Merged: Turn off in-place field representation changes

Revision: 3ce92ce8499a512e15c8ee26c83e4c2c27e3b056

BUG=chromium:952682
LOG=N
NOTRY=true
NOPRESUBMIT=true
NOTREECHECKS=true
R=bmeurer@chromium.org

Change-Id: I42907c53d6d227c37af43408b341d675c84181e2
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1598752
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/branch-heads/7.5@{#24}
Cr-Branched-From: 35b9bf5-refs/heads/7.5.288@{#1}
Cr-Branched-From: 912b391-refs/heads/master@{#60911}

src/flag-definitions.h

@@ -1048,7 +1048,7 @@ DEFINE_BOOL_READONLY(track_constant_fields, true,
                      "enable constant field tracking")
 DEFINE_BOOL_READONLY(fast_map_update, false,
                      "enable fast map update by caching the migration target")
-DEFINE_BOOL(modify_field_representation_inplace, true,
+DEFINE_BOOL(modify_field_representation_inplace, false,
             "enable in-place field representation updates")
 DEFINE_INT(max_polymorphic_map_count, 4,
            "maximum number of maps to track in POLYMORPHIC state")

test/mjsunit/regress-952682.js

@@ -0,0 +1,15 @@
+// Copyright 2019 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: --allow-natives-syntax
+
+function f(array, x) {
+  array.x = x;
+  array[0] = undefined;
+  return array;
+}
+
+f([1], 1);
+f([2], 1);
+%HeapObjectVerify(f([3], undefined));