MIPS: Fix several bugs that cause crashes in soft-float mode.

src/mips/code-stubs-mips.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 3112 matching lines @@
           __ Cvt_d_uw(double_scratch, double_scratch, single_scratch);
         }
 
         // Store the result.
         __ mov(v0, heap_number_result);
         __ sdc1(double_scratch, FieldMemOperand(v0, HeapNumber::kValueOffset));
         __ Ret();
       } else {
         // Tail call that writes the int32 in a2 to the heap number in v0, using
         // a3 and a0 as scratch. v0 is preserved and returned.
-        __ mov(a0, t1);
+        __ mov(v0, t1);
         WriteInt32ToHeapNumberStub stub(a2, v0, a3, a0);
         __ TailCallStub(&stub);
       }
 
       break;
     }
 
     default:
       UNREACHABLE();
   }
@@ skipping 4530 matching lines @@
   __ Ret(USE_DELAY_SLOT);
   __ mov(v0, a0);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_MIPS