Bug 68294 – method_check should repatch itself if it finds that the new structure(s) are the result of transitions from the old structure(s)

• Status: RESOLVED
• Resolution: FIXED
• Component: JavaScriptCore

[Filip Pizlo]

The method_check optimization in the old JIT is now relied upon as a kind of profiling by the DFG JIT.  But this fails if the method_check takes the slow path simply because the structures it was caching on were transitioned.  This results in missed dead code elimination and inlining opportunities in the DFG.

The old JIT should simply repatch the fast path of method_check if it finds that the slow path was taken only because of structure transitions, but that the specific function optimization for that property is otherwise intact.

[Filip Pizlo]

Created attachment 107749 [details]
the patch

[WebKit Review Bot]

Attachment 107749 [details] did not pass style-queue:

Failed to run "['Tools/Scripts/check-webkit-style', '--diff-files', u'Source/JavaScriptCore/ChangeLog', u'Source..." exit_code: 1

Source/JavaScriptCore/jit/JITStubs.cpp:1634:  Should have only a single space after a punctuation in a comment.  [whitespace/comments] [5]
Source/JavaScriptCore/jit/JITStubs.cpp:1644:  Should have only a single space after a punctuation in a comment.  [whitespace/comments] [5]
Source/JavaScriptCore/jit/JITStubs.cpp:1645:  Should have only a single space after a punctuation in a comment.  [whitespace/comments] [5]
Source/JavaScriptCore/jit/JITStubs.cpp:1646:  Should have only a single space after a punctuation in a comment.  [whitespace/comments] [5]
Total errors found: 4 in 5 files


If any of these errors are false positives, please file a bug against check-webkit-style.

[Filip Pizlo]

Created attachment 107751 [details]
the patch

[Filip Pizlo]

Landed in r95388.