Cleanup of class id loading sequences.

runtime/vm/assembler_mips.cc

Index: runtime/vm/assembler_mips.cc
===================================================================
--- runtime/vm/assembler_mips.cc	(revision 38317)
+++ runtime/vm/assembler_mips.cc	(working copy)
@@ -692,26 +692,15 @@
 
 
 void Assembler::LoadTaggedClassIdMayBeSmi(Register result, Register object) {
-  ASSERT(object != TMP);
-  ASSERT(result != TMP);
+  static const intptr_t kSmiCidSource = kSmiCid << RawObject::kClassIdTagPos;
 
-  // 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.
-  LoadImmediate(result, reinterpret_cast<intptr_t>(Object::null()));
-  // Check if the object is a Smi.
-  andi(CMPRES1, TMP, Immediate(kSmiTagMask));
-  // If the object *is* a Smi, load the null object into tmp. o/w leave alone.
-  movz(TMP, result, CMPRES1);
-  // 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);
-
-  LoadImmediate(TMP, kSmiCid);
-  // If object is a Smi, move the Smi cid into result. o/w leave alone.
+  LoadImmediate(TMP, reinterpret_cast<int32_t>(&kSmiCidSource) + 1);
+  andi(CMPRES1, object, Immediate(kSmiTagMask));
+  if (result != object) {
+    mov(result, object);
+  }
   movz(result, TMP, CMPRES1);
-  // Finally, tag the result.
+  LoadClassId(result, result);
   SmiTag(result);
 }