VM: Avoid smi-check when loading class-ids from known non-smi values

runtime/vm/intermediate_language_mips.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"  // Needed here to get TARGET_ARCH_MIPS.
 #if defined(TARGET_ARCH_MIPS)
 
 #include "vm/intermediate_language.h"
 
 #include "vm/compiler.h"
@@ skipping 1117 matching lines @@
   return LocationSummary::Make(zone,
                                kNumInputs,
                                Location::RequiresRegister(),
                                LocationSummary::kNoCall);
 }
 
 
 void LoadClassIdInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
   Register object = locs()->in(0).reg();
   Register result = locs()->out(0).reg();
-  __ LoadTaggedClassIdMayBeSmi(result, object);
+  const AbstractType& value_type = *this->object()->Type()->ToAbstractType();
+  if (CompileType::Smi().IsAssignableTo(value_type) ||
+      value_type.IsTypeParameter()) {
+    __ LoadTaggedClassIdMayBeSmi(result, object);
+  } else {
+    __ LoadClassId(result, object);
+    __ SmiTag(result);
+  }
 }
 
 
 CompileType LoadIndexedInstr::ComputeType() const {
   switch (class_id_) {
     case kArrayCid:
     case kImmutableArrayCid:
       return CompileType::Dynamic();
 
     case kTypedDataFloat32ArrayCid:
@@ skipping 4563 matching lines @@
                                 1,
                                 locs());
   __ lw(result, Address(SP, 1 * kWordSize));
   __ addiu(SP, SP, Immediate(2 * kWordSize));
 }
 
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_MIPS