[Webkit-unassigned] [Bug 232951] Prevent fused multiply add during ParseInt

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=232951

--- Comment #8 from Mikhail R. Gadelha <mikhail at igalia.com> ---
(In reply to Yusuke Suzuki from comment #7)
> Comment on attachment 443839 [details]
> Patch
> 
> View in context:
> https://bugs.webkit.org/attachment.cgi?id=443839&action=review
> 
> > Source/JavaScriptCore/runtime/ParseInt.h:113
> > +// Due to a GCC bug found in v8.4.0, a wrong fused multiply-add optimization can be inserted when calculating the final number,
> > +// in number *= radix; number += digit;, so optimizations are disabled for this functions.
> > +#pragma GCC push_options
> > +#pragma GCC optimize ("O0")
> 
> 1. Why not only disabling fp-contract? We do not need to disable all
> optimizations. (See comment
> https://bugs.webkit.org/show_bug.cgi?id=232951#c5)
> 2. Why not using function attribute?

I just tried adding `__attribute__((optimize("fp-contract=off")))` locally to the function definition and gcc seems to ignore it, i.e., it generates de fma and the test fails.

> 3. Use it only for GCC. Clang does not need this.

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