<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">Hi Chad<div class=""><div class=""><br class=""></div><div class=""><a href="http://reviews.llvm.org/D6048" class="">http://reviews.llvm.org/D6048</a> (everyone CCed here was CCed on it) added register liveness checking to the CondOpt pass. It does this with</div><div class=""><br class=""></div><blockquote style="margin: 0 0 0 40px; border: none; padding: 0px;" class=""><div class="">if (I->getOperand(0).isDead())</div></blockquote><div class=""><br class=""></div><div class="">However, this requires that some kind of liveness has been run beforehand, so the pass had to require live intervals. Looking at the pass manager dump, we then invalidated live intervals shortly after CondOpt because other passes don’t preserve it.</div><div class=""><br class=""></div><div class="">Attached is a patch which removes the dependency on LiveIntervals by checking if the def has any uses. If it has no uses then it was going to be marked dead anyway, so this is equivalent to your original code. I’ve verified that this passes ‘make check’ and specifically stepped through the examples in combine-comparisons-by-cse.ll in lldb to ensure the behavior was the same.</div><div class=""><br class=""></div><div class="">When building a bitcode containing all of llc with/without this change, it results in one less run of LiveIntervals per MF and saves 4s out of 80s total compile time.</div><div class=""><br class=""></div><div class="">Thanks,</div><div class="">Pete</div><div class=""><br class=""></div><div class=""><br class=""></div><div class=""></div></div></body></html>