresentation::kFloat64:
other_rep1 = MachineRepresentation::kFloat32;
other_rep2 = MachineRepresentation::kSimd128;
break;
case MachineRepresentation::kSimd128:
other_rep1 = MachineRepresentation::kFloat32;
other_rep2 = MachineRepresentation::kFloat64;
break;
default:
UNREACHABLE();
break;
}
const RegisterConfiguration* config = RegisterConfiguration::Default();
int base = -1;
int aliases =
config->GetAliases(rep, loc.register_code(), other_rep1, &base);
DCHECK(aliases > 0 || (aliases == 0 && base == -1));
while (aliases--) {
if (Contains(AllocatedOperand(LocationOperand::REGISTER, other_rep1,
base + aliases))) {
return true;
}
}
aliases = config->GetAliases(rep, loc.register_code(), other_rep2, &base);
DCHECK(aliases > 0 || (aliases == 0 && base == -1));
while (aliases--) {
if (Contains(AllocatedOperand(LocationOperand::REGISTER, other_rep2,
base + aliases))) {
return true;
}
}
}
return false;
}
private:
static int RepBit(MachineRepresentation rep) {
return 1 << static_cast<int>(rep);
}
static bool HasMixedFPReps(int reps) {
return reps && !base::bits::IsPowerOfTwo(reps);
}
ZoneVector<InstructionOperand>* set_;
int fp_reps_;
};
int FindFirstNonEmptySlot(const Instruction* instr) {
int i = Instruction::FIRST_GAP_POSITION;
for (; i <= Instruction::LAST_GAP_POSITION; i++) {
ParallelMove* moves = instr->parallel_moves()[i];
if (moves == nullptr) continue;
for (MoveOperands* move : *moves) {
if (!move->IsRedundant()) return i;
move->Eliminate();
}
moves->clear(); // Clear this redundant move.
}
return i;
}
} // namespace
MoveOptimizer::MoveOptimizer(Zone* local_zone, InstructionSequence* code)
: local_zone_(local_zone),
code_(code),
local_vector_(local_zone),
operand_buffer1(local_zone),
operand_buffer2(local_zone) {}
void MoveOptimizer::Run() {
for (Instruction* instruction : code()->instructions()) {
CompressGaps(instruction);
}
for (InstructionBlock* block : code()->instruction_blocks()) {
CompressBlock(block);
}
for (InstructionBlock* block : code()->instruction_blocks()) {
if (block->PredecessorCount() <= 1) continue;
if (!block->IsDeferred()) {
bool has_only_deferred = true;
for (RpoNumber& pred_id : block->predecessors()) {
if (!code()->InstructionBlockAt(pred_id)->IsDeferred()) {
has_only_deferred = false;
break;
}
}
// This would pull down common moves. If the moves occur in deferred
// blocks, and the closest common successor is not deferred, we lose the
// optimization of just spilling/filling in deferred blocks, when the
// current block is not deferred.
if (has_only_deferred) continue;
}
OptimizeMerge(block);
}
for (Instruction* gap : code()->instructions()) {
FinalizeMoves(gap);
}
}
void MoveOptimizer::RemoveClobberedDestinations(Instruction* instruction) {
if (instruction->IsCall()) return;
ParallelMove* moves = instruction->parallel_moves()[0];
if (moves == nullptr) return;
DCHECK(instruction->parallel_moves()[1] == nullptr ||
instruction->parallel_moves()[1]->empty());
OperandSet outputs(&operand_buffer1);
OperandSet inputs(&operand_buffer2);
// Outputs and temps are treated together as potentially clobbering a
// destination operand.
for (size_t i = 0; i < instruction->OutputCount(); ++i) {
outputs.InsertOp(*instruction->OutputAt(i));
}
for (size_t i = 0; i < instruction->TempCount(); ++i) {
outputs.InsertOp(*instruction->TempAt(i));
}
// Input operands block elisions.
for (size_t i = 0; i < instruction->InputCount(); ++i) {
inputs.InsertOp(*instruction->InputAt(i));
}
// Elide moves made redundant by the instruction.
