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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#44546A">I'm not aware of any additional bits needed. But putting us right at the edge leaves me uncomfortable. So an implementation that isn't limited by the 7 bits
in SubclassOptionalData seems sensible.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#44546A"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#44546A">Thanks,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#44546A">-Warren<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#44546A"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> Sanjay Patel [mailto:spatel@rotateright.com]
<br>
<b>Sent:</b> Monday, October 2, 2017 12:06 AM<br>
<b>To:</b> Ristow, Warren<br>
<b>Cc:</b> Hal Finkel; llvm-dev@lists.llvm.org<br>
<b>Subject:</b> Re: [llvm-dev] Trouble when suppressing a portion of fast-math-transformations<o:p></o:p></span></p>
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<p class="MsoNormal">Are we confident that we just need those 7 bits to represent all of the relaxed FP states that we need/want to support?
<o:p></o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt">I'm asking because FMF in IR is currently mapped onto the SubclassOptionalData of Value...and we have exactly 7 bits there. :)<o:p></o:p></p>
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<p class="MsoNormal">If we're redoing the definitions, I'm wondering if we can share the struct with the backend's SDNodeFlags, but that already has one extra bit for vector reduction. Should we give up on SubclassOptionalData for FMF? We have a MD_fpmath enum
value for metadata, so we could move things over there?<o:p></o:p></p>
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<p class="MsoNormal">On Fri, Sep 29, 2017 at 8:16 PM, Ristow, Warren via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org" target="_blank">llvm-dev@lists.llvm.org</a>> wrote:<o:p></o:p></p>
<p class="MsoNormal">Hi Hal,<br>
<br>
>> 4. To fix this, I think that additional fast-math-flags are likely<br>
>> needed in the IR. Instead of the following set:<br>
>><br>
>> 'nnan' + 'ninf' + 'nsz' + 'arcp' + 'contract'<br>
>><br>
>> something like this:<br>
>><br>
>> 'reassoc' + 'libm' + 'nnan' + 'ninf' + 'nsz' + 'arcp' + 'contract'<br>
>><br>
>> would be more useful. Related to this, the current 'fast' flag which acts<br>
>> as an umbrella (enabling 'nnan' + 'ninf' + 'nsz' + 'arcp' + 'contract') may<br>
>> not be needed. A discussion on this point was raised last November on the<br>
>> mailing list:<br>
>><br>
>> <a href="http://lists.llvm.org/pipermail/llvm-dev/2016-November/107104.html" target="_blank">
http://lists.llvm.org/pipermail/llvm-dev/2016-November/107104.html</a><br>
><br>
> I agree. I'm happy to help review the patches. It will be best to have<br>
> only the finer-grained flags where there's no "fast" flag that implies<br>
> all of the others.<br>
<br>
Thanks for the quick response, and for the willingness to review. I won't let<br>
this languish so long, like the post from last November.<br>
<br>
Happy to hear that you feel it's best not to have the umbrella "fast" flag.<br>
<br>
Thanks again,<o:p></o:p></p>
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<p class="MsoNormal">-Warren<br>
_______________________________________________<br>
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<a href="http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev" target="_blank">http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev</a><o:p></o:p></p>
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