[PATCH] D100717: [InstCombine] Transform memcpy to ptr load/stores if TBAA says so

[Juneyoung Lee via Phabricator via llvm-commits]

aqjune added a comment.

In D100717#2697125 <https://reviews.llvm.org/D100717#2697125>, @fhahn wrote:

> I don't see how this use of TBAA metadata is within the specification of the metadata.
>
> IIUC the type descriptors only encode the layout and relationship between types, but not whether a scalar type is a pointer, integer, floating point or other type. It just happens to be that Clang uses names that are related to the source types. But IIUC those names are arbitrary and Clang could just as well use `A`, `B`, `C`,... or any other naming scheme.
>
> Please let me know if I am missing something that provides the guarantees the patch uses.

For metadata nodes whose descriptions are simply C/C++'s type name they shouldn't carry info, but for those with special descriptions would it be reasonable if they are given special meaning?
I thought TBAA used the description because `MDNode::isTBAAVtableAccess` checks whether description is `"vtable pointer"`.


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