[clang] [llvm] [SROA] Vector promote some memsets (PR #133301)

[Nikita Popov via llvm-commits]

https://github.com/nikic requested changes to this pull request.

So if I understand correctly, you are marking memsets as unsplittable, lowering them to vector zero and smaller accesses to inserts/extracts.

I don't think your general approach here is going to work. We need to be careful about introducing vector operations out of thin air, because LLVM is not going to second guess them. If you convert a memset to <32768 x i8> ops here, LLVM is going to carry those all they down, even though this is almost certainly not performant. Additionally, you are breaking the ability for SROA to split the alloca and fully promote parts of it.



https://github.com/llvm/llvm-project/pull/133301