Bug 150034

Summary:

"A + B" with strings shouldn't copy if A or B is empty.

Product:

WebKit

Reporter:

Andreas Kling <kling>

Component:

Web Template Framework

Assignee:

Andreas Kling <kling>

Status:

RESOLVED FIXED

Severity:

Normal

CC:

benjamin, cmarcelo, commit-queue, keith_miller, kling

Priority:

Keywords:

Performance

Version:

WebKit Nightly Build

Hardware:

Unspecified

OS:

Unspecified

Attachments:

Description	Flags
Patch	none

Description Andreas Kling 2015-10-12 10:45:59 PDT

Doing A + B where A and B are string types will currently always allocate a new StringImpl C with length A.length+B.length, and then blit the contents of A and B into C.
We should have a fast path for A + B where A.length == 0 || B.length == 0.

Comment 1 Andreas Kling 2015-10-12 10:50:45 PDT

Created attachment 262899 [details]
Patch

Comment 2 WebKit Commit Bot 2015-10-12 12:45:27 PDT

Comment on attachment 262899 [details]
Patch

Clearing flags on attachment: 262899

Committed r190882: <http://trac.webkit.org/changeset/190882>

Comment 3 WebKit Commit Bot 2015-10-12 12:45:30 PDT

All reviewed patches have been landed.  Closing bug.

Comment 4 Keith Miller 2015-10-14 07:02:57 PDT

It looks like this patch is breaking the jsc command line REPL. If you try:

DYLD_FRAMEWORK_PATH=Safari-Gala-Production-SafariTen-190882-76008.app/Contents/Frameworks ./Safari-Gala-Production-SafariTen-190882-76008.app/Contents/Resources/jsc
>>> foo = 1
Exception: ReferenceError: Can't find variable: f

Comment 5 Andreas Kling 2015-10-14 09:23:50 PDT

(In reply to comment #4)
> It looks like this patch is breaking the jsc command line REPL. If you try:
> 
> DYLD_FRAMEWORK_PATH=Safari-Gala-Production-SafariTen-190882-76008.app/
> Contents/Frameworks
> ./Safari-Gala-Production-SafariTen-190882-76008.app/Contents/Resources/jsc
> >>> foo = 1
> Exception: ReferenceError: Can't find variable: f

Oh dang! I see what the bug is: StringTypeAdapter<const UChar*>::toString() always uses length=1 instead of the provided character count.

Crazy that no test caught this. Will fix shortly.