X64: Adding macro to load double from memory, and use SSE3 instruction if present.

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 c06bc0c4517581a50811fba07b389bd19e0bf1b0..288c8e2af5c40f9686106485eb3e84a84def4ebf 100644
--- a/src/x64/assembler-x64.cc
+++ b/src/x64/assembler-x64.cc
@@ -2657,6 +2657,17 @@ void Assembler::movapd(XMMRegister dst, XMMRegister src) {
 }
 
 
+void Assembler::movddup(XMMRegister dst, const Operand& src) {
+  ASSERT(CpuFeatures::IsEnabled(SSE3));
+  EnsureSpace ensure_space(this);
+  emit(0xF2);
+  emit_optional_rex_32(dst, src);
+  emit(0x0F);
+  emit(0x12);
+  emit_sse_operand(dst, src);
+}
+
+
 void Assembler::movss(XMMRegister dst, const Operand& src) {
   EnsureSpace ensure_space(this);
   emit(0xF3);  // single