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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri">The reason I chose this pass is that 1) what ‘isRevCopyChain’ does is mostly close with what this patch does, and 2) I didn’t realize that tied operand information can be used as a hint
to how two address instructions will be generated. I wonder if there’s a pass that builds recurrence cycle after instruction selection.<o:p></o:p></span></p>
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<p class="MsoNormal"><b><span style="font-family:Calibri;color:black">From: </span>
</b><span style="font-family:Calibri;color:black">Daniel Berlin <dberlin@dberlin.org><br>
<b>Date: </b>Friday, May 19, 2017 at 1:21 PM<br>
<b>To: </b>"reviews+D31821+public+c2af05dc8d0e9460@reviews.llvm.org" <reviews+D31821+public+c2af05dc8d0e9460@reviews.llvm.org>, Taewook Oh via Phabricator <reviews@reviews.llvm.org><br>
<b>Cc: </b>Taewook Oh <twoh@fb.com>, Quentin Colombet <qcolombet@apple.com>, Matthias Braun <matze@braunis.de>, Wei Mi <wmi@google.com>, llvm-commits <llvm-commits@lists.llvm.org><br>
<b>Subject: </b>Re: [PATCH] D31821: Remove redundant copy in recurrences<o:p></o:p></span></p>
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<p class="MsoNormal">The normal path to finding recurrences like this would be to follow def-use chains using an SCC algorithm, and then do something with the members of the component it comes up with.
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<p class="MsoNormal" style="margin-bottom:12.0pt">I presume you are doing something else because it's difficult to get that info at this point in the compiler?<o:p></o:p></p>
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<p class="MsoNormal">On Fri, May 19, 2017 at 1:14 PM, Taewook Oh via Phabricator via llvm-commits <<a href="mailto:llvm-commits@lists.llvm.org" target="_blank">llvm-commits@lists.llvm.org</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal">twoh added a comment.<br>
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@wmi Thank you for your reply. I agree on you that we should consider tied operand group, and as @qcolombet mentioned in the previous comment, if tie operand information is already available before this pass, I'd like to discuss where would be the best place
to implement this.<br>
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I'm afraid I couldn't understand your second point. In the example there is a recurrence cycle of vreg0-->vreg13-->vreg3-->vreg10-->vreg0 as well, and what this patch does is commuting (vreg0, vreg1) and (vreg2, vreg10) to remove the copy. Did I miss something?<o:p></o:p></p>
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<a href="https://urldefense.proofpoint.com/v2/url?u=https-3A__reviews.llvm.org_D31821&d=DwMFaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=kOsLCgQzH7N8ptZ7diJD9g&m=f0DRqqVS3FrUByhtpjTFwzMsMYlzLMlaZtdGgWQbqcA&s=RGxh4gMn7P80wd5i0rc1tg_EQ8iGVtj5DlhcFlH-OlQ&e=" target="_blank">https://reviews.llvm.org/D31821</a><br>
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