[ignition] Use more-targeted check for CONST-this-initialization hole check

This brings the BytecodeGenerator in line with FullCodeGenerator, now that
more requests for hole checks are flowing through BuildVariableAssignment.

BUG=chromium:658528

Review-Url: https://codereview.chromium.org/2447783002
Cr-Commit-Position: refs/heads/master@{#40557}

src/interpreter/bytecode-generator.cc

@@ -1945,17 +1945,16 @@ void BytecodeGenerator::BuildThrowIfNotHole(Handle<String> name) {
 
 void BytecodeGenerator::BuildHoleCheckForVariableAssignment(Variable* variable,
                                                             Token::Value op) {
-  if (op != Token::INIT) {
-    // Perform an initialization check for let/const declared variables.
-    // E.g. let x = (x = 20); is not allowed.
-    BuildThrowIfHole(variable->name());
-  } else {
-    DCHECK(variable->is_this() && variable->mode() == CONST &&
-           op == Token::INIT);
+  if (variable->is_this() && variable->mode() == CONST && op == Token::INIT) {
     // Perform an initialization check for 'this'. 'this' variable is the
     // only variable able to trigger bind operations outside the TDZ
     // via 'super' calls.
     BuildThrowIfNotHole(variable->name());
+  } else {
+    // Perform an initialization check for let/const declared variables.
+    // E.g. let x = (x = 20); is not allowed.
+    DCHECK(IsLexicalVariableMode(variable->mode()));
+    BuildThrowIfHole(variable->name());
   }
 }
 

test/mjsunit/regress/regress-crbug-658528.js

+// Copyright 2016 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.
+
+function f() {
+  eval("var x = 1");
+  const x = 2;
+}
+
+assertThrows(f, SyntaxError);