MIPS64: Fix code generator and simulator for DEXTM.

src/compiler/mips64/code-generator-mips64.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/compiler/code-generator.h"
 #include "src/compilation-info.h"
 #include "src/compiler/code-generator-impl.h"
 #include "src/compiler/gap-resolver.h"
 #include "src/compiler/node-matchers.h"
 #include "src/compiler/osr.h"
@@ skipping 1203 matching lines @@
         __ Ins(i.OutputRegister(), i.InputRegister(0), i.InputInt8(1),
                i.InputInt8(2));
       }
       break;
     case kMips64Dext: {
       int16_t pos = i.InputInt8(1);
       int16_t size = i.InputInt8(2);
       if (size > 0 && size <= 32 && pos >= 0 && pos < 32) {
         __ Dext(i.OutputRegister(), i.InputRegister(0), i.InputInt8(1),
                 i.InputInt8(2));
-      } else if (size > 32 && size <= 64 && pos > 0 && pos < 32) {
+      } else if (size > 32 && size <= 64 && pos >= 0 && pos < 32) {
         __ Dextm(i.OutputRegister(), i.InputRegister(0), i.InputInt8(1),
                  i.InputInt8(2));
       } else {
         DCHECK(size > 0 && size <= 32 && pos >= 32 && pos < 64);
         __ Dextu(i.OutputRegister(), i.InputRegister(0), i.InputInt8(1),
                  i.InputInt8(2));
       }
       break;
     }
     case kMips64Dins:
@@ skipping 1456 matching lines @@
       padding_size -= v8::internal::Assembler::kInstrSize;
     }
   }
 }
 
 #undef __
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8