[PATCH] D102615: [LoopDeletion] Break backedge if we can prove that the loop is exited on 1st iteration

[Max Kazantsev via Phabricator via llvm-commits]

mkazantsev added a comment.

In D102615#2764466 <https://reviews.llvm.org/D102615#2764466>, @reames wrote:

> I'm confused why this is worthwhile.  LoopUnrolling already knows how to symbolically execute a loop.  Shouldn't LoopUnroll fully unroll this loop by one - thus deleting the loop backedge in question?

Full unrolling is only possible when we know trip count, which is not the case here. There is a subtle difference between computing the trip count and proving that the trip count is zero. This patch is trying to make the latter in cases when it's not known.


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