Revert "Optimizations to IC stub for unoptimized code performance on x64."

runtime/vm/assembler_x64.cc

Index: runtime/vm/assembler_x64.cc
diff --git a/runtime/vm/assembler_x64.cc b/runtime/vm/assembler_x64.cc
index 7b2f39107c29fae43a29f253999449fa64b0fdb4..20541ef5e69d2c9eb0194b38fce817784577eb87 100644
--- a/runtime/vm/assembler_x64.cc
+++ b/runtime/vm/assembler_x64.cc
@@ -3676,56 +3676,29 @@ void Assembler::SmiUntagOrCheckClass(Register object,
 
 
 void Assembler::LoadClassIdMayBeSmi(Register result, Register object) {
-  Label smi;
+  ASSERT(result != object);
 
-  if (result == object) {
-    Label join;
+  // Load up a null object. We only need it so we can use LoadClassId on it in
+  // the case that object is a Smi.
+  LoadObject(result, Object::null_object());
+  // Check if the object is a Smi.
+  testq(object, Immediate(kSmiTagMask));
+  // If the object *is* a Smi, use the null object instead.
+  cmoveq(object, result);
+  // Loads either the cid of the object if it isn't a Smi, or the cid of null
+  // if it is a Smi, which will be ignored.
+  LoadClassId(result, object);
 
-    testq(object, Immediate(kSmiTagMask));
-    j(EQUAL, &smi, Assembler::kNearJump);
-    LoadClassId(result, object);
-    jmp(&join, Assembler::kNearJump);
-
-    Bind(&smi);
-    movq(result, Immediate(kSmiCid));
-
-    Bind(&join);
-  } else {
-    testq(object, Immediate(kSmiTagMask));
-    movq(result, Immediate(kSmiCid));
-    j(EQUAL, &smi, Assembler::kNearJump);
-    LoadClassId(result, object);
-
-    Bind(&smi);
-  }
+  movq(TMP, Immediate(kSmiCid));
+  // If object is a Smi, move the Smi cid into result. o/w leave alone.
+  cmoveq(result, TMP);
 }
 
 
 void Assembler::LoadTaggedClassIdMayBeSmi(Register result, Register object) {
-  Label smi;
-
-  if (result == object) {
-    Label join;
-
-    testq(object, Immediate(kSmiTagMask));
-    j(EQUAL, &smi, Assembler::kNearJump);
-    LoadClassId(result, object);
-    SmiTag(result);
-    jmp(&join, Assembler::kNearJump);
-
-    Bind(&smi);
-    movq(result, Immediate(Smi::RawValue(kSmiCid)));
-
-    Bind(&join);
-  } else {
-    testq(object, Immediate(kSmiTagMask));
-    movq(result, Immediate(kSmiCid));
-    j(EQUAL, &smi, Assembler::kNearJump);
-    LoadClassId(result, object);
-
-    Bind(&smi);
-    SmiTag(result);
-  }
+  LoadClassIdMayBeSmi(result, object);
+  // Finally, tag the result.
+  SmiTag(result);
 }