for (MoveOperands* move : *moves) {
if (outputs.ContainsOpOrAlias(move->destination()) &&
!inputs.ContainsOpOrAlias(move->destination())) {
move->Eliminate();
}
}
// The ret instruction makes any assignment before it unnecessary, except for
// the one for its input.
if (instruction->IsRet() || instruction->IsTailCall()) {
for (MoveOperands* move : *moves) {
if (!inputs.ContainsOpOrAlias(move->destination())) {
move->Eliminate();
}
}
}
}
void MoveOptimizer::MigrateMoves(Instruction* to, Instruction* from) {
if (from->IsCall()) return;
ParallelMove* from_moves = from->parallel_moves()[0];
if (from_moves == nullptr || from_moves->empty()) return;
OperandSet dst_cant_be(&operand_buffer1);
OperandSet src_cant_be(&operand_buffer2);
// If an operand is an input to the instruction, we cannot move assignments
// where it appears on the LHS.
for (size_t i = 0; i < from->InputCount(); ++i) {
dst_cant_be.InsertOp(*from->InputAt(i));
}
// If an operand is output to the instruction, we cannot move assignments
// where it appears on the RHS, because we would lose its value before the
// instruction.
// Same for temp operands.
// The output can't appear on the LHS because we performed
// RemoveClobberedDestinations for the "from" instruction.
for (size_t i = 0; i < from->OutputCount(); ++i) {
src_cant_be.InsertOp(*from->OutputAt(i));
}
for (size_t i = 0; i < from->TempCount(); ++i) {
src_cant_be.InsertOp(*from->TempAt(i));
}
for (MoveOperands* move : *from_moves) {
if (move->IsRedundant()) continue;
// Assume dest has a value "V". If we have a "dest = y" move, then we can't
// move "z = dest", because z would become y rather than "V".
// We assume CompressMoves has happened before this, which means we don't
// have more than one assignment to dest.
src_cant_be.InsertOp(move->destination());
}
ZoneSet<MoveKey, MoveKeyCompare> move_candidates(local_zone());
// We start with all the moves that don't have conflicting source or
// destination operands are eligible for being moved down.
for (MoveOperands* move : *from_moves) {
if (move->IsRedundant()) continue;
if (!dst_cant_be.ContainsOpOrAlias(move->destination())) {
MoveKey key = {move->source(), move->destination()};
move_candidates.insert(key);
}
}
if (move_candidates.empty()) return;
// Stabilize the candidate set.
bool changed = false;
do {
changed = false;
for (auto iter = move_candidates.begin(); iter != move_candidates.end();) {
auto current = iter;
++iter;
InstructionOperand src = current->source;
if (src_cant_be.ContainsOpOrAlias(src)) {
src_cant_be.InsertOp(current->destination);
move_candidates.erase(current);
changed = true;
}
}
} while (changed);
ParallelMove to_move(local_zone());
for (MoveOperands* move : *from_moves) {
if (move->IsRedundant()) continue;
MoveKey key = {move->source(), move->destination()};
if (move_candidates.find(key) != move_candidates.end()) {
to_move.AddMove(move->source(), move->destination(), code_zone());
move->Eliminate();
}
}
if (to_move.empty()) return;
ParallelMove* dest =
to->GetOrCreateParallelMove(Instruction::GapPosition::START, code_zone());
CompressMoves(&to_move, dest);
DCHECK(dest->empty());
for (MoveOperands* m : to_move) {
dest->push_back(m);
}
}
void MoveOptimizer::CompressMoves(ParallelMove* left, MoveOpVector* right) {
if (right == nullptr) return;
MoveOpVector& eliminated = local_vector();
DCHECK(eliminated.empty());
if (!left->empty()) {
// Modify the right moves in place and collect moves that will be killed by
// merging the two gaps.
for (MoveOperands* move : *right) {
if (move->IsRedundant()) continue;
left->PrepareInsertAfter(move, &eliminated);
}
// Eliminate dead moves.
for (MoveOperands* to_eliminate : eliminated) {
to_eliminate->Eliminate();
}
eliminated.clear();
}
// Add all possibly modified moves from right side.
for (MoveOperands* move : *right) {
if (move->IsRedundant()) continue;
left->push_back(move);
}
// Nuke right.
