Support multi-byte nop instructions as recommended by

src/ia32/disasm-ia32.cc

 // Copyright 2011 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 969 matching lines @@
           }
         }
         break;
 
       case 0x81:  // fall through
       case 0x83:  // 0x81 with sign extension bit set
         data += PrintImmediateOp(data);
         break;
 
       case 0x0F:
-        { byte f0byte = *(data+1);
+        { byte f0byte = data[1];
           const char* f0mnem = F0Mnem(f0byte);
           if (f0byte == 0x18) {
             int mod, regop, rm;
             get_modrm(*data, &mod, &regop, &rm);
             const char* suffix[] = {"nta", "1", "2", "3"};
             AppendToBuffer("%s%s ", f0mnem, suffix[regop & 0x03]);
             data += PrintRightOperand(data);
+          } else if (f0byte == 0x1F && data[2] == 0) {
+            AppendToBuffer("nop");  // 3 byte nop.
+            data += 3;
+          } else if (f0byte == 0x1F && data[2] == 0x40 && data[3] == 0) {
+            AppendToBuffer("nop");  // 4 byte nop.
+            data += 4;
+          } else if (f0byte == 0x1F && data[2] == 0x44 && data[3] == 0 &&
+                     data[4] == 0) {
+            AppendToBuffer("nop");  // 5 byte nop.
+            data += 5;
+          } else if (f0byte == 0x1F && data[2] == 0x80 && data[3] == 0 &&
+                     data[4] == 0 && data[5] == 0 && data[6] == 0) {
+            AppendToBuffer("nop");  // 7 byte nop.
+            data += 7;
+          } else if (f0byte == 0x1F && data[2] == 0x84 && data[3] == 0 &&
+                     data[4] == 0 && data[5] == 0 && data[6] == 0 &&
+                     data[7] == 0) {
+            AppendToBuffer("nop");  // 8 byte nop.
+            data += 8;
           } else if (f0byte == 0xA2 || f0byte == 0x31) {
             AppendToBuffer("%s", f0mnem);
             data += 2;
           } else if (f0byte == 0x28) {
             data += 2;
             int mod, regop, rm;
             get_modrm(*data, &mod, &regop, &rm);
             AppendToBuffer("movaps %s,%s",
                            NameOfXMMRegister(regop),
                            NameOfXMMRegister(rm));
@@ skipping 115 matching lines @@
             AppendToBuffer(",%s", NameOfByteCPURegister(regop));
           } else {
             AppendToBuffer("%s ", "mov");
             data += PrintRightOperand(data);
             AppendToBuffer(",%s", NameOfCPURegister(regop));
           }
         }
         break;
 
       case 0x66:  // prefix
-        data++;
-        if (*data == 0x8B) {
+        while (*data == 0x66) data++;
+        if (*data == 0xf && data[1] == 0x1f) {
+          AppendToBuffer("nop");  // 0x66 prefix
+        } else if (*data == 0x90) {
+          AppendToBuffer("nop");  // 0x66 prefix
+        } else if (*data == 0x8B) {
           data++;
           data += PrintOperands("mov_w", REG_OPER_OP_ORDER, data);
         } else if (*data == 0x89) {
           data++;
           int mod, regop, rm;
           get_modrm(*data, &mod, &regop, &rm);
           AppendToBuffer("mov_w ");
           data += PrintRightOperand(data);
           AppendToBuffer(",%s", NameOfCPURegister(regop));
         } else if (*data == 0x0F) {
@@ skipping 106 matching lines @@
           } else if (*data == 0x70) {
             data++;
             int mod, regop, rm;
             get_modrm(*data, &mod, &regop, &rm);
             int8_t imm8 = static_cast<int8_t>(data[1]);
             AppendToBuffer("pshufd %s,%s,%d",
                            NameOfXMMRegister(regop),
                            NameOfXMMRegister(rm),
                            static_cast<int>(imm8));
             data += 2;
+          } else if (*data == 0x90) {
+            data++;
+            AppendToBuffer("nop");  // 2 byte nop.
           } else if (*data == 0xF3) {
             data++;
             int mod, regop, rm;
             get_modrm(*data, &mod, &regop, &rm);
             AppendToBuffer("psllq %s,%s",
                            NameOfXMMRegister(regop),
                            NameOfXMMRegister(rm));
             data++;
           } else if (*data == 0x73) {
             data++;
@@ skipping 378 matching lines @@
       fprintf(f, "  ");
     }
     fprintf(f, "  %s\n", buffer.start());
   }
 }
 
 
 }  // namespace disasm
 
 #endif  // V8_TARGET_ARCH_IA32