<div dir="ltr">I suspect the most direct resolution here is to see the problem directly. Can you post a patch?<div><br></div><div>-Nirav</div></div><div class="gmail_extra"><br><div class="gmail_quote">On Mon, May 22, 2017 at 3:01 PM, Amaury SECHET <span dir="ltr"><<a href="mailto:deadalnix@gmail.com" target="_blank">deadalnix@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">Explicitly re-adding a node to be processed doesn't work, because the processing order is canonical.<br></div><div class="HOEnZb"><div class="h5"><div class="gmail_extra"><br><div class="gmail_quote">2017-05-22 11:39 GMT-07:00 Nirav Davé <span dir="ltr"><<a href="mailto:niravd@google.com" target="_blank">niravd@google.com</a>></span>:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div>You can always explicitly add D to the worklist when you make the transformation with AddToWorklist. Presuambly this was the cause for your infinite loop. </div><span class="m_5726172412694635288HOEnZb"><font color="#888888"><div><br></div><div>-Nirav</div><div><br></div></font></span></div><div class="m_5726172412694635288HOEnZb"><div class="m_5726172412694635288h5"><div class="gmail_extra"><br><div class="gmail_quote">On Mon, May 22, 2017 at 2:07 PM, Amaury SECHET <span dir="ltr"><<a href="mailto:deadalnix@gmail.com" target="_blank">deadalnix@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div>The root problem is that, when A gets modified, D doesn't get added back to the worklist. I could match the pattern on A, but the problem remains: when D gets modified, A do not get added back tot he worklist.<br><br></div><div>I also considered ding several round of DAGCombine, but it is very easy to run into infinite loops, even with a fair amount of sanity checks.<br></div></div><div class="m_5726172412694635288m_8942244940396829307HOEnZb"><div class="m_5726172412694635288m_8942244940396829307h5"><div class="gmail_extra"><br><div class="gmail_quote">2017-05-22 7:30 GMT-07:00 Nirav Davé <span dir="ltr"><<a href="mailto:niravd@google.com" target="_blank">niravd@google.com</a>></span>:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div>This is a little hard to diagnose in the abstract, but it sounds like you're having a loop along the lines of visit A -> visit B/C -> visit D -> visit A and that at each step you're making a real reasonable change to the DAG and returning to the original DAG. <br></div><div><br></div><div>One possible solution is to to rework the optimization to occur when visiting A not D. so the last edge in the visit loop no longer happens. <br></div><div><br></div><div>If that's not feasible, I don't think there's much you can do that is not effectively preventing one of those transitions from occurring when it would cause the infinite visit loop.</div><div><br></div><div>HTH,</div><div><br></div><div>-Nirav</div><div><br></div><div></div></div><div class="gmail_extra"><br><div class="gmail_quote"><div><div class="m_5726172412694635288m_8942244940396829307m_-7887468062375878803h5">On Mon, May 22, 2017 at 2:21 AM, Amaury SECHET via llvm-dev <span dir="ltr"><<a href="mailto:llvm-dev@lists.llvm.org" target="_blank">llvm-dev@lists.llvm.org</a>></span> wrote:<br></div></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><div class="m_5726172412694635288m_8942244940396829307m_-7887468062375878803h5"><div dir="ltr"><div><div><div><div><div><span style="font-family:monospace,monospace">I'm trying to optimize a pattern that goes roughly as:<br></span></div><span style="font-family:monospace,monospace"> A<br> / \<br></span></div><span style="font-family:monospace,monospace"> B C<br> \ /<br></span></div><span style="font-family:monospace,monospace"> D<br><br></span></div><span style="font-family:monospace,monospace">Problem is, when A gets modified, B and C get added back to the worklist, but D doesn't. Readding D to the worklist just create an infinite loop where one process D again and again.<br><br></span></div><span style="font-family:monospace,monospace">Is there a proper way to make this work ?<br></span></div>
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