[PATCH] D71499: Add builtins for aligning and checking alignment of pointers and integers

[Alexander Richardson via Phabricator via cfe-commits]

arichardson added a comment.

In D71499#1801104 <https://reviews.llvm.org/D71499#1801104>, @lebedev.ri wrote:

> Looks ok to me now in principle.
>  I have one more question about pointer variants though (see inline)


I am not sure the GEP can be inbounds since I have seen some cases where aligning pointers is used to get a pointer to a different object.
I most cases it should be in-bounds (even when used to implement `malloc()`), but I have seen some cases where aligning pointers is used to get a pointer to a different object.
For example, some versions WebKit align pointers down by 64k to get a pointer to a structure that holds metadata for all objects allocated inside that region.

I am not sure what happens for those cases if we add inbounds (miscompilation?), so I haven't added it here.
I guess we could add it if alignment is a constant and is less than the object size, but there might already be a pass to infer if a GEP is inbounds?


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https://reviews.llvm.org/D71499