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db67d035c2
This shows up as a side issue to the main problem for the AVX target example from PR37428: https://bugs.llvm.org/show_bug.cgi?id=37428 - https://godbolt.org/z/7tpRa3 But as we can see in the pile of existing test diffs, it's actually a widespread problem that affects any AVX or later target. Apart from a couple of oddballs, I think these are all improvements for the reasons stated in the code comment: we do not want to enable YMM unnecessarily (avoid vzeroupper and frequency throttling) and some cores split 256-bit stores anyway. We could say that MergeConsecutiveStores() is going overboard on some of these examples, but that won't solve the problem completely. But that is a reason I'm proposing this as a lowering rather than a combine: we will infinite loop fighting the merge code if we try this earlier. Differential Revision: https://reviews.llvm.org/D62498 llvm-svn: 362524