[llvm] [VPlan] Delay adding canonical IV increment and exit branches. (PR #82270)

[via llvm-commits]

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@@ -1235,16 +1235,10 @@ void VPlanTransforms::optimize(VPlan &Plan, ScalarEvolution &SE) {
 static VPActiveLaneMaskPHIRecipe *addVPLaneMaskPhiAndUpdateExitBranch(
     VPlan &Plan, bool DataAndControlFlowWithoutRuntimeCheck) {
   VPRegionBlock *TopRegion = Plan.getVectorLoopRegion();
-  VPBasicBlock *EB = TopRegion->getExitingBasicBlock();
   auto *CanonicalIVPHI = Plan.getCanonicalIV();
   VPValue *StartV = CanonicalIVPHI->getStartValue();
 
-  auto *CanonicalIVIncrement =
-      cast<VPInstruction>(CanonicalIVPHI->getBackedgeValue());
-  // TODO: Check if dropping the flags is needed if
-  // !DataAndControlFlowWithoutRuntimeCheck.
-  CanonicalIVIncrement->dropPoisonGeneratingFlags();
-  DebugLoc DL = CanonicalIVIncrement->getDebugLoc();
+  DebugLoc DL = CanonicalIVPHI->getDebugLoc();
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ayalz wrote:

This is for an increment placed in the preheader, so ok to use the DL of the phi instead of that of the in-loop/backedged-value increment?

https://github.com/llvm/llvm-project/pull/82270