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

runtime/vm/assembler_arm.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_ARM)
 
 #include "vm/assembler.h"
 #include "vm/cpu.h"
 #include "vm/longjump.h"
@@ skipping 1541 matching lines @@
 
 void Assembler::LoadPoolPointer() {
   const intptr_t object_pool_pc_dist =
      Instructions::HeaderSize() - Instructions::object_pool_offset() +
      CodeSize() + Instr::kPCReadOffset;
   LoadFromOffset(kWord, PP, PC, -object_pool_pc_dist);
 }
 
 
 void Assembler::LoadIsolate(Register rd) {
-  LoadImmediate(rd, reinterpret_cast<uword>(Isolate::Current()));
+  ldr(rd, Address(THR, Thread::isolate_offset()));
 }
 
 
 void Assembler::LoadObject(Register rd, const Object& object, Condition cond) {
   // Smis and VM heap objects are never relocated; do not use object pool.
   if (object.IsSmi()) {
     LoadImmediate(rd, reinterpret_cast<int32_t>(object.raw()), cond);
   } else if (object.InVMHeap() || !allow_constant_pool()) {
     // Make sure that class CallPattern is able to decode this load immediate.
     const int32_t object_raw = reinterpret_cast<int32_t>(object.raw());
@@ skipping 1996 matching lines @@
 
 
 const char* Assembler::FpuRegisterName(FpuRegister reg) {
   ASSERT((0 <= reg) && (reg < kNumberOfFpuRegisters));
   return fpu_reg_names[reg];
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_ARM