Cache current thread in a reserved register and use it in LoadIsolate

runtime/vm/assembler_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"  // NOLINT
 #if defined(TARGET_ARCH_MIPS)
 
 #include "vm/assembler.h"
 #include "vm/longjump.h"
 #include "vm/runtime_entry.h"
@@ skipping 608 matching lines @@
   if (Address::CanHoldOffset(offset - kHeapObjectTag)) {
     StoreIntoObjectNoBarrier(object, FieldAddress(object, offset), value);
   } else {
     AddImmediate(TMP, object, offset - kHeapObjectTag);
     StoreIntoObjectNoBarrier(object, Address(TMP), value);
   }
 }
 
 
 void Assembler::LoadIsolate(Register result) {
-  LoadImmediate(result, reinterpret_cast<uword>(Isolate::Current()));
+  lw(result, Address(THR, Thread::isolate_offset()));
 }
 
 
 void Assembler::LoadClassId(Register result, Register object) {
   ASSERT(RawObject::kClassIdTagPos == 16);
   ASSERT(RawObject::kClassIdTagSize == 16);
   const intptr_t class_id_offset = Object::tags_offset() +
       RawObject::kClassIdTagPos / kBitsPerByte;
   lhu(result, FieldAddress(object, class_id_offset));
 }
@@ skipping 571 matching lines @@
   Label stop;
   b(&stop);
   Emit(reinterpret_cast<int32_t>(message));
   Bind(&stop);
   break_(Instr::kStopMessageCode);
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_MIPS