[PATCH] D72396: [InstCombine] fold zext of masked bit set/clear

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri added a comment.

In D72396#1810034 <https://reviews.llvm.org/D72396#1810034>, @krasimir wrote:

> Internally, I can see that either (1) this causes the following code to miscompile, or (2) the code is UB:
>  https://github.com/grpc/grpc/blob/master/src/core/ext/transport/chttp2/transport/frame_settings.cc#L48
>  Note that in that code the two checks on lines 57 and 64 are related if that helps.


What is the maximal value of `count` there? Is it `count u< 32`? (Is that code UBSan-clean?)

> Working on providing a small reproducible test case.




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