right->clear();
DCHECK(eliminated.empty());
}
void MoveOptimizer::CompressGaps(Instruction* instruction) {
int i = FindFirstNonEmptySlot(instruction);
bool has_moves = i <= Instruction::LAST_GAP_POSITION;
USE(has_moves);
if (i == Instruction::LAST_GAP_POSITION) {
std::swap(instruction->parallel_moves()[Instruction::FIRST_GAP_POSITION],
instruction->parallel_moves()[Instruction::LAST_GAP_POSITION]);
} else if (i == Instruction::FIRST_GAP_POSITION) {
CompressMoves(
instruction->parallel_moves()[Instruction::FIRST_GAP_POSITION],
instruction->parallel_moves()[Instruction::LAST_GAP_POSITION]);
}
// We either have no moves, or, after swapping or compressing, we have
// all the moves in the first gap position, and none in the second/end gap
// position.
ParallelMove* first =
instruction->parallel_moves()[Instruction::FIRST_GAP_POSITION];
ParallelMove* last =
instruction->parallel_moves()[Instruction::LAST_GAP_POSITION];
USE(first);
USE(last);
DCHECK(!has_moves ||
(first != nullptr && (last == nullptr || last->empty())));
}
void MoveOptimizer::CompressBlock(InstructionBlock* block) {
int first_instr_index = block->first_instruction_index();
int last_instr_index = block->last_instruction_index();
// Start by removing gap assignments where the output of the subsequent
// instruction appears on LHS, as long as they are not needed by its input.
Instruction* prev_instr = code()->instructions()[first_instr_index];
RemoveClobberedDestinations(prev_instr);
for (int index = first_instr_index + 1; index <= last_instr_index; ++index) {
Instruction* instr = code()->instructions()[index];
// Migrate to the gap of prev_instr eligible moves from instr.
MigrateMoves(instr, prev_instr);
// Remove gap assignments clobbered by instr's output.
RemoveClobberedDestinations(instr);
prev_instr = instr;
}
}
const Instruction* MoveOptimizer::LastInstruction(
const InstructionBlock* block) const {
return code()->instructions()[block->last_instruction_index()];
}
void MoveOptimizer::OptimizeMerge(InstructionBlock* block) {
DCHECK_LT(1, block->PredecessorCount());
// Ensure that the last instruction in all incoming blocks don't contain
// things that would prevent moving gap moves across them.
for (RpoNumber& pred_index : block->predecessors()) {
const InstructionBlock* pred = code()->InstructionBlockAt(pred_index);
// If the predecessor has more than one successor, we shouldn't attempt to
// move down to this block (one of the successors) any of the gap moves,
// because their effect may be necessary to the other successors.
if (pred->SuccessorCount() > 1) return;
const Instruction* last_instr =
code()->instructions()[pred->last_instruction_index()];
if (last_instr->IsCall()) return;
if (last_instr->TempCount() != 0) return;
if (last_instr->OutputCount() != 0) return;
for (size_t i = 0; i < last_instr->InputCount(); ++i) {
const InstructionOperand* op = last_instr->InputAt(i);
if (!op->IsConstant() && !op->IsImmediate()) return;
}
}
// TODO(dcarney): pass a ZoneStats down for this?
MoveMap move_map(local_zone());
size_t correct_counts = 0;
// Accumulate set of shared moves.
for (RpoNumber& pred_index : block->predecessors()) {
const InstructionBlock* pred = code()->InstructionBlockAt(pred_index);
const Instruction* instr = LastInstruction(pred);
if (instr->parallel_moves()[0] == nullptr ||
instr->parallel_moves()[0]->empty()) {
return;
}
for (const MoveOperands* move : *instr->parallel_moves()[0]) {
if (move->IsRedundant()) continue;
InstructionOperand src = move->source();
InstructionOperand dst = move->destination();
MoveKey key = {src, dst};
auto res = move_map.insert(std::make_pair(key, 1));
if (!res.second) {
res.first->second++;
if (res.first->second == block->PredecessorCount()) {
correct_counts++;
}
}
}
}
if (move_map.empty() || correct_counts == 0) return;
// Find insertion point.
Instruction* instr = code()->instructions()[block->first_instruction_index()];
if (correct_counts != move_map.size()) {
// Moves that are unique to each predecessor won't be pushed to the common
// successor.
