x64: Make sure that the upper half of a 64bit register contains 0 for int32 values.

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 75eeff55387d2dce0a594493e20f6bc494559ebb..19bd82856e4da18fe547069179b6c7b8db94ff66 100644
--- a/src/x64/assembler-x64.cc
+++ b/src/x64/assembler-x64.cc
@@ -1389,6 +1389,15 @@ void Assembler::movl(const Operand& dst, Label* src) {
 }
 
 
+void Assembler::movsxbl(Register dst, const Operand& src) {
+  EnsureSpace ensure_space(this);
+  emit_optional_rex_32(dst, src);
+  emit(0x0F);
+  emit(0xBE);
+  emit_operand(dst, src);
+}
+
+
 void Assembler::movsxbq(Register dst, const Operand& src) {
   EnsureSpace ensure_space(this);
   emit_rex_64(dst, src);
@@ -1398,6 +1407,15 @@ void Assembler::movsxbq(Register dst, const Operand& src) {
 }
 
 
+void Assembler::movsxwl(Register dst, const Operand& src) {
+  EnsureSpace ensure_space(this);
+  emit_optional_rex_32(dst, src);
+  emit(0x0F);
+  emit(0xBF);
+  emit_operand(dst, src);
+}
+
+
 void Assembler::movsxwq(Register dst, const Operand& src) {
   EnsureSpace ensure_space(this);
   emit_rex_64(dst, src);