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...there is no point in doing so. So is there any other way of having “undef” appear in the IR ? Peter Lawrence. > On Jun 16, 2017, at 7:45 PM, Sanjoy Das <sanjoy at playingwithpointers.com> wrote: > > Hi Peter, > > Why we need an undef value is covered here: > http://sunfishcode.github.io/blog/2014/07/14/undef-introduction.html > (in short, to do SSA construction well). > > For a while we did not have a literal representation for poison. > However, in practice having both undef and poison was problematic (see > the paper), so we decided to ditch undef and...

All, These discussions seem to be based on the premise that there is a need for the compiler to exploit undefined behavior for performance optimization reasons. So far the only beneficial optimization I am aware of that relies on some form of “undefined” is Dan Gohman’s original project for LP64 targets of promoting i32 induction variables to i64 and hoisting sign-extension out of the

Hello all, I am wondering the use case of undef. Is there any C code that I could get undef if it is compiled by clang. Thanks -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20161204/7ab81194/attachment.html>