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...I don't follow this last sentence. if the definition of NUW is that zext-ing the result is equivalent to zext-ing the inputs and doing the operation at a higher bitwidth (my understanding), then %m and %n cannot hold those values, that would violate the NUW flag. Either my understanding of th edefinition holds, or the transformation you are proposing isn't valid IMO. -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20150127/bd36ea4b/attachment.html>

On Tue, Jan 27, 2015 at 8:32 PM, Sanjoy Das <sanjoy at playingwithpointers.com> wrote: > > > > Correct me if I am wrong but we are talking about transforming: > > %maybe_poison = add nuw i32 %a, %b > > %x = zext i32 %maybe_poison to i64 > > %y = lshr i64 %x 32 > > > > To: > > %za = zext i32 %a to i64 > > %zb = zext i32 %b