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<p class="MsoNormal">Hi everyone,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I’ve been exploring clang’s fp-contract behavior recently, and I see that when ‘-ffp-contract=fast’ is used it can’t be overridden with a pragma. I would have regarded this as a bug (and in fact, a bug has been filed
<a href="https://bugs.llvm.org/show_bug.cgi?id=39679">https://bugs.llvm.org/show_bug.cgi?id=39679</a>). However, I’ve found some discussions on the mailing lists that described this as expected behavior.<o:p></o:p></p>
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<p class="MsoNormal">Last October, Sam Liu added support for a new setting (‘fp-contract=fast-honor-pragmas’) and updated the clang documentation to reflect the behavior of fp-contract=fast. See
<a href="https://reviews.llvm.org/D90174">https://reviews.llvm.org/D90174</a>. I feel very strongly that this should have been done the other way around -- fp-contract=fast should honor pragmas and if we need an option that doesn’t that could be added.<o:p></o:p></p>
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<p class="MsoNormal">In the above review, John McCall asked what “other compilers” do. Steve Canon showed that GCC doesn’t honor the pragma. If I may humbly offer another “other compiler”, ICC (which doesn’t distinguish between ‘on’ and ‘fast’ for fp-contract)
does respect the pragma (<a href="https://godbolt.org/z/x5r9WdYb4">https://godbolt.org/z/x5r9WdYb4</a>). I’m not saying that ICC should be treated as a reference implementation over GCC or anything like that, but I am saying that its behavior strikes me as
more correct than what GCC or clang currently do.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thoughts and opinions?<o:p></o:p></p>
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<p class="MsoNormal">Thanks,<o:p></o:p></p>
<p class="MsoNormal">Andy<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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