[PATCH] D103261: [AMDGPU] Increase alignment of LDS globals if necessary before LDS lowering.

[Jon Chesterfield via Phabricator via llvm-commits]

JonChesterfield added a comment.

I'm not very convinced by this given the recent enthusiasm for decreasing LDS usage. Types are naturally aligned by default, so I think the only time they are aligned by less than that is when the programmer asked for it (or when the vectorizer is involved, but that's disabled on amdgpu afaik).

If someone has a char data[16] __align__(4) in LDS, i'm not at all sure it's obvious that they want the alignment increased to 16, despite that using more LDS than they asked for.

We could do something more conservative, where we put variables in order based on their sizes and alignments, and then go through the resulting struct and tag variables with the additional alignment they happen to have as a result of position in the struct. That would be pure performance win, zero storage overhead cost. It leaves the choice to burn memory in favour of faster instructions in the hands of the developer writing the code.


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https://reviews.llvm.org/D103261