[turbofan] extend escape analysis to reduce CheckMaps

R=bmeurer@chromium.org

BUG=

Review-Url: https://codereview.chromium.org/2680973013
Cr-Original-Commit-Position: refs/heads/master@{#43163}
Committed: https://chromium.googlesource.com/v8/v8/+/f01c8a6e4b24ab38e58bb141fc251bc6b75dbe21
Review-Url: https://codereview.chromium.org/2680973013
Cr-Commit-Position: refs/heads/master@{#43478}

src/compiler/escape-analysis-reducer.cc

@@ -46,6 +46,8 @@ Reduction EscapeAnalysisReducer::ReduceNode(Node* node) {
     case IrOpcode::kStoreField:
     case IrOpcode::kStoreElement:
       return ReduceStore(node);
+    case IrOpcode::kCheckMaps:
+      return ReduceCheckMaps(node);
     case IrOpcode::kAllocate:
       return ReduceAllocate(node);
     case IrOpcode::kFinishRegion:
@@ -171,6 +173,21 @@ Reduction EscapeAnalysisReducer::ReduceStore(Node* node) {
   return NoChange();
 }
 
+Reduction EscapeAnalysisReducer::ReduceCheckMaps(Node* node) {
+  DCHECK(node->opcode() == IrOpcode::kCheckMaps);
+  if (node->id() < static_cast<NodeId>(fully_reduced_.length())) {
+    fully_reduced_.Add(node->id());
+  }
+  if (escape_analysis()->IsVirtual(
+          SkipTypeGuards(NodeProperties::GetValueInput(node, 0))) &&
+      !escape_analysis()->IsEscaped(node)) {
+    TRACE("Removed #%d (%s) from effect chain\n", node->id(),
+          node->op()->mnemonic());
+    RelaxEffectsAndControls(node);
+    return Changed(node);
+  }
+  return NoChange();
+}
 
 Reduction EscapeAnalysisReducer::ReduceAllocate(Node* node) {
   DCHECK_EQ(node->opcode(), IrOpcode::kAllocate);

src/compiler/escape-analysis-reducer.h

@@ -38,6 +38,7 @@ class V8_EXPORT_PRIVATE EscapeAnalysisReducer final
   Reduction ReduceNode(Node* node);
   Reduction ReduceLoad(Node* node);
   Reduction ReduceStore(Node* node);
+  Reduction ReduceCheckMaps(Node* node);
   Reduction ReduceAllocate(Node* node);
   Reduction ReduceFinishRegion(Node* node);
   Reduction ReduceReferenceEqual(Node* node);

src/compiler/escape-analysis.cc

@@ -807,6 +807,7 @@ bool EscapeStatusAnalysis::CheckUsesForEscape(Node* uses, Node* rep,
       case IrOpcode::kStateValues:
       case IrOpcode::kReferenceEqual:
       case IrOpcode::kFinishRegion:
+      case IrOpcode::kCheckMaps:
         if (IsEscaped(use) && SetEscaped(rep)) {
           TRACE(
               "Setting #%d (%s) to escaped because of use by escaping node "
@@ -1124,6 +1125,9 @@ bool EscapeAnalysis::Process(Node* node) {
     case IrOpcode::kLoadElement:
       ProcessLoadElement(node);
       break;
+    case IrOpcode::kCheckMaps:
+      ProcessCheckMaps(node);
+      break;
     case IrOpcode::kStart:
       ProcessStart(node);
       break;
@@ -1161,6 +1165,10 @@ void EscapeAnalysis::ProcessAllocationUsers(Node* node) {
       case IrOpcode::kFinishRegion:
       case IrOpcode::kObjectIsSmi:
         break;
+      case IrOpcode::kCheckMaps: {
+        CheckMapsParameters params = CheckMapsParametersOf(node->op());
+        if (params.flags() == CheckMapsFlag::kNone) break;
+      }  // Fallthrough.
       default:
         VirtualState* state = virtual_states_[node->id()];
         if (VirtualObject* obj =
@@ -1514,6 +1522,46 @@ void EscapeAnalysis::ProcessLoadField(Node* node) {
   }
 }
 
+void EscapeAnalysis::ProcessCheckMaps(Node* node) {
+  DCHECK_EQ(node->opcode(), IrOpcode::kCheckMaps);
+  ForwardVirtualState(node);
+  Node* checked = ResolveReplacement(NodeProperties::GetValueInput(node, 0));
+  if (FLAG_turbo_experimental) {
+    VirtualState* state = virtual_states_[node->id()];
+    if (VirtualObject* object = GetVirtualObject(state, checked)) {
+      if (!object->IsTracked()) {
+        if (status_analysis_->SetEscaped(node)) {
+          TRACE(
+              "Setting #%d (%s) to escaped because checked object #%i is not "
+              "tracked\n",
+              node->id(), node->op()->mnemonic(), object->id());
+        }
+        return;
+      }
+      CheckMapsParameters params = CheckMapsParametersOf(node->op());
+
+      Node* value = object->GetField(HeapObject::kMapOffset / kPointerSize);
+      if (value) {
+        value = ResolveReplacement(value);
+        // TODO(tebbi): We want to extend this beyond constant folding with a
+        // CheckMapsValue operator that takes the load-eliminated map value as
+        // input.
+        if (value->opcode() == IrOpcode::kHeapConstant &&
+            params.maps().contains(ZoneHandleSet<Map>(
+                Handle<Map>::cast(OpParameter<Handle<HeapObject>>(value))))) {
+          TRACE("CheckMaps #%i seems to be redundant (until now).\n",
+                node->id());
+          return;
+        }
+      }
+    }
+  }
+  if (status_analysis_->SetEscaped(node)) {
+    TRACE("Setting #%d (%s) to escaped (checking #%i)\n", node->id(),
+          node->op()->mnemonic(), checked->id());
+  }
+}
+
 void EscapeAnalysis::ProcessLoadElement(Node* node) {
   DCHECK_EQ(node->opcode(), IrOpcode::kLoadElement);
   ForwardVirtualState(node);

src/compiler/escape-analysis.h

@@ -45,6 +45,7 @@ class V8_EXPORT_PRIVATE EscapeAnalysis {
   void ProcessStoreField(Node* node);
   void ProcessLoadElement(Node* node);
   void ProcessStoreElement(Node* node);
+  void ProcessCheckMaps(Node* node);
   void ProcessAllocationUsers(Node* node);
   void ProcessAllocation(Node* node);
   void ProcessFinishRegion(Node* node);

src/flag-definitions.h

@@ -499,6 +499,8 @@ DEFINE_BOOL(turbo_stress_instruction_scheduling, false,
             "randomly schedule instructions to stress dependency tracking")
 DEFINE_BOOL(turbo_store_elimination, true,
             "enable store-store elimination in TurboFan")
+DEFINE_BOOL(turbo_experimental, false,
+            "enable crashing features, for testing purposes only")
 // TODO(turbofan): Rename --crankshaft to --optimize eventually.
 DEFINE_IMPLICATION(turbo, crankshaft)
 

test/mjsunit/compiler/escape-analysis-13.js

+// Copyright 2017 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.
+
+// Flags: --allow-natives-syntax --turbo --turbo-escape --turbo-experimental
+
+function f() {
+  var x = {};
+  x.a = "a";
+  x.b = "b";
+  assertEquals("a", x.a);
+  assertEquals("b", x.b);
+}
+f();
+f();
+% OptimizeFunctionOnNextCall(f);
+f();