[disassembler] Fix unimplemented instruction

After appending 'unimplemented instruction' we need to increase the data
pointer to avoid an endless loop and to fulfill a later DCHECK.

R=jkummerow@chromium.org

Bug: chromium:1201114
Change-Id: I707809f81a4d9a6b3653b94b4836482c006b76ad
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2843819Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74108}

src/diagnostics/ia32/disasm-ia32.cc

@@ -368,7 +368,7 @@ class DisassemblerIA32 {
         Disassembler::kAbortOnUnimplementedOpcode) {
       FATAL("Unimplemented instruction in disassembler");
     } else {
-      AppendToBuffer("'Unimplemented Instruction'");
+      AppendToBuffer("'Unimplemented instruction'");
     }
   }
 };
@@ -2076,6 +2076,7 @@ int DisassemblerIA32::InstructionDecode(v8::internal::Vector<char> out_buffer,
           data += 3;
         } else {
           UnimplementedInstruction();
+          data += 1;
         }
       } break;
 

test/mjsunit/regress/regress-1201114.js

+// Copyright 2021 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.
+
+// Flags: --turboprop --allow-natives-syntax --print-code
+
+var a = {b: 1};
+function nop() { return false; }
+function __f_4(a) { return a; }
+function __f_5(__v_2) {
+  __f_4(__v_2.a);
+  nop(__f_5)&a.b;
+}
+%PrepareFunctionForOptimization(__f_5);
+__f_5(true);
+%OptimizeFunctionOnNextCall(__f_5);
+try {
+  __f_5();
+} catch {}