[turbofan] put late ssa deconstruction in register allocator behind a flag

src/compiler/pipeline.cc

Index: src/compiler/pipeline.cc
diff --git a/src/compiler/pipeline.cc b/src/compiler/pipeline.cc
index e5460d1fad6b0ad18221e1defa19d23b52e33fc1..d9a9ec49d24bc4bd99a1c20c548ae86509e7dcfa 100644
--- a/src/compiler/pipeline.cc
+++ b/src/compiler/pipeline.cc
@@ -506,6 +506,15 @@ struct MeetRegisterConstraintsPhase {
 };
 
 
+struct ResolvePhisPhase {
+  static const char* phase_name() { return "resolve phis"; }
+
+  void Run(PipelineData* data, Zone* temp_zone) {
+    data->register_allocator()->ResolvePhis();
+  }
+};
+
+
 struct BuildLiveRangesPhase {
   static const char* phase_name() { return "build live ranges"; }
 
@@ -926,6 +935,7 @@ void Pipeline::AllocateRegisters(const RegisterConfiguration* config,
                                     debug_name.get());
 
   Run<MeetRegisterConstraintsPhase>();
+  Run<ResolvePhisPhase>();
   Run<BuildLiveRangesPhase>();
   if (FLAG_trace_turbo) {
     OFStream os(stdout);