[PATCH] D95238: [LangRef] Update memory access ops to raise UB if ptrs are not well defined

[Juneyoung Lee via Phabricator via llvm-commits]

aqjune added inline comments.


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Comment at: llvm/docs/LangRef.rst:12697
+If ``<len>`` is 0, the pointers may be NULL, dangling, ``undef``, or ``poison``
 pointers. However, they must still be appropriately aligned.
+If ``<len>`` is not a well-defined value, the behavior is undefined.
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jdoerfert wrote:
> Partially related: I never understood the alignment thing. `undef` and `poison` are not aligned. Violating `align` should result in a `poison` value, which we had in the first place. We should check why this is her.
Initially, the constraint of alignment was introduced by D57600 after the discussion at https://bugs.llvm.org/show_bug.cgi?id=38583 .

Then, the semantics of passing undef/poison pointers to memcpy/memset was clarified by D86643.
At that point, violation of align attribute was still undefined behavior.

Then, D90529 updated the semantics of align to return poison instead.
Now, align attribute has no effect if the size is zero (unless noundef is there too).

I fixed the sentences here to be modular w.r.t. the semantics of attributes.


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  https://reviews.llvm.org/D95238/new/

https://reviews.llvm.org/D95238