[compiler] Introduce a simple store-store elimination, disabled by default.

R=jarin@chromium.org
BUG=

Review-Url: https://codereview.chromium.org/2087483003
Cr-Commit-Position: refs/heads/master@{#37220}

BUILD.gn

@@ -998,6 +998,8 @@ v8_source_set("v8_base") {
     "src/compiler/source-position.h",
     "src/compiler/state-values-utils.cc",
     "src/compiler/state-values-utils.h",
+    "src/compiler/store-store-elimination.cc",
+    "src/compiler/store-store-elimination.h",
     "src/compiler/tail-call-optimization.cc",
     "src/compiler/tail-call-optimization.h",
     "src/compiler/type-hint-analyzer.cc",

src/compiler/pipeline.cc

@@ -58,6 +58,7 @@
 #include "src/compiler/simplified-lowering.h"
 #include "src/compiler/simplified-operator-reducer.h"
 #include "src/compiler/simplified-operator.h"
+#include "src/compiler/store-store-elimination.h"
 #include "src/compiler/tail-call-optimization.h"
 #include "src/compiler/type-hint-analyzer.h"
 #include "src/compiler/typer.h"
@@ -1031,6 +1032,15 @@ struct EffectControlLinearizationPhase {
   }
 };
 
+struct StoreStoreEliminationPhase {
+  static const char* phase_name() { return "Store-store elimination"; }
+
+  void Run(PipelineData* data, Zone* temp_zone) {
+    StoreStoreElimination store_store_elimination(data->jsgraph(), temp_zone);
+    store_store_elimination.Run();
+  }
+};
+
 struct MemoryOptimizationPhase {
   static const char* phase_name() { return "memory optimization"; }
 
@@ -1474,6 +1484,11 @@ bool PipelineImpl::OptimizeGraph(Linkage* linkage) {
   Run<EffectControlLinearizationPhase>();
   RunPrintAndVerify("Effect and control linearized", true);
 
+  if (FLAG_turbo_store_elimination) {
+    Run<StoreStoreEliminationPhase>();
+    RunPrintAndVerify("Store-store elimination", true);
+  }
+
   Run<BranchEliminationPhase>();
   RunPrintAndVerify("Branch conditions eliminated", true);
 

src/compiler/store-store-elimination.h

+// Copyright 2016 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.
+
+#ifndef V8_COMPILER_STORE_STORE_ELIMINATION_H_
+#define V8_COMPILER_STORE_STORE_ELIMINATION_H_
+
+#include "src/compiler/common-operator.h"
+#include "src/compiler/graph-reducer.h"
+#include "src/compiler/js-graph.h"
+
+namespace v8 {
+namespace internal {
+namespace compiler {
+
+// Forward declarations.
+class CommonOperatorBuilder;
+class JSGraph;
+
+class StoreStoreElimination final {
+ public:
+  StoreStoreElimination(JSGraph* js_graph, Zone* temp_zone);
+  ~StoreStoreElimination();
+  void Run();
+
+ private:
+  static bool IsEligibleNode(Node* node);
+  void ReduceEligibleNode(Node* node);
+  JSGraph* jsgraph() const { return jsgraph_; }
+  Zone* temp_zone() const { return temp_zone_; }
+
+  JSGraph* const jsgraph_;
+  Zone* const temp_zone_;
+};
+
+}  // namespace compiler
+}  // namespace internal
+}  // namespace v8
+
+#endif  // V8_COMPILER_STORE_STORE_ELIMINATION_H_

src/flag-definitions.h

@@ -483,6 +483,8 @@ DEFINE_BOOL(turbo_instruction_scheduling, false,
             "enable instruction scheduling in TurboFan")
 DEFINE_BOOL(turbo_stress_instruction_scheduling, false,
             "randomly schedule instructions to stress dependency tracking")
+DEFINE_BOOL(turbo_store_elimination, false,
+            "enable store-store elimination in TurboFan")
 
 // Flags for native WebAssembly.
 DEFINE_BOOL(expose_wasm, false, "expose WASM interface to JavaScript")

src/v8.gyp

@@ -662,6 +662,8 @@
         'compiler/source-position.h',
         'compiler/state-values-utils.cc',
         'compiler/state-values-utils.h',
+        'compiler/store-store-elimination.cc',
+        'compiler/store-store-elimination.h',
         'compiler/tail-call-optimization.cc',
         'compiler/tail-call-optimization.h',
         'compiler/type-hint-analyzer.cc',