[llvm] [LoopUnroll] Relax fixed non-latch exit probability threshold for runtime multi-exit loop unrolling (PR #224325)

[Marek Sedláček via llvm-commits]

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@@ -585,6 +590,14 @@ static bool canProfitablyRuntimeUnrollMultiExitLoop(
     // If BranchProbability could not be extracted (returns unknown), then
     // don't return and do the check for deopt block.
     if (!BranchProb.isUnknown()) {
+      // Special case for linear scan loop with trip count < ~100, which will
+      // not pass the P < 1/100 check bellow.
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mark-sed wrote:

> why don't we replace the old heuristic with this one? Or, in other words, what's the motivation for keeping the old one around?

That is a good point... I suppose it was just my conservative approach where I wanted to allow for the old threshold if MinBodies is 0, but now that you raised this, I suppose it should be rather removed. I will update that tomorrow, thanks.

https://github.com/llvm/llvm-project/pull/224325