Adds macros to the MIPS assembler for detecting overflow.

runtime/vm/assembler_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_ASSEMBLER_MIPS_H_
 #define VM_ASSEMBLER_MIPS_H_
 
 #ifndef VM_ASSEMBLER_H_
 #error Do not include assembler_mips.h directly; use assembler.h instead.
 #endif
@@ skipping 488 matching lines @@
   void sw(Register rt, const Address& addr) {
     EmitLoadStore(SW, rt, addr);
   }
 
   void xor_(Register rd, Register rs, Register rt) {
     EmitRType(SPECIAL, rs, rt, rd, 0, XOR);
   }
 
   // Macros in alphabetical order.
 
+  // Addition of rs and rt with the result placed in rd.
+  // After, ro < 0 if there was signed overflow, ro >= 0 otherwise.
+  // Clobbers TMP.

[regis, 2013/04/06 00:33:24]

By definition, TMP can be clobbered by any asm macro.
You should add a more detailed comment about register usage, otherwise the
caller will waste a register.
You should explain when a scratch register is required and when not.

[zra, 2013/04/08 16:45:25]

Done.

+  void AdduDetectOverflow(Register rd, Register rs, Register rt, Register ro,
+                          Register scratch);
+
   void Branch(const ExternalLabel* label) {
     LoadImmediate(TMP, label->address());
     jr(TMP);
   }
 
   void BranchPatchable(const ExternalLabel* label) {
     const uint16_t low = Utils::Low16Bits(label->address());
     const uint16_t high = Utils::High16Bits(label->address());
     lui(TMP, Immediate(high));
     ori(TMP, TMP, Immediate(low));
@@ skipping 210 matching lines @@
     delay_slot_available_ = true;
   }
 
   DISALLOW_ALLOCATION();
   DISALLOW_COPY_AND_ASSIGN(Assembler);
 };
 
 }  // namespace dart
 
 #endif  // VM_ASSEMBLER_MIPS_H_