[PATCH] D104648: [Mem2Reg] Use poison instead of undef for read of uninitialized memory

[Nuno Lopes via Phabricator via llvm-commits]

nlopes added a comment.

In D104648#2836258 <https://reviews.llvm.org/D104648#2836258>, @aqjune wrote:

> Or, can we temporarily mark an alloca with `!has_bitfield` if it had bitfields in C & make mem2reg use poison only when uninitialized memory is read, for a while?

Well, that doesn't help much. It's just a band-aid..
I would rather initialize all alloca'd bitfields with zero instead. Zero folds trivially with the bit-masking operations from bit-fields, so it's unlikely to disrupt anything.


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