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

Tue Aug 4 21:55:30 PDT 2020

aqjune added a comment.

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.
I think it is safer to 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.

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https://reviews.llvm.org/D85184