MIPS: Fix compilation failures due to warnings on mips32r1

test/cctest/test-assembler-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 5440 matching lines @@
   const size_t kTableLength = sizeof(test_cases) / sizeof(TestCaseMaddMsub<T>);
   TestCaseMaddMsub<T> tc;
   for (size_t i = 0; i < kTableLength; i++) {
     tc.fr = test_cases[i].fr;
     tc.fs = test_cases[i].fs;
     tc.ft = test_cases[i].ft;
 
     (CALL_GENERATED_CODE(isolate, f, &tc, 0, 0, 0, 0));
 
     T res_add = tc.fr + (tc.fs * tc.ft);
-    T res_sub;
+    T res_sub = 0;
     if (IsMipsArchVariant(kMips32r2)) {
       res_sub = (tc.fs * tc.ft) - tc.fr;
     } else if (IsMipsArchVariant(kMips32r6)) {
       res_sub = tc.fr - (tc.fs * tc.ft);
+    } else {
+      UNREACHABLE();
     }
 
     CHECK_EQ(tc.fd_add, res_add);
     CHECK_EQ(tc.fd_sub, res_sub);
   }
 }
 
 TEST(madd_msub_s) {
   if (!IsMipsArchVariant(kMips32r2)) return;
   helper_madd_msub_maddf_msubf<float>([](MacroAssembler& assm) {
@@ skipping 28 matching lines @@
   if (!IsMipsArchVariant(kMips32r6)) return;
   helper_madd_msub_maddf_msubf<double>([](MacroAssembler& assm) {
     __ maddf_d(f4, f6, f8);
     __ sdc1(f4, MemOperand(a0, offsetof(TestCaseMaddMsub<double>, fd_add)));
     __ msubf_d(f16, f6, f8);
     __ sdc1(f16, MemOperand(a0, offsetof(TestCaseMaddMsub<double>, fd_sub)));
   });
 }
 
 #undef __