Introduce PushInt64AsTwoSmis and PopInt64AsTwoSmis macro instructions for X64

src/x64/macro-assembler-x64.cc

Index: src/x64/macro-assembler-x64.cc
diff --git a/src/x64/macro-assembler-x64.cc b/src/x64/macro-assembler-x64.cc
index 9c9b1620e586ce5872bbc46de2eaf515266716a0..b0830c2b1963298194c5dc9964f024f708562fcf 100644
--- a/src/x64/macro-assembler-x64.cc
+++ b/src/x64/macro-assembler-x64.cc
@@ -2222,6 +2222,30 @@ void MacroAssembler::AddSmiField(Register dst, const Operand& src) {
 }
 
 
+void MacroAssembler::PushInt64AsTwoSmis(Register src, Register scratch) {
+  movq(scratch, src);
+  // High bits.
+  shr(src, Immediate(64 - kSmiShift));
+  shl(src, Immediate(kSmiShift));
+  push(src);
+  // Low bits.
+  shl(scratch, Immediate(kSmiShift));
+  push(scratch);
+}
+
+
+void MacroAssembler::PopInt64AsTwoSmis(Register dst, Register scratch) {
+  pop(scratch);
+  // Low bits.
+  shr(scratch, Immediate(kSmiShift));
+  pop(dst);
+  shr(dst, Immediate(kSmiShift));
+  // High bits.
+  shl(dst, Immediate(64 - kSmiShift));
+  or_(dst, scratch);
+}
+
+
 void MacroAssembler::JumpIfNotString(Register object,
                                      Register object_map,
                                      Label* not_string,