[turbofan] optimize moves into merges

BUG=

Review URL: https://codereview.chromium.org/755323011

Cr-Commit-Position: refs/heads/master@{#26819}

src/compiler/instruction.h

@@ -82,6 +82,11 @@ class InstructionOperand {
     ConvertTo(kind, index, kInvalidVirtualRegister);
   }
 
+  // Useful for map/set keys.
+  bool operator<(const InstructionOperand& op) const {
+    return value_ < op.value_;
+  }
+
  protected:
   template <typename SubKindOperand>
   static SubKindOperand* New(Zone* zone, const SubKindOperand& op) {

src/compiler/move-optimizer.cc

@@ -10,6 +10,11 @@ namespace compiler {
 
 namespace {
 
+typedef std::pair<InstructionOperand, InstructionOperand> MoveKey;
+typedef ZoneMap<MoveKey, unsigned> MoveMap;
+typedef ZoneSet<InstructionOperand> OperandSet;
+
+
 bool GapsCanMoveOver(Instruction* instr) {
   DCHECK(!instr->IsGapMoves());
   return instr->IsSourcePosition() || instr->IsNop();
@@ -48,6 +53,10 @@ void MoveOptimizer::Run() {
   for (auto* block : code()->instruction_blocks()) {
     CompressBlock(block);
   }
+  for (auto block : code()->instruction_blocks()) {
+    if (block->PredecessorCount() <= 1) continue;
+    OptimizeMerge(block);
+  }
   for (auto gap : to_finalize_) {
     FinalizeMoves(gap);
   }
@@ -130,6 +139,107 @@ void MoveOptimizer::CompressBlock(InstructionBlock* block) {
 }
 
 
+GapInstruction* MoveOptimizer::LastGap(InstructionBlock* block) {
+  int gap_index = block->last_instruction_index() - 1;
+  auto instr = code()->instructions()[gap_index];
+  return GapInstruction::cast(instr);
+}
+
+
+void MoveOptimizer::OptimizeMerge(InstructionBlock* block) {
+  DCHECK(block->PredecessorCount() > 1);
+  // Ensure that the last instruction in all incoming blocks don't contain
+  // things that would prevent moving gap moves across them.
+  for (auto pred_index : block->predecessors()) {
+    auto pred = code()->InstructionBlockAt(pred_index);
+    auto last_instr = code()->instructions()[pred->last_instruction_index()];
+    DCHECK(!last_instr->IsGapMoves());
+    if (last_instr->IsSourcePosition()) continue;
+    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) {
+      auto op = last_instr->InputAt(i);
+      if (!op->IsConstant() && !op->IsImmediate()) return;
+    }
+  }
+  // TODO(dcarney): pass a ZonePool down for this?
+  MoveMap move_map(local_zone());
+  size_t correct_counts = 0;
+  // Accumulate set of shared moves.
+  for (auto pred_index : block->predecessors()) {
+    auto pred = code()->InstructionBlockAt(pred_index);
+    auto gap = LastGap(pred);
+    if (gap->parallel_moves()[0] == nullptr ||
+        gap->parallel_moves()[0]->move_operands()->is_empty()) {
+      return;
+    }
+    auto move_ops = gap->parallel_moves()[0]->move_operands();
+    for (auto op = move_ops->begin(); op != move_ops->end(); ++op) {
+      if (op->IsRedundant()) continue;
+      auto src = *op->source();
+      auto dst = *op->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 != move_map.size()) return;
+  // Find insertion point.
+  GapInstruction* gap = nullptr;
+  for (int i = block->first_instruction_index();
+       i <= block->last_instruction_index(); ++i) {
+    auto instr = code()->instructions()[i];
+    if (instr->IsGapMoves()) {
+      gap = GapInstruction::cast(instr);
+      continue;
+    }
+    if (!GapsCanMoveOver(instr)) break;
+  }
+  DCHECK(gap != nullptr);
+  bool gap_initialized = true;
+  if (gap->parallel_moves()[0] == nullptr ||
+      gap->parallel_moves()[0]->move_operands()->is_empty()) {
+    to_finalize_.push_back(gap);
+  } else {
+    // Will compress after insertion.
+    gap_initialized = false;
+    std::swap(gap->parallel_moves()[0], gap->parallel_moves()[1]);
+  }
+  auto move = gap->GetOrCreateParallelMove(
+      static_cast<GapInstruction::InnerPosition>(0), code_zone());
+  // Delete relevant entries in predecessors and move everything to block.
+  bool first_iteration = true;
+  for (auto pred_index : block->predecessors()) {
+    auto pred = code()->InstructionBlockAt(pred_index);
+    auto gap = LastGap(pred);
+    auto move_ops = gap->parallel_moves()[0]->move_operands();
+    for (auto op = move_ops->begin(); op != move_ops->end(); ++op) {
+      if (op->IsRedundant()) continue;
+      MoveKey key = {*op->source(), *op->destination()};
+      auto it = move_map.find(key);
+      USE(it);
+      DCHECK(it != move_map.end());
+      if (first_iteration) {
+        move->AddMove(op->source(), op->destination(), code_zone());
+      }
+      op->Eliminate();
+    }
+    first_iteration = false;
+  }
+  // Compress.
+  if (!gap_initialized) {
+    CompressMoves(&temp_vector_0(), gap->parallel_moves()[0],
+                  gap->parallel_moves()[1]);
+  }
+}
+
+
 // 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) {

