[PATCH] D127392: [InstCombine] Combine consecutive loads which are being merged to form a wider load.

[Sanjay Patel via Phabricator via llvm-commits]

spatel added a reviewer: efriedma.
spatel added a comment.

I'd like to see some form of load combining in IR, but we need to be very careful about how that is implemented.

Note that LLVM had a dedicated pass for load combining, but it caused problems and was removed:
https://lists.llvm.org/pipermail/llvm-dev/2016-September/105291.html

So any proposal to do it again should be aware of and avoid those problems. Putting it in InstCombine is controversial because it could interfere with other analysis/passes. We recently added a cost-aware transform to AggressiveInstCombine, so that might be a better fit.

I didn't check all of the tests, but at least the simplest cases should already be handled in DAGCombiner. Can you show a larger, motivating example where that backend transform is too late to get to the ideal code?


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https://reviews.llvm.org/D127392