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

Tue Aug 4 23:32:02 PDT 2020

jdoerfert added a comment.

In D85184#2195356 <https://reviews.llvm.org/D85184#2195356>, @aqjune wrote:

> In D85184#2193446 <https://reviews.llvm.org/D85184#2193446>, @jdoerfert wrote:
>
>> Note: @aqjune,  and @okura  We should also seed `noundef` in the intrinsics and especially known library functions definitions. I mean, `malloc` is not returning a undef or poison value (I hope), and `free` is not accepting one.
>
> BuildLibCalls.cpp 's inferLibFuncAttributes seems to be the right place for this?
> I'll start with adding noundef to return values of library functions.

That would be great, and yest that is the right place for most of it IIRC.

> I think it is safer to

Safer than what?

> gradually add noundef to arguments of library functions, since it may cause end-to-end miscompilation (if there exists any incorrect transformation): IIRC there was a regression from strlen having nonnull attribute at its pointer argument, that happened from its interaction with llvm.assume.

I wouldn't be totally surprised if something explodes but it should not and it is good to know earlier if it does ;)

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D85184/new/

https://reviews.llvm.org/D85184