<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><br class=""><div><br class=""><blockquote type="cite" class=""><div class="">On Oct 21, 2018, at 2:48 PM, mbraun 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=""><meta http-equiv="Content-Type" content="text/html; charset=utf-8" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">As far as I understand it (though I didn’t write the code so I may be missing something) this is about making sure liveness flags (kill, dead) are updated correctly when merging instruction. The situations to consider are probably:<div class=""><br class=""></div><div class="">1)</div><div class="">OP_X …, implicit-def %X</div><div class="">with</div><div class="">OP_X …, implicit-def dead %X</div><div class=""><br class=""></div><div class="">The merged instruction probably should not have a dead flag set. The 2nd if appears to be about this situation:</div><div class=""><br class=""></div><div class=""><br class=""></div><div class="">2)</div><div class="">OP_X …, implicit-def dead %X</div><div class="">Use killed %X</div><div class="">…</div><div class="">OP_X …, implicit-def %X ; this gets merged with the previous OP_X</div><div class="">Use %X</div></div></div></blockquote><div>This example should of course read:</div><div><br class=""></div><div>OP_X …, implicit-def %X</div><div>Use killed %X</div><div>…</div><div>OP_X …, implicit-def %X ; this gets merged with the previous OP_X</div><div>Use %X</div><div><br class=""></div><div>Once we merge the 2nd OP_X with the first one, we have to drop the `killed` flags on all users of %X between the first OP_X and the position where we had the 2nd OP_X before it was merged.</div><br class=""><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div class=""><br class=""></div><div class="">Once we merge the 2nd OP_X with the first one, we have to drop the `killed` flags on the %X users.</div><div class=""><br class=""></div><div class=""><br class=""></div><div class=""><br class=""></div><div class="">Though admittedly I am at a loss right now why this is only performed for implicit operands and not for all operands…</div><div class=""><br class=""></div><div class="">- Matthias</div><div class=""><div class=""><div class=""><br class=""><blockquote type="cite" class=""><div class="">On Oct 20, 2018, at 1:38 AM, Yuchao (Michael) 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; caret-color: rgb(0, 0, 0); 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; text-decoration: none;"><div style="margin: 0cm 0cm 0.0001pt; text-align: justify; font-size: 10.5pt; font-family: Calibri, sans-serif;" class=""><span lang="EN-US" class="">Hi<span class="Apple-converted-space"> </span><o:p class=""></o:p></span></div><div style="margin: 0cm 0cm 0.0001pt; text-align: justify; font-size: 10.5pt; font-family: Calibri, sans-serif;" class=""><span lang="EN-US" class=""><o:p class=""> </o:p></span></div><div style="margin: 0cm 0cm 0.0001pt; text-align: justify; font-size: 10.5pt; font-family: Calibri, sans-serif;" class=""><span lang="EN-US" class="">I am trying to fix a bug in MachineCSE and have one question about following code:<o:p class=""></o:p></span></div><div style="margin: 0cm 0cm 0.0001pt; text-align: justify; font-size: 10.5pt; font-family: Calibri, sans-serif;" class=""><span lang="EN-US" class=""><o:p class=""> </o:p></span></div><div style="margin: 0cm 0cm 0.0001pt; text-align: justify; font-size: 10.5pt; font-family: Calibri, sans-serif;" class=""><span lang="EN-US" class="">*********************************************<o:p class=""></o:p></span></div><div style="margin: 0cm 0cm 0.0001pt; text-align: justify; font-size: 10.5pt; font-family: Calibri, sans-serif;" class=""><span lang="EN-US" class="">// Go through implicit defs of CSMI and MI, if a def is not dead at MI,<o:p class=""></o:p></span></div><div style="margin: 0cm 0cm 0.0001pt; text-align: justify; font-size: 10.5pt; font-family: Calibri, sans-serif;" class=""><span lang="EN-US" class="">// we should make sure it is not dead at CSMI.<o:p class=""></o:p></span></div><div style="margin: 0cm 0cm 0.0001pt; text-align: justify; font-size: 10.5pt; font-family: Calibri, sans-serif;" class=""><span lang="EN-US" class="">if (MO.isImplicit() && !MO.isDead() && CSMI->getOperand(i).isDead())<o:p class=""></o:p></span></div><div style="margin: 0cm 0cm 0.0001pt; text-align: justify; font-size: 10.5pt; font-family: Calibri, sans-serif;" class=""><span lang="EN-US" class=""> ImplicitDefsToUpdate.push_back(i);<o:p class=""></o:p></span></div><div style="margin: 0cm 0cm 0.0001pt; text-align: justify; font-size: 10.5pt; font-family: Calibri, sans-serif;" class=""><span lang="EN-US" class=""><o:p class=""> </o:p></span></div><div style="margin: 0cm 0cm 0.0001pt; text-align: justify; font-size: 10.5pt; font-family: Calibri, sans-serif;" class=""><span lang="EN-US" class="">// Keep track of implicit defs of CSMI and MI, to clear possibly<o:p class=""></o:p></span></div><div style="margin: 0cm 0cm 0.0001pt; text-align: justify; font-size: 10.5pt; font-family: Calibri, sans-serif;" class=""><span lang="EN-US" class="">// made-redundant kill flags.