Use shorter write-barrier filtering sequence when value is known to be non-smi.

runtime/vm/assembler_x64_test.cc

Index: runtime/vm/assembler_x64_test.cc
diff --git a/runtime/vm/assembler_x64_test.cc b/runtime/vm/assembler_x64_test.cc
index ba9959137bb7cfb537674db3d071486c253a9a4d..1287571390502b17f76b85497edbc4bc013172fe 100644
--- a/runtime/vm/assembler_x64_test.cc
+++ b/runtime/vm/assembler_x64_test.cc
@@ -2025,6 +2025,20 @@ ASSEMBLER_TEST_RUN(TestNot, test) {
 }
 
 
+ASSEMBLER_TEST_GENERATE(TestNotInt32, assembler) {
+  __ movq(RAX, Immediate(0x0));
+  __ notl(RAX);
+  __ ret();
+}
+
+
+ASSEMBLER_TEST_RUN(TestNotInt32, test) {
+  typedef int (*TestNot)();
+  unsigned int res = reinterpret_cast<TestNot>(test->entry())();
+  EXPECT_EQ(0xFFFFFFFF, res);
+}
+
+
 ASSEMBLER_TEST_GENERATE(XorpdZeroing, assembler) {
   __ pushq(RAX);
   __ movsd(Address(RSP, 0), XMM0);