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...For example: %y = xor %x, %x and: %y = xor %x, %z If %x and %z are undef you can’t differentiate these anymore: %y = xor undef, undef — Mehdi -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20161019/81b90053/attachment-0001.html>

Hi Krzysztof, freeze(poison) is different from undef today, in the sense that it is an instruction that produces some random, but fixed bit pattern. E.g. today in %x = undef %y = xor %x, %x we can fold %y to undef since each use of %x can independently see some arbitrary (up to the compiler / environment) bit pattern. But in the new proposal, in: %x = freeze(poison) %y = xor