[Webkit-unassigned] [Bug 173407] WTF::StringImpl::copyChars segfaults when built with GCC 7

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=173407

--- Comment #10 from Yusuke Suzuki <utatane.tea at gmail.com> ---
(In reply to Yusuke Suzuki from comment #9)
> (In reply to Konstantin Tokarev from comment #8)
> > For the record, optimization that avoids memcpy was initially added by Darin
> > in https://bugs.webkit.org/show_bug.cgi?id=20671 (2008)
> 
> OK, that note is very helpful because it clarifies that this optimization is
> driven by SunSpider.

I've just tested it on my Linux box.

VMs tested:
"baseline" at /home/yusukesuzuki/dev/WebKit/WebKitBuild/string-copy-tot/Release/bin/jsc
"patched" at /home/yusukesuzuki/dev/WebKit/WebKitBuild/string-copy/Release/bin/jsc

Collected 100 samples per benchmark/VM, with 100 VM invocations per benchmark. Emitted a call to gc()
between sample measurements. Used 1 benchmark iteration per VM invocation for warm-up. Used the
jsc-specific preciseTime() function to get microsecond-level timing. Reporting benchmark execution
times with 95% confidence intervals in milliseconds.

                                baseline                  patched                                      

string-base64                7.7544+-0.1761            7.6138+-0.2071          might be 1.0185x faster
string-fasta                10.5429+-0.2746     ?     10.7500+-0.2669        ? might be 1.0196x slower
string-tagcloud             14.8588+-0.2828           14.8039+-0.3039        
string-unpack-code          36.1769+-0.4251           35.3397+-0.5398          might be 1.0237x faster
string-validate-input        8.5182+-0.2206            8.3514+-0.2179          might be 1.0200x faster

<arithmetic>                15.5702+-0.1239           15.3718+-0.1452          might be 1.0129x faster


It seems there is no explicit difference right now. The compiler is GCC 5.4.0
I would like to see the difference in macOS's clang.

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