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

src/arm/lithium-codegen-arm.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 44 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 scope1(VFP3);
   CpuFeatures::Scope scope2(ARMv7);
 
   CodeStub::GenerateFPStubs();
 
   // Open a frame scope to indicate that there is a frame on the stack.  The
   // NONE indicates that the scope shouldn't actually generate code to set up
   // the frame (that is done in GeneratePrologue).
@@ skipping 4900 matching lines @@
   __ sub(scratch, result, Operand(index, LSL, kPointerSizeLog2 - kSmiTagSize));
   __ ldr(result, FieldMemOperand(scratch,
                                  FixedArray::kHeaderSize - kPointerSize));
   __ bind(&done);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal