Port r7868 (constant masking) to 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 7d5d6d3d0b10defc04d30d21a3c103bab7e53413..cda7549df5e24bc2b8ef53478101b2cb85ef1522 100644
--- a/src/x64/macro-assembler-x64.cc
+++ b/src/x64/macro-assembler-x64.cc
@@ -892,6 +892,38 @@ void MacroAssembler::Set(const Operand& dst, int64_t x) {
   }
 }
 
+
+bool MacroAssembler::IsUnsafeInt(const int x) {
+  static const int kMaxBits = 17;
+  return !is_intn(x, kMaxBits);
+}
+
+
+void MacroAssembler::SafeMove(Register dst, Smi* src) {
+  ASSERT(!dst.is(kScratchRegister));
+  ASSERT(kSmiValueSize == 32);  // JIT cookie can be converted to Smi.
+  if (IsUnsafeInt(src->value()) && jit_cookie() != 0) {
+    Move(dst, Smi::FromInt(src->value() ^ jit_cookie()));
+    Move(kScratchRegister, Smi::FromInt(jit_cookie()));
+    xor_(dst, kScratchRegister);
+  } else {
+    Move(dst, src);
+  }
+}
+
+
+void MacroAssembler::SafePush(Smi* src) {
+  ASSERT(kSmiValueSize == 32);  // JIT cookie can be converted to Smi.
+  if (IsUnsafeInt(src->value()) && jit_cookie() != 0) {
+    Push(Smi::FromInt(src->value() ^ jit_cookie()));
+    Move(kScratchRegister, Smi::FromInt(jit_cookie()));
+    xor_(Operand(rsp, 0), kScratchRegister);
+  } else {
+    Push(src);
+  }
+}
+
+
 // ----------------------------------------------------------------------------
 // Smi tagging, untagging and tag detection.