<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="">Hi,<br class=""><div><br class=""><blockquote type="cite" class=""><div class="">On Mar 6, 2019, at 9:58 AM, Son Tuan VU 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 dir="ltr" class=""><div dir="ltr" class=""><div dir="ltr" class=""><div dir="ltr" class=""><div class="">Hello,</div><div class=""><br class=""></div><div class="">I found this thread back in 2014 [1] . Does anyone know if there has been any attempt to answer this request?</div><div class=""><br class=""></div><div class="">To clarify, I am looking for an analysis that computes the textbook definition of variable liveness: "given a SSA value V and a point P, is there a possible path from P to any use of V?" which is equivalent to "is V live at point P?"</div><div class=""><br class=""></div><div class="">I can write something myself (and will if need be), but just want to avoid reinventing the wheels in case improvements have been made since 2014. If not, what's the best way to contribute this analysis to LLVM? I mean, for example, is "Computing Liveness Sets for SSA" by Boissinot [2] efficient enough to be implemented in LLVM?</div></div></div></div></div></div></blockquote><div><br class=""></div><div>This one should be efficient enough.</div><div>That said, what are you trying to achieve?</div><div><br class=""></div><div>The reason we don’t have such algorithm in LLVM IR is because we don’t need it. Usually def-uses chains and dominance property are enough for what the optimizers want to do.</div><br class=""><blockquote type="cite" class=""><div class=""><div dir="ltr" class=""><div dir="ltr" class=""><div dir="ltr" class=""><div dir="ltr" class=""><div class=""> Or should I find a better algorithm to solve this?<br class=""></div><div class=""><br class=""></div><div class="">[1] <a href="http://lists.llvm.org/pipermail/llvm-dev/2014-July/074793.html" class="">http://lists.llvm.org/pipermail/llvm-dev/2014-July/074793.html</a></div><div class="">[2] <a href="http://hal.inria.fr/docs/00/58/53/03/PDF/RR-7503.pdf" class="">http://hal.inria.fr/docs/00/58/53/03/PDF/RR-7503.pdf</a><br class=""></div><div class=""><br class=""></div><div class="">Thanks for your help,</div><div class=""><br class=""></div><div class="">Cheers</div><div class=""><br class=""></div><div class=""></div><div class=""><div class=""><div dir="ltr" class="gmail_signature"><div dir="ltr" class="">Son Tuan Vu</div></div></div></div></div></div></div></div>
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