src/compiler/move-optimizer.h

@@ -30,6 +30,8 @@ class MoveOptimizer FINAL {
   void CompressBlock(InstructionBlock* blocke);
   void CompressMoves(MoveOpVector* eliminated, ParallelMove* left,
                      ParallelMove* right);
+  GapInstruction* LastGap(InstructionBlock* block);
+  void OptimizeMerge(InstructionBlock* block);
   void FinalizeMoves(GapInstruction* gap);
 
   Zone* const local_zone_;

src/compiler/register-allocator-verifier.cc

@@ -245,8 +245,7 @@ class PhiMap : public ZoneMap<int, PhiData*>, public ZoneObject {
 struct OperandLess {
   bool operator()(const InstructionOperand* a,
                   const InstructionOperand* b) const {
-    if (a->kind() == b->kind()) return a->index() < b->index();
-    return a->kind() < b->kind();
+    return *a < *b;
   }
 };
 

test/unittests/compiler/move-optimizer-unittest.cc

@@ -124,6 +124,59 @@ TEST_F(MoveOptimizerTest, SplitsConstants) {
   CHECK(Contains(move, Reg(0), Slot(2)));
 }
 
+
+TEST_F(MoveOptimizerTest, SimpleMerge) {
+  StartBlock();
+  EndBlock(Branch(Imm(), 1, 2));
+
+  StartBlock();
+  EndBlock(Jump(2));
+  AddMove(LastGap(), Reg(0), Reg(1));
+
+  StartBlock();
+  EndBlock(Jump(1));
+  AddMove(LastGap(), Reg(0), Reg(1));
+
+  StartBlock();
+  EndBlock(Last());
+
+  Optimize();
+
+  auto move = LastGap()->parallel_moves()[0];
+  CHECK_EQ(1, NonRedundantSize(move));
+  CHECK(Contains(move, Reg(0), Reg(1)));
+}
+
+
+TEST_F(MoveOptimizerTest, SimpleMergeCycle) {
+  StartBlock();
+  EndBlock(Branch(Imm(), 1, 2));
+
+  StartBlock();
+  EndBlock(Jump(2));
+  auto gap_0 = LastGap();
+  AddMove(gap_0, Reg(0), Reg(1));
+  AddMove(LastGap(), Reg(1), Reg(0));
+
+  StartBlock();
+  EndBlock(Jump(1));
+  auto gap_1 = LastGap();
+  AddMove(gap_1, Reg(0), Reg(1));
+  AddMove(gap_1, Reg(1), Reg(0));
+
+  StartBlock();
+  EndBlock(Last());
+
+  Optimize();
+
+  CHECK(gap_0->IsRedundant());
+  CHECK(gap_1->IsRedundant());
+  auto move = LastGap()->parallel_moves()[0];
+  CHECK_EQ(2, NonRedundantSize(move));
+  CHECK(Contains(move, Reg(0), Reg(1)));
+  CHECK(Contains(move, Reg(1), Reg(0)));
+}
+
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8