ARM: Improve code aging sequence.

src/arm/full-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 151 matching lines @@
   // the frame (that is done below).
   FrameScope frame_scope(masm_, StackFrame::MANUAL);
 
   info->set_prologue_offset(masm_->pc_offset());
   {
     PredictableCodeSizeScope predictible_code_size_scope(
         masm_, kNoCodeAgeSequenceLength * Assembler::kInstrSize);
     // The following three instructions must remain together and unmodified
     // for code aging to work properly.
     __ stm(db_w, sp, r1.bit() | cp.bit() | fp.bit() | lr.bit());
-    // Load undefined value here, so the value is ready for the loop
-    // below.
-    __ LoadRoot(ip, Heap::kUndefinedValueRootIndex);
+    __ nop(ip.code());
     // Adjust FP to point to saved FP.
     __ add(fp, sp, Operand(2 * kPointerSize));
   }
   info->AddNoFrameRange(0, masm_->pc_offset());
 
   { Comment cmnt(masm_, "[ Allocate locals");
     int locals_count = info->scope()->num_stack_slots();
     // Generators allocate locals, if any, in context slots.
     ASSERT(!info->function()->is_generator() || locals_count == 0);
-    for (int i = 0; i < locals_count; i++) {
-      __ push(ip);
+    if (locals_count > 0) {
+      __ LoadRoot(ip, Heap::kUndefinedValueRootIndex);
+      for (int i = 0; i < locals_count; i++) {
+        __ push(ip);
+      }
     }
   }
 
   bool function_in_register = true;
 
   // Possibly allocate a local context.
   int heap_slots = info->scope()->num_heap_slots() - Context::MIN_CONTEXT_SLOTS;
   if (heap_slots > 0) {
     // Argument to NewContext is the function, which is still in r1.
     Comment cmnt(masm_, "[ Allocate context");
@@ skipping 4716 matching lines @@
   *context_length = 0;
   return previous_;
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_ARM