<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 Aug 18, 2021, at 21:21, Rohit Aggarwal 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=""><br class=""><div class="gmail_quote"><div dir="ltr" class="gmail_attr">Hi All,<br class=""></div><div dir="ltr" class=""><div class=""><br class=""></div><div class="">I am running the instcombine pass on the given lR and executing the binary.</div><div class=""><br class=""></div><div class=""><i class="">./build_release13x/bin/opt -enable-new-pm=false -instcombine sample.ll -S -o sample_instcombined_llvm.ll && ./build_release13x/bin/clang sample_instcombined_llvm.ll && ./a.out</i><br class=""></div><div class=""><i class=""><br class=""></i></div><div class="">But before passing to instcombine, the output is <b class="">CE6DB4AC</b> and after passing to instcombine value changes to <b class="">3B83FBC</b>.</div><div class=""><br class=""></div><div class="">I tried to debug the issue and found that due to the occurence of poison value, some instructions(or, store,..) are getting deleted/erased. </div><div class=""><b class=""><br class=""></b></div><div class="">I also observed that there are active changes happening related to poison values in the community. Is this behaviour expected one? Or Could it be a side effect of those changes</div></div></div></div></div></blockquote></div><br class=""><div class="">There are 2 potential causes for the difference: 1) your input has undefined behavior and/or the result depends on a poison value or 2) a bug in instcombine. </div><div class=""><br class=""></div><div class="">Without narrowing things down to the problematic pattern, it is very hard to say which one it is. I’d suggest you try to isolate the change in behavior to the problematic instcombine pattern and minimize the input IR to trigger the problematic pattern. </div><div class=""><br class=""></div><div class="">Cheers,</div><div class="">Florian</div></body></html>