[ia32/x64] Smaller instruction to check NaN

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 1555 matching lines @@
 
 void Assembler::movzxbl(Register dst, const Operand& src) {
   EnsureSpace ensure_space(this);
   emit_optional_rex_32(dst, src);
   emit(0x0F);
   emit(0xB6);
   emit_operand(dst, src);
 }
 
 
+void Assembler::movzxbl(Register dst, Register src) {
+  EnsureSpace ensure_space(this);
+  if (!src.is_byte_register()) {
+    // Register is not one of al, bl, cl, dl.  Its encoding needs REX.
+    emit_rex_32(src);
+  }
+  emit(0x0F);
+  emit(0xB6);
+  emit_modrm(dst, src);
+}
+
+
 void Assembler::movzxwq(Register dst, const Operand& src) {
   EnsureSpace ensure_space(this);
   emit_optional_rex_32(dst, src);
   emit(0x0F);
   emit(0xB7);
   emit_operand(dst, src);
 }
 
 
 void Assembler::movzxwl(Register dst, const Operand& src) {
@@ skipping 1628 matching lines @@
 
 
 bool RelocInfo::IsInConstantPool() {
   return false;
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64