[turbofan] Implement jump threading after register allocation.

src/compiler/pipeline.cc

Index: src/compiler/pipeline.cc
diff --git a/src/compiler/pipeline.cc b/src/compiler/pipeline.cc
index 3a0d27b0593f51ad1306350ac95b4cfb25da4093..246bf471b8588a277ee49b1dac625b9a334e74b8 100644
--- a/src/compiler/pipeline.cc
+++ b/src/compiler/pipeline.cc
@@ -21,6 +21,7 @@
 #include "src/compiler/js-generic-lowering.h"
 #include "src/compiler/js-inlining.h"
 #include "src/compiler/js-typed-lowering.h"
+#include "src/compiler/jump-threading.h"
 #include "src/compiler/machine-operator-reducer.h"
 #include "src/compiler/pipeline-statistics.h"
 #include "src/compiler/register-allocator.h"
@@ -578,6 +579,18 @@ struct ResolveControlFlowPhase {
 };
 
 
+struct JumpThreadingPhase {
+  static const char* phase_name() { return "jump threading"; }
+
+  void Run(PipelineData* data, Zone* temp_zone) {
+    ZoneVector<BasicBlock::RpoNumber> result(temp_zone);
+    if (JumpThreading::ComputeForwarding(temp_zone, result, data->sequence())) {
+      JumpThreading::ApplyForwarding(result, data->sequence());
+    }
+  }
+};
+
+
 struct GenerateCodePhase {
   static const char* phase_name() { return "generate code"; }
 
@@ -902,7 +915,10 @@ void Pipeline::GenerateCode(Linkage* linkage) {
 
   BeginPhaseKind("code generation");
 
-  // Generate native sequence.
+  // Optimimize jumps.

[dcarney, 2014/11/24 15:59:09]

if (FLAG_turbo_jt) 

+  Run<JumpThreadingPhase>();
+
+  // Generate final machine code.
   Run<GenerateCodePhase>(linkage);
 
   if (profiler_data != NULL) {