[turbofan] Improve the store-store elimination.

src/compiler/pipeline.cc

Index: src/compiler/pipeline.cc
diff --git a/src/compiler/pipeline.cc b/src/compiler/pipeline.cc
index 9683a83d68dc7b5c6c6132ce98b30d934476f05f..13bb24d20e0ece90fb6c08cdae425f651782e0f2 100644
--- a/src/compiler/pipeline.cc
+++ b/src/compiler/pipeline.cc
@@ -1032,12 +1032,33 @@ struct EffectControlLinearizationPhase {
   }
 };
 
+// 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);
   }
 };
 
@@ -1518,6 +1539,9 @@ bool PipelineImpl::OptimizeGraph(Linkage* linkage) {
   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);