Prefer r0 as TOS when performing virtual frame dup on ARM

src/arm/virtual-frame-arm.cc

 // Copyright 2009 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 487 matching lines @@
 
 void VirtualFrame::Dup() {
   AssertIsNotSpilled();
   switch (top_of_stack_state_) {
     case NO_TOS_REGISTERS:
       __ ldr(r0, MemOperand(sp, 0));
       top_of_stack_state_ = R0_TOS;
       break;
     case R0_TOS:
       __ mov(r1, r0);
+      // r0 and r1 contains the same value. Prefer a state with r0 holding TOS.
       top_of_stack_state_ = R0_R1_TOS;
       break;
     case R1_TOS:
       __ mov(r0, r1);
+      // r0 and r1 contains the same value. Prefer a state with r0 holding TOS.
       top_of_stack_state_ = R0_R1_TOS;
       break;
     case R0_R1_TOS:
       __ push(r1);
       __ mov(r1, r0);
-      // No need to change state as r0 and r1 now contains the same value.
+      // r0 and r1 contains the same value. Prefer a state with r0 holding TOS.
+      top_of_stack_state_ = R0_R1_TOS;
       break;
     case R1_R0_TOS:
       __ push(r0);
       __ mov(r0, r1);
-      // No need to change state as r0 and r1 now contains the same value.
+      // r0 and r1 contains the same value. Prefer a state with r0 holding TOS.
+      top_of_stack_state_ = R0_R1_TOS;
       break;
     default:
       UNREACHABLE();
   }
   element_count_++;
 }
 
 
 Register VirtualFrame::PopToRegister(Register but_not_to_this_one) {
   ASSERT(but_not_to_this_one.is(r0) ||
@@ skipping 126 matching lines @@
     default:
       UNREACHABLE();
       break;
   }
   ASSERT(register_allocation_map_ == 0);  // Not yet implemented.
 }
 
 #undef __
 
 } }  // namespace v8::internal