OperandSet conflicting_srcs(&operand_buffer1);
for (auto iter = move_map.begin(), end = move_map.end(); iter != end;) {
auto current = iter;
++iter;
if (current->second != block->PredecessorCount()) {
InstructionOperand dest = current->first.destination;
// Not all the moves in all the gaps are the same. Maybe some are. If
// there are such moves, we could move them, but the destination of the
// moves staying behind can't appear as a source of a common move,
// because the move staying behind will clobber this destination.
conflicting_srcs.InsertOp(dest);
move_map.erase(current);
}
}
bool changed = false;
do {
// If a common move can't be pushed to the common successor, then its
// destination also can't appear as source to any move being pushed.
changed = false;
for (auto iter = move_map.begin(), end = move_map.end(); iter != end;) {
auto current = iter;
++iter;
DCHECK_EQ(block->PredecessorCount(), current->second);
if (conflicting_srcs.ContainsOpOrAlias(current->first.source)) {
conflicting_srcs.InsertOp(current->first.destination);
move_map.erase(current);
changed = true;
}
}
} while (changed);
}
if (move_map.empty()) return;
DCHECK_NOT_NULL(instr);
bool gap_initialized = true;
if (instr->parallel_moves()[0] != nullptr &&
!instr->parallel_moves()[0]->empty()) {
// Will compress after insertion.
gap_initialized = false;
std::swap(instr->parallel_moves()[0], instr->parallel_moves()[1]);
}
ParallelMove* moves = instr->GetOrCreateParallelMove(
static_cast<Instruction::GapPosition>(0), code_zone());
// Delete relevant entries in predecessors and move everything to block.
bool first_iteration = true;
for (RpoNumber& pred_index : block->predecessors()) {
const InstructionBlock* pred = code()->InstructionBlockAt(pred_index);
for (MoveOperands* move : *LastInstruction(pred)->parallel_moves()[0]) {
if (move->IsRedundant()) continue;
MoveKey key = {move->source(), move->destination()};
auto it = move_map.find(key);
if (it != move_map.end()) {
if (first_iteration) {
moves->AddMove(move->source(), move->destination());
}
move->Eliminate();
}
}
first_iteration = false;
}
// Compress.
if (!gap_initialized) {
CompressMoves(instr->parallel_moves()[0], instr->parallel_moves()[1]);
}
CompressBlock(block);
}
namespace {
bool IsSlot(const InstructionOperand& op) {
return op.IsStackSlot() || op.IsFPStackSlot();
}
bool LoadCompare(const MoveOperands* a, const MoveOperands* b) {
if (!a->source().EqualsCanonicalized(b->source())) {
return a->source().CompareCanonicalized(b->source());
}
if (IsSlot(a->destination()) && !IsSlot(b->destination())) return false;
if (!IsSlot(a->destination()) && IsSlot(b->destination())) return true;
return a->destination().CompareCanonicalized(b->destination());
}
} // namespace
// 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(Instruction* instr) {
MoveOpVector& loads = local_vector();
DCHECK(loads.empty());
ParallelMove* parallel_moves = instr->parallel_moves()[0];
if (parallel_moves == nullptr) return;
// Find all the loads.
for (MoveOperands* move : *parallel_moves) {
if (move->IsRedundant()) continue;
if (move->source().IsConstant() || IsSlot(move->source())) {
loads.push_back(move);
}
}
if (loads.empty()) return;
// Group the loads by source, moving the preferred destination to the
// beginning of the group.
std::sort(loads.begin(), loads.end(), LoadCompare);
MoveOperands* group_begin = nullptr;
for (MoveOperands* load : loads) {
// New group.
if (group_begin == nullptr ||
!load->source().EqualsCanonicalized(group_begin->source())) {
group_begin = load;
continue;
}
// Nothing to be gained from splitting here.
if (IsSlot(group_begin->destination())) continue;
// Insert new move into slot 1.
ParallelMove* slot_1 = instr->GetOrCreateParallelMove(
static_cast<Instruction::GapPosition>(1), code_zone());
slot_1->AddMove(group_begin->destination(), load->destination());
load->Eliminate();
}
loads.clear();
}
} // namespace compiler
} // namespace internal
} // namespace v8