[turbofan] Reenable value numbering.

src/compiler/pipeline.cc

Index: src/compiler/pipeline.cc
diff --git a/src/compiler/pipeline.cc b/src/compiler/pipeline.cc
index 469a7eda4260f55303f25872fd2742b3e50cd833..7da2fb543c9d32c77bad75e558ac262d942b20ce 100644
--- a/src/compiler/pipeline.cc
+++ b/src/compiler/pipeline.cc
@@ -290,14 +290,13 @@ Handle<Code> Pipeline::GenerateCode() {
       SourcePositionTable::Scope pos(&source_positions,
                                      SourcePosition::Unknown());
       Linkage linkage(info());
-      // TODO(turbofan): Value numbering disabled for now.
-      // ValueNumberingReducer vn_reducer(zone());
+      ValueNumberingReducer vn_reducer(zone());
       SimplifiedOperatorReducer simple_reducer(&jsgraph);
       ChangeLowering lowering(&jsgraph, &linkage);
       MachineOperatorReducer mach_reducer(&jsgraph);
       GraphReducer graph_reducer(&graph);
       // TODO(titzer): Figure out if we should run all reducers at once here.
-      // graph_reducer.AddReducer(&vn_reducer);
+      graph_reducer.AddReducer(&vn_reducer);
       graph_reducer.AddReducer(&simple_reducer);
       graph_reducer.AddReducer(&lowering);
       graph_reducer.AddReducer(&mach_reducer);