Optionally use 31-bits SMI value for 64-bit system

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 f5939c3b7e1f1604d18528fe2cdd5d9481061132..f47051165fc5b109d99593d3926fc97391fb4041 100644
--- a/src/x64/assembler-x64.cc
+++ b/src/x64/assembler-x64.cc
@@ -3029,6 +3029,15 @@ void Assembler::movmskps(Register dst, XMMRegister src) {
 }
 
 
+void Assembler::pcmpeqd(XMMRegister dst, XMMRegister src) {
+  EnsureSpace ensure_space(this);
+  emit(0x66);
+  emit(0x0f);
+  emit(0x76);
+  emit_sse_operand(dst, src);
+}
+
+
 void Assembler::emit_sse_operand(XMMRegister reg, const Operand& adr) {
   Register ireg = { reg.code() };
   emit_operand(ireg, adr);