Removes branches from LoadTaggedClassIdMayBeSmi.

runtime/vm/assembler_arm64.cc

 // Copyright (c) 2014, 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"
 #if defined(TARGET_ARCH_ARM64)
 
 #include "vm/assembler.h"
 #include "vm/cpu.h"
 #include "vm/longjump.h"
@@ skipping 1058 matching lines @@
 
 
 void Assembler::CompareClassId(
     Register object, intptr_t class_id, Register pp) {
   LoadClassId(TMP, object, pp);
   CompareImmediate(TMP, class_id, pp);
 }
 
 
 void Assembler::LoadTaggedClassIdMayBeSmi(Register result, Register object) {
-  Label load, done;
-  tsti(object, kSmiTagMask);
-  b(&load, NE);
-  LoadImmediate(result, Smi::RawValue(kSmiCid), PP);
-  b(&done);
-  Bind(&load);
-  LoadClassId(result, object, PP);
+  ASSERT(result != TMP);
+  ASSERT(object != TMP);
+
+  // Make a copy of object since result and object can be the same register.
+  mov(TMP, object);
+  // 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(), PP);
+  // Check if the object is a Smi.
+  tsti(TMP, kSmiTagMask);
+  // If the object *is* a Smi, load the null object into tmp. o/w leave alone.
+  csel(TMP, result, TMP, EQ);
+  // 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, TMP, PP);
+
+  LoadImmediate(TMP, kSmiCid, PP);
+  // If object is a Smi, move the Smi cid into result. o/w leave alone.
+  csel(result, TMP, result, EQ);
+  // Finally, tag the result.
   SmiTag(result);
-  Bind(&done);
 }
 
 
 // Frame entry and exit.
 void Assembler::ReserveAlignedFrameSpace(intptr_t frame_space) {
   // Reserve space for arguments and align frame before entering
   // the C++ world.
   if (frame_space != 0) {
     AddImmediate(SP, SP, -frame_space, kNoPP);
   }
@@ skipping 285 matching lines @@
     LoadImmediate(TMP, tags, pp);
     StoreFieldToOffset(TMP, instance_reg, Object::tags_offset(), pp);
   } else {
     b(failure);
   }
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_ARM64