[ia32/x64] Smaller instruction to check NaN

src/x64/assembler-x64.cc

Index: src/x64/assembler-x64.cc
diff --git a/src/x64/assembler-x64.cc b/src/x64/assembler-x64.cc
index 53d45bb2156635647a35224d57069886cc80372f..27275d0d9acb041e744716ca1ad6df1d4df7e507 100644
--- a/src/x64/assembler-x64.cc
+++ b/src/x64/assembler-x64.cc
@@ -1573,6 +1573,18 @@ void Assembler::movzxbl(Register dst, const Operand& 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);