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

runtime/vm/constants_mips.h

 // 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.
 
 #ifndef VM_CONSTANTS_MIPS_H_
 #define VM_CONSTANTS_MIPS_H_
 
 #include "platform/assert.h"
 
 namespace dart {
@@ skipping 167 matching lines @@
 // Register aliases.
 const Register TMP = AT;  // Used as scratch register by assembler.
 const Register TMP2 = kNoRegister;  // No second assembler scratch register.
 const Register CTX = S6;  // Location of current context at method entry.
 const Register PP = S7;  // Caches object pool pointer in generated code.
 const Register SPREG = SP;  // Stack pointer register.
 const Register FPREG = FP;  // Frame pointer register.
 const Register LRREG = RA;  // Link register.
 const Register ICREG = S5;  // IC data register.
 const Register ARGS_DESC_REG = S4;
+const Register THR = S3;  // Caches current thread in generated code.
 
 // The code that generates a comparison can be far away from the code that
 // generates the branch that uses the result of that comparison. In this case,
 // CMPRES1 and CMPRES2 are used for the results of the comparison. We need two
 // since TMP is clobbered by a far branch.
 const Register CMPRES1 = T8;
 const Register CMPRES2 = T9;
 
 // Exception object is passed in this register to the catch handlers when an
 // exception is thrown.
@@ skipping 441 matching lines @@
 #endif  // defined(DEBUG)
 
  private:
   DISALLOW_ALLOCATION();
   DISALLOW_IMPLICIT_CONSTRUCTORS(Instr);
 };
 
 }  // namespace dart
 
 #endif  // VM_CONSTANTS_MIPS_H_