Bug 143247 – Object.preventExtensions/seal/freeze makes code much slower

• Component: JavaScriptCore
• Status: RESOLVED FIXED

[Elliott Sprehn]

If you have

class Foo {
  constructor() {
    this.property = 1;
    Object.preventExtensions(this);
  }
}

calling new Foo() seems to be 2-3x slower than doing so without the call to preventExtensions. This is not the case in v8 or Firefox. This pattern is really nice since it catches bad assignments and typos in code.

[Filip Pizlo]

Created attachment 283875 [details]
work in progress

[Filip Pizlo]

Created attachment 283877 [details]
the patch

[Filip Pizlo]

Created attachment 283878 [details]
the patch

The previous patch didn't include the LayoutTests additions.  I'm still testing this, but so far it appears to work like a charm.

[Filip Pizlo]

Comment on attachment 283878 [details]
the patch

I'm seeing crashes.  I'll put up a better patch once I figure out what those are all about.

[Build Bot]

Comment on attachment 283878 [details]
the patch

Attachment 283878 [details] did not pass mac-wk2-ews (mac-wk2):
Output: http://webkit-queues.webkit.org/results/1699149

New failing tests:
js/preventExtensions.html

[Build Bot]

Created attachment 283879 [details]
Archive of layout-test-results from ews106 for mac-yosemite-wk2

The attached test failures were seen while running run-webkit-tests on the mac-wk2-ews.
Bot: ews106  Port: mac-yosemite-wk2  Platform: Mac OS X 10.10.5

[Build Bot]

Comment on attachment 283878 [details]
the patch

Attachment 283878 [details] did not pass mac-debug-ews (mac):
Output: http://webkit-queues.webkit.org/results/1699142

New failing tests:
js/preventExtensions.html

[Build Bot]

Created attachment 283880 [details]
Archive of layout-test-results from ews114 for mac-yosemite

The attached test failures were seen while running run-webkit-tests on the mac-debug-ews.
Bot: ews114  Port: mac-yosemite  Platform: Mac OS X 10.10.5

[Filip Pizlo]

Created attachment 283882 [details]
the patch

Fixed the test failure.

[Filip Pizlo]

Created attachment 283883 [details]
performance

[Filip Pizlo]

Created attachment 283884 [details]
the patch

Included perf data.

[Michael Saboff]

Comment on attachment 283884 [details]
the patch

r=me

[Filip Pizlo]

Landed in https://trac.webkit.org/changeset/203368

[Keith Miller]

Looks like this breaks some test262 tests.

Specifically:

JSTests/test262/test/built-ins/Object/freeze/15.2.3.9-2-c-2.js
JSTests/test262/test/built-ins/Object/freeze/15.2.3.9-2-c-3.js
JSTests/test262/test/built-ins/Object/freeze/15.2.3.9-2-c-4.js

Which can be run with:

jsc JSTests/test262/harness/assert.js JSTests/test262/harness/sta.js JSTests/test262/harness/propertyHelper.js <testFile>

[Filip Pizlo]

(In reply to comment #14)
> Looks like this breaks some test262 tests.
> 
> Specifically:
> 
> JSTests/test262/test/built-ins/Object/freeze/15.2.3.9-2-c-2.js
> JSTests/test262/test/built-ins/Object/freeze/15.2.3.9-2-c-3.js
> JSTests/test262/test/built-ins/Object/freeze/15.2.3.9-2-c-4.js
> 
> Which can be run with:
> 
> jsc JSTests/test262/harness/assert.js JSTests/test262/harness/sta.js
> JSTests/test262/harness/propertyHelper.js <testFile>

Filed: https://bugs.webkit.org/show_bug.cgi?id=160479