Small improvement in x64 assembler

src/x64/assembler-x64.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 1487 matching lines @@
   EnsureSpace ensure_space(this);
   emit_rex_64(dst);
   emit(0xB8 | dst.low_bits());
   emitq(reinterpret_cast<uintptr_t>(value), rmode);
 }
 
 
 void Assembler::movq(Register dst, int64_t value, RelocInfo::Mode rmode) {
   // Non-relocatable values might not need a 64-bit representation.
   if (RelocInfo::IsNone(rmode)) {
-    // Sadly, there is no zero or sign extending move for 8-bit immediates.
-    if (is_int32(value)) {
+    if (is_uint32(value)) {
+      movl(dst, Immediate(static_cast<int32_t>(value)));
+      return;
+    } else if (is_int32(value)) {

[Yang, 2013/02/06 10:28:59]

What is the purpose of this change?

[Zheng Liu, 2013/02/06 11:34:08]

Code might be smaller, as [mov r64, imm32] always have a prefix.
MacroAssembler::Set() did similar things.

[Yang, 2013/02/06 11:39:18]

But this change seems to be to the effect of changing

if (A) {
  B;
} else if (C) {
  D;
}

into

if (C) {
  D;
} else if (A) {
  B;
}

I don't see any difference besides changing the order.

       movq(dst, Immediate(static_cast<int32_t>(value)));
       return;
-    } else if (is_uint32(value)) {
-      movl(dst, Immediate(static_cast<int32_t>(value)));
-      return;
     }
     // Value cannot be represented by 32 bits, so do a full 64 bit immediate
     // value.
   }
   EnsureSpace ensure_space(this);
   emit_rex_64(dst);
   emit(0xB8 | dst.low_bits());
   emitq(value, rmode);
 }
 
@@ skipping 1531 matching lines @@
 bool RelocInfo::IsCodedSpecially() {
   // The deserializer needs to know whether a pointer is specially coded.  Being
   // specially coded on x64 means that it is a relative 32 bit address, as used
   // by branch instructions.
   return (1 << rmode_) & kApplyMask;
 }
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64