Support dec_b instruction in ia32 and x64 disassembler.

src/x64/disasm-x64.cc

 // Copyright 2009 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 1432 matching lines @@
                          NameOfCPURegister(reg));
         }
         data++;
       }
         break;
 
       case 0xFE: {
         data++;
         int mod, regop, rm;
         get_modrm(*data, &mod, &regop, &rm);
-        if (mod == 3 && regop == 1) {
-          AppendToBuffer("decb %s", NameOfCPURegister(rm));
+        if (regop == 1) {
+          AppendToBuffer("decb ");
+          data += PrintRightOperand(data);
         } else {
           UnimplementedInstruction();
         }
-        data++;
       }
         break;
 
       case 0x68:
         AppendToBuffer("push 0x%x", *reinterpret_cast<int32_t*>(data + 1));
         data += 5;
         break;
 
       case 0x6A:
         AppendToBuffer("push 0x%x", *reinterpret_cast<int8_t*>(data + 1));
@@ skipping 218 matching lines @@
     for (int i = 6 - static_cast<int>(pc - prev_pc); i >= 0; i--) {
       fprintf(f, "  ");
     }
     fprintf(f, "  %s\n", buffer.start());
   }
 }
 
 }  // namespace disasm
 
 #endif  // V8_TARGET_ARCH_X64