[PATCH] D95122: [Libcalls, Attrs] Annotate libcalls with noundef

[Juneyoung Lee via Phabricator via llvm-commits]

aqjune added a comment.

In D95122#2512578 <https://reviews.llvm.org/D95122#2512578>, @xbolva00 wrote:

> but we are talking about specific libcalls, so eg. strlen(p), where p is null, is UB.

The problem is that in theory p can be partially undef which is still dereferenceable. Imagine a pointer that points into somewhere within bounds of alloca [16 x i8] but the lowest 4 bits of the offset is undefined.
If strlen's first argument has noundef, this will also be UB, which is more undefined than before.


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