VM: Improve and fix double negation on MIPS.

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 744 matching lines @@
   }
 
   void mult(Register rs, Register rt) {
     EmitRType(SPECIAL, rs, rt, R0, 0, MULT);
   }
 
   void multu(Register rs, Register rt) {
     EmitRType(SPECIAL, rs, rt, R0, 0, MULTU);
   }
 
+  void negd(DRegister dd, DRegister ds) {
+    FRegister fd = static_cast<FRegister>(dd * 2);
+    FRegister fs = static_cast<FRegister>(ds * 2);
+    EmitFpuRType(COP1, FMT_D, F0, fs, fd, COP1_NEG);
+  }
+
   void nop() {
     Emit(Instr::kNopInstruction);
   }
 
   void nor(Register rd, Register rs, Register rt) {
     EmitRType(SPECIAL, rs, rt, rd, 0, NOR);
   }
 
   void or_(Register rd, Register rs, Register rt) {
     EmitRType(SPECIAL, rs, rt, rd, 0, OR);
@@ skipping 970 matching lines @@
                                   Register value,
                                   Label* no_update);
 
   DISALLOW_ALLOCATION();
   DISALLOW_COPY_AND_ASSIGN(Assembler);
 };
 
 }  // namespace dart
 
 #endif  // VM_ASSEMBLER_MIPS_H_