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<p class="MsoNormal"><span style="font-family:"Courier New";color:#44546A">It might be a useful experiment (changing FSub to emit an FNeg as appropriate) at least to see how many tests fail and how they fail. It looks like a ton of tests use fsub -0.0.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New";color:#44546A"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Courier New";color:#44546A">--</span><span style="color:#44546A">
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</span><span style="font-size:10.0pt;font-family:"Courier New";color:#44546A">Kevin P. Neal</span><span style="color:#44546A"><br>
</span><span style="font-size:10.0pt;font-family:"Courier New";color:#44546A">SAS/C and SAS/C++ Compiler<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Courier New";color:#44546A">Host Research and Development<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Courier New";color:#44546A">SAS Institute, Inc.</span><span style="color:#44546A"><o:p></o:p></span></p>
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<p class="MsoNormal"><b>From:</b> Cameron McInally <cameron.mcinally@nyu.edu> <br>
<b>Sent:</b> Tuesday, May 07, 2019 2:20 PM<br>
<b>To:</b> Sanjay Patel <spatel@rotateright.com><br>
<b>Cc:</b> Kevin Neal <Kevin.Neal@sas.com>; Matthew.Arsenault@amd.com; andrew.kaylor@intel.com; mcrosier@codeaurora.org; wei.ding2@amd.com; hiraditya@msn.com; llvm-commits@lists.llvm.org; jun.l@samsung.com<br>
<b>Subject:</b> Re: [PATCH] D61604: [InstCombine] sink FP negation of operands through select<o:p></o:p></p>
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<p><b><i><span style="font-size:12.0pt;font-family:"Arial",sans-serif;color:red">EXTERNAL</span></i></b><span style="font-size:12.0pt;font-family:"Arial",sans-serif;color:red">
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<p class="MsoNormal">On Tue, May 7, 2019 at 11:44 AM Sanjay Patel <<a href="mailto:spatel@rotateright.com">spatel@rotateright.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal">On Tue, May 7, 2019 at 7:16 AM Kevin Neal <<a href="mailto:Kevin.Neal@sas.com" target="_blank">Kevin.Neal@sas.com</a>> wrote:<o:p></o:p></p>
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How should we handle regressions in code quality that are exposed by tests?<o:p></o:p></p>
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<p class="MsoNormal">One idea I had (or I may be remembering someone else's suggestion) was to grep the existing IR regression tests for 'fsub -0.0', then create a sibling test using fneg. If that doesn't result in the same output, then we need to do some pattern
matching enhancement.<o:p></o:p></p>
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<p class="MsoNormal">I'm not opposed to this, but it does sound like a ton of work.
<o:p></o:p></p>
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<p class="MsoNormal">What if we checked for a -0.0 constant in IRBuilder::FSub*(...) and created an FNeg instead? Then we should only see test changes with `fsub -0.0`-> `fneg`. If we find anything else, it would need a closer look. Does that miss anything?<o:p></o:p></p>
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