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

runtime/vm/assembler_x64.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"  // NOLINT
 #if defined(TARGET_ARCH_X64)
 
 #include "vm/assembler.h"
 #include "vm/cpu.h"
 #include "vm/heap.h"
@@ skipping 3658 matching lines @@
   SmiUntag(object);
   j(NOT_CARRY, is_smi, kNearJump);
   // Load cid: can't use LoadClassId, object is untagged. Use TIMES_2 scale
   // factor in the addressing mode to compensate for this.
   movl(TMP, Address(object, TIMES_2, class_id_offset));
   cmpl(TMP, Immediate(class_id));
 }
 
 
 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);
 }
 
 
 Address Assembler::ElementAddressForIntIndex(bool is_external,
                                              intptr_t cid,
                                              intptr_t index_scale,
                                              Register array,
                                              intptr_t index) {
   if (is_external) {
     return Address(array, index * index_scale);
@@ skipping 60 matching lines @@
 
 
 const char* Assembler::FpuRegisterName(FpuRegister reg) {
   ASSERT((0 <= reg) && (reg < kNumberOfXmmRegisters));
   return xmm_reg_names[reg];
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64