[llvm] [VPlan] Support early-exit loops in optimizeForVFAndUF. (PR #131539)

[Florian Hahn via llvm-commits]

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@@ -1019,9 +1046,12 @@ void VPlanTransforms::optimizeForVFAndUF(VPlan &Plan, ElementCount BestVF,
   //  1. BranchOnCount, or
   //  2. BranchOnCond where the input is Not(ActiveLaneMask).
   using namespace llvm::VPlanPatternMatch;
+  VPValue *Cond;
   if (!match(Term, m_BranchOnCount(m_VPValue(), m_VPValue())) &&
-      !match(Term,
-             m_BranchOnCond(m_Not(m_ActiveLaneMask(m_VPValue(), m_VPValue())))))
+      !match(Term, m_BranchOnCond(
+                       m_Not(m_ActiveLaneMask(m_VPValue(), m_VPValue())))) &&
+      (!match(Term, m_BranchOnCond(m_VPValue(Cond))) ||
+       isConditionKnown(Cond, Plan, BestVF, BestUF, *PSE.getSE())))
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fhahn wrote:

Ah yes, I should have broken up the checks for `BranchOnCount/BranchOnCond(activelanemask)` and `BranchOnCond` to make this clearer and also skip the checks for `BranchOnCount` if we have `BranchOnCond`. 

Should hopefully be clearer now.

https://github.com/llvm/llvm-project/pull/131539