[PATCH] D85184: [Attributor][WIP] Deduce noundef attribute

[Johannes Doerfert via Phabricator via llvm-commits]

jdoerfert added a comment.

In D85184#2197413 <https://reviews.llvm.org/D85184#2197413>, @aqjune wrote:

> I made D85345 <https://reviews.llvm.org/D85345>.

I saw, cool!

> Rather than adding noundef to all library functions' return values, I chose standard I/O functions and added noundef to its return values / arguments instead.
> The reason is that some functions did not seem to be clear whether its return value is noundef.
> `memcmp` is one example. `(load p) - (load q)` can be folded into `memcmp(p, q, bytesz)`, but the former expression can be poison or undef whereas the latter one raises UB in that case.

I don't think all of them should have `noundef` everywhere but some. The return of `malloc` and the argument of `free` were my examples. I/O as a start is good too.

> (than adding noundef to all library functions' args :)

I never tried to say "all" ;)

@okura there is one comment wrt. the MBEC context that needs to be addressed, I think the rest is fine.


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