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c13c09106e
routines and fix all of the bugs they expose. I hit a test case that crashed even without these asserts due to passing a non-exiting latch to the ExitingBlock parameter of the trip count computation machinery. However, when I add the nice asserts, it turns out we have plenty of coverage of these bugs, they just didn't manifest in crashers. The core problem seems to stem from an assumption that the latch *is* the exiting block. While this is often true, and somewhat the "normal" way to think about loops, it isn't necessarily true. The correct way to call the trip count routines in a *generic* fashion (that is, without a particular exit in mind) is to just use the loop's single exiting block if it has one. The trip count can't be computed generically unless it does. This works great for the loop vectorizer. The loop unroller actually *wants* to select the latch when it has to chose between multiple exits because for unrolling it is the latch trips that matter. But if this is the desire, it needs to explicitly guard for non-exiting latches and check for the generic trip count in that case. I've added the asserts, and added convenience APIs for querying the trip count generically that check for a single exit block. I've kept the APIs consistent between computing trip count and trip multiples. Thansk to Mark for the help debugging and tracking down the *right* fix here! git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219550 91177308-0d34-0410-b5e6-96231b3b80d8 |
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