[turbofan] Improve the store-store elimination.

src/compiler/pipeline.cc

 // 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/pipeline.h"
 
 #include <fstream>  // NOLINT(readability/streams)
 #include <sstream>
 
 #include "src/base/adapters.h"
@@ skipping 1014 matching lines @@
     // Post-pass for wiring the control/effects
     // - connect allocating representation changes into the control&effect
     //   chains and lower them,
     // - get rid of the region markers,
     // - introduce effect phis and rewire effects to get SSA again.
     EffectControlLinearizer linearizer(data->jsgraph(), schedule, temp_zone);
     linearizer.Run();
   }
 };
 
+// The store-store elimination greatly benefits from doing a common operator
+// reducer just before it, to eliminate conditional deopts with a constant
+// condition.
+
+struct CommonOperatorReducerPhase {

[Jarin, 2016/07/25 09:52:13]

Rename to DeadCodeEliminationPhase (because that is what it is doing).

[bgeron, 2016/07/27 13:40:37]

Done.

+  static const char* phase_name() { return "common operator reducer"; }
+
+  void Run(PipelineData* data, Zone* temp_zone) {
+    // Run the common operator reducer.
+    JSGraphReducer graph_reducer(data->jsgraph(), temp_zone);
+    DeadCodeElimination dead_code_elimination(&graph_reducer, data->graph(),
+                                              data->common());
+    CommonOperatorReducer common_reducer(&graph_reducer, data->graph(),
+                                         data->common(), data->machine());
+    AddReducer(data, &graph_reducer, &dead_code_elimination);
+    AddReducer(data, &graph_reducer, &common_reducer);
+    graph_reducer.ReduceGraph();
+  }
+};
+
 struct StoreStoreEliminationPhase {
-  static const char* phase_name() { return "Store-store elimination"; }
+  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();
+    GraphTrimmer(temp_zone, data->graph()).TrimGraph();

[Jarin, 2016/07/25 09:52:13]

Could you call the trimming on the roots, too? (As we do right below, in the
LoadEliminationPhase.) Otherwise you are not guaranteed the graph will be really
trimmed.

[bgeron, 2016/07/27 13:40:37]

Done. Actually, I think the graph would be trimmed a bit too far :D

+
+    StoreStoreElimination::Run(data->jsgraph(), temp_zone);
   }
 };
 
 struct LoadEliminationPhase {
   static const char* phase_name() { return "load elimination"; }
 
   void Run(PipelineData* data, Zone* temp_zone) {
     // The memory optimizer requires the graphs to be trimmed, so trim now.
     GraphTrimmer trimmer(temp_zone, data->graph());
     NodeVector roots(temp_zone);
@@ skipping 460 matching lines @@
 }
 
 bool PipelineImpl::OptimizeGraph(Linkage* linkage) {
   PipelineData* data = this->data_;
 
   data->BeginPhaseKind("block building");
 
   Run<EffectControlLinearizationPhase>();
   RunPrintAndVerify("Effect and control linearized", true);
 
+  Run<CommonOperatorReducerPhase>();
+  RunPrintAndVerify("Common operator reducer", true);
+
   if (FLAG_turbo_store_elimination) {
     Run<StoreStoreEliminationPhase>();
     RunPrintAndVerify("Store-store elimination", true);
   }
 
   // Optimize control flow.
   if (FLAG_turbo_cf_optimization) {
     Run<ControlFlowOptimizationPhase>();
     RunPrintAndVerify("Control flow optimized", true);
   }
@@ skipping 329 matching lines @@
   data->DeleteRegisterAllocationZone();
 }
 
 CompilationInfo* PipelineImpl::info() const { return data_->info(); }
 
 Isolate* PipelineImpl::isolate() const { return info()->isolate(); }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8