Reduce redundant phi nodes after graph building.

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 "src/base/platform/elapsed-timer.h"
 #include "src/compiler/ast-graph-builder.h"
 #include "src/compiler/code-generator.h"
 #include "src/compiler/graph-replay.h"
 #include "src/compiler/graph-visualizer.h"
 #include "src/compiler/instruction.h"
 #include "src/compiler/instruction-selector.h"
 #include "src/compiler/js-context-specialization.h"
 #include "src/compiler/js-generic-lowering.h"
 #include "src/compiler/js-typed-lowering.h"
+#include "src/compiler/phi-reducer.h"
 #include "src/compiler/register-allocator.h"
 #include "src/compiler/schedule.h"
 #include "src/compiler/scheduler.h"
 #include "src/compiler/simplified-lowering.h"
 #include "src/compiler/typer.h"
 #include "src/compiler/verifier.h"
 #include "src/hydrogen.h"
 #include "src/ostreams.h"
 
 namespace v8 {
@@ skipping 110 matching lines @@
   JSGraph jsgraph(&graph, &common, &typer);
   Node* context_node;
   {
     PhaseStats graph_builder_stats(info(), PhaseStats::CREATE_GRAPH,
                                    "graph builder");
     AstGraphBuilderWithPositions graph_builder(info(), &jsgraph,
                                                &source_positions);
     graph_builder.CreateGraph();
     context_node = graph_builder.GetFunctionContext();
   }
+  {
+    PhaseStats phi_reducer_stats(info(), PhaseStats::CREATE_GRAPH,
+                                 "phi reduction");
+    PhiReducer phi_reducer;
+    GraphReducer graph_reducer(&graph);
+    graph_reducer.AddReducer(&phi_reducer);
+    graph_reducer.ReduceGraph();
+    // TODO(mstarzinger): Running reducer once ought to be enough for everyone.
+    graph_reducer.ReduceGraph();
+    graph_reducer.ReduceGraph();
+  }
 
   VerifyAndPrintGraph(&graph, "Initial untyped");
 
   if (FLAG_context_specialization) {
     SourcePositionTable::Scope pos_(&source_positions,
                                     SourcePosition::Unknown());
     // Specialize the code to the context as aggressively as possible.
     JSContextSpecializer spec(info(), &jsgraph, context_node);
     spec.SpecializeToContext();
     VerifyAndPrintGraph(&graph, "Context specialized");
@@ skipping 146 matching lines @@
 }
 
 
 void Pipeline::TearDown() {
   InstructionOperand::TearDownCaches();
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8