<o:p class=""></o:p></span></div><div style="margin: 0cm 0cm 0.0001pt; text-align: justify; font-size: 10.5pt; font-family: Calibri, sans-serif;" class=""><span lang="EN-US" class="">if (MO.isImplicit() && !MO.isDead() && OldReg == NewReg)<o:p class=""></o:p></span></div><div style="margin: 0cm 0cm 0.0001pt; text-align: justify; font-size: 10.5pt; font-family: Calibri, sans-serif;" class=""><span lang="EN-US" class=""> ImplicitDefs.push_back(OldReg);<o:p class=""></o:p></span></div><div style="margin: 0cm 0cm 0.0001pt; text-align: justify; font-size: 10.5pt; font-family: Calibri, sans-serif;" class=""><span lang="EN-US" class=""><o:p class=""> </o:p></span></div><div style="margin: 0cm 0cm 0.0001pt; text-align: justify; font-size: 10.5pt; font-family: Calibri, sans-serif;" class=""><span lang="EN-US" class="">if (OldReg == NewReg) {<o:p class=""></o:p></span></div><div style="margin: 0cm 0cm 0.0001pt; text-align: justify; font-size: 10.5pt; font-family: Calibri, sans-serif;" class=""><span lang="EN-US" class=""> --NumDefs;<o:p class=""></o:p></span></div><div style="margin: 0cm 0cm 0.0001pt; text-align: justify; font-size: 10.5pt; font-family: Calibri, sans-serif;" class=""><span lang="EN-US" class=""> continue;<o:p class=""></o:p></span></div><div style="margin: 0cm 0cm 0.0001pt; text-align: justify; font-size: 10.5pt; font-family: Calibri, sans-serif;" class=""><span lang="EN-US" class="">}<o:p class=""></o:p></span></div><div style="margin: 0cm 0cm 0.0001pt; text-align: justify; font-size: 10.5pt; font-family: Calibri, sans-serif;" class=""><span lang="EN-US" class="">**********************************************<o:p class=""></o:p></span></div><div style="margin: 0cm 0cm 0.0001pt; text-align: justify; font-size: 10.5pt; font-family: Calibri, sans-serif;" class=""><span lang="EN-US" class=""><o:p class=""> </o:p></span></div><div style="margin: 0cm 0cm 0.0001pt; text-align: justify; font-size: 10.5pt; font-family: Calibri, sans-serif;" class=""><span lang="EN-US" class="">From Above source code, it seems that CSE does not handle instruction which<o:p class=""></o:p></span></div><div style="margin: 0cm 0cm 0.0001pt; text-align: justify; font-size: 10.5pt; font-family: Calibri, sans-serif;" class=""><span lang="EN-US" class="">have one operand that is ‘implicit+isDead+isDef’.<o:p class=""></o:p></span></div><div style="margin: 0cm 0cm 0.0001pt; text-align: justify; font-size: 10.5pt; font-family: Calibri, sans-serif;" class=""><span lang="EN-US" class=""><o:p class=""> </o:p></span></div><div style="margin: 0cm 0cm 0.0001pt; text-align: justify; font-size: 10.5pt; font-family: Calibri, sans-serif;" class=""><span lang="EN-US" class="">Base on my understanding, implicit dead register is mean clobbered, so it is not safe to<o:p class=""></o:p></span></div><div style="margin: 0cm 0cm 0.0001pt; text-align: justify; font-size: 10.5pt; font-family: Calibri, sans-serif;" class=""><span lang="EN-US" class="">do CSE. Is this right?<o:p class=""></o:p></span></div><div style="margin: 0cm 0cm 0.0001pt; text-align: justify; font-size: 10.5pt; font-family: Calibri, sans-serif;" class=""><span lang="EN-US" class=""><o:p class=""> </o:p></span></div><div style="margin: 0cm 0cm 0.0001pt; text-align: justify; font-size: 10.5pt; font-family: Calibri, sans-serif;" class=""><span lang="EN-US" class="">Best wishes<o:p class=""></o:p></span></div><div style="margin: 0cm 0cm 0.0001pt; text-align: justify; font-size: 10.5pt; font-family: Calibri, sans-serif;" class=""><span lang="EN-US" class="">Michael<o:p class=""></o:p></span></div><div style="margin: 0cm 0cm 0.0001pt; text-align: justify; font-size: 10.5pt; font-family: Calibri, sans-serif;" class=""><span lang="EN-US" class=""><o:p class=""> </o:p></span></div></div><span style="caret-color: rgb(0, 0, 0); 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; text-decoration: none; float: none; display: inline !important;" class="">_______________________________________________</span><br style="caret-color: rgb(0, 0, 0); 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; text-decoration: none;" class=""><span style="caret-color: rgb(0, 0, 0); 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; text-decoration: none; float: none; display: inline !important;" class="">LLVM Developers mailing list</span><br style="caret-color: rgb(0, 0, 0); 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; text-decoration: none;" 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="caret-color: rgb(0, 0, 0); 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; text-decoration: none;" 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></div></div>_______________________________________________<br class="">LLVM Developers mailing list<br class=""><a href="mailto:llvm-dev@lists.llvm.org" class="">llvm-dev@lists.llvm.org</a><br class="">http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev<br class=""></div></blockquote></div><br class=""></body></html>