<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
</head>
<body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">
[ +CC Davide, who’s been fixing these unreachable block bugs]
<div class=""><br class="">
</div>
<div class="">Hi Serguei, </div>
<div class=""><br class="">
</div>
<div class="">I think loop deletion needs to be fixed here.</div>
<div class=""><br class="">
</div>
<div class="">For LCSSA verification in `isBlockInLCSSAForm`, we specifically ignore uses in blocks that are not reachable from entry.</div>
<div class="">
<div class="">We do not need phis for such uses.</div>
</div>
<div class=""><br class="">
</div>
<div class="">
<div class="">So, a loop can be in LCSSA form and still have unreachable uses for def’s and not have phis for those defs.</div>
</div>
<div class=""><br class="">
</div>
<div class="">Although loop deletion uses a reasonable (and AFAICT correct) logic for identifying “invariant” loops by depending on the fact that LCSSA is preserved.</div>
<div class="">it needs to take into account unreachable uses before deleting that invariant loop.</div>
<div class=""><br class="">
</div>
<div class="">
<div class=""><br class="">
</div>
</div>
<div class=""><br class="">
</div>
<div class="">Anna</div>
<div class=""><br class="">
</div>
<div class=""><br class="">
<div>
<blockquote type="cite" class="">
<div class="">On Jan 10, 2018, at 4:00 AM, Serguei Katkov via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org" class="">llvm-dev@lists.llvm.org</a>> wrote:</div>
<br class="Apple-interchange-newline">
<div class="">
<div class="WordSection1" style="page: WordSection1; font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;">
<div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">
Hello All,<o:p class=""></o:p></div>
<div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">
<o:p class=""> </o:p></div>
<div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">
I filed a bug<span class="Apple-converted-space"> </span><a href="https://bugs.llvm.org/show_bug.cgi?id=35884" style="color: rgb(149, 79, 114); text-decoration: underline;" class="">https://bugs.llvm.org/show_bug.cgi?id=35884</a><span class="Apple-converted-space"> </span>which
I want to fix but I'm in trouble with detecting who is wrong :)<o:p class=""></o:p></div>
<div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">
<o:p class=""> </o:p></div>
<div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">
The story is as follows:<o:p class=""></o:p></div>
<div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">
LoopDeletion tries to delete an invariant loop which has a def with use in some unreachable block.<o:p class=""></o:p></div>
<div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">
The IR is well-formed due to any use in unreachable block is dominated as Verifier states.<o:p class=""></o:p></div>
<div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">
<o:p class=""> </o:p></div>
<div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">
LoopDeletion detected the loop as invariant due to LCSSA builder did not create a Phi node for this def because this def is in<o:p class=""></o:p></div>
<div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">
block which does not dominate exit.<o:p class=""></o:p></div>
<div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">
<o:p class=""> </o:p></div>
<div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">
When BB with def is destroyed the destroying of def instruction causes an assert due to it has use.<o:p class=""></o:p></div>
<div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">
<o:p class=""> </o:p></div>
<div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">
So I wonder who is wrong here:<o:p class=""></o:p></div>
<div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">
1) LCSSA which did not create a Phi node<o:p class=""></o:p></div>
<div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">
2) LoopDeletion which did not take into account that instruction can be used in unreachable block and used a bulk deletion.<o:p class=""></o:p></div>
<div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">
<o:p class=""> </o:p></div>
<div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">
Any help is appreciated.<o:p class=""></o:p></div>
<div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">
<span lang="RU" class=""><o:p class=""> </o:p></span></div>
<div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">
Thank you,<o:p class=""></o:p></div>
<div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">
Serguei.<o:p class=""></o:p></div>
<div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">
<span lang="RU" class=""><o:p class=""> </o:p></span></div>
</div>
<span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class="">_______________________________________________</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class="">
<span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class="">LLVM
Developers mailing list</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class="">
<a href="mailto:llvm-dev@lists.llvm.org" style="color: rgb(149, 79, 114); text-decoration: underline; font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px;" class="">llvm-dev@lists.llvm.org</a><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class="">
<a href="http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev" style="color: rgb(149, 79, 114); text-decoration: underline; font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px;" class="">http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev</a></div>
</blockquote>
</div>
<br class="">
</div>
</body>
</html>