[x64] Recognize MOVSXBL.

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 0bcdf24d6f0f236900ca9be05b9ddacfba2e082d..13cbf8ca343c7e0d0bbb92aa5d3fc03cce2db273 100644
--- a/src/x64/assembler-x64.cc
+++ b/src/x64/assembler-x64.cc
@@ -1383,6 +1383,20 @@ void Assembler::movl(const Operand& dst, Label* src) {
 }
 
 
+void Assembler::movsxbl(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(dst, src);
+  } else {
+    emit_optional_rex_32(dst, src);
+  }
+  emit(0x0F);
+  emit(0xBE);
+  emit_modrm(dst, src);
+}
+
+
 void Assembler::movsxbl(Register dst, const Operand& src) {
   EnsureSpace ensure_space(this);
   emit_optional_rex_32(dst, src);