Add flag --trace-phase to selectively produce IR trace output.

src/ia32/lithium-codegen-ia32.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 49 matching lines @@
  private:
   LCodeGen* codegen_;
   LPointerMap* pointers_;
   Safepoint::DeoptMode deopt_mode_;
 };
 
 
 #define __ masm()->
 
 bool LCodeGen::GenerateCode() {
-  HPhase phase("Code generation", chunk());
+  HPhase phase("Z Code generation", chunk());
   ASSERT(is_unused());
   status_ = GENERATING;
   CpuFeatures::Scope scope(SSE2);
 
   CodeStub::GenerateFPStubs();
 
   // Open a frame scope to indicate that there is a frame on the stack.  The
   // MANUAL indicates that the scope shouldn't actually generate code to set up
   // the frame (that is done in GeneratePrologue).
   FrameScope frame_scope(masm_, StackFrame::MANUAL);
@@ skipping 4769 matching lines @@
                               FixedArray::kHeaderSize - kPointerSize));
   __ bind(&done);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32