[llvm] [VPlan] Dispatch to multiple exit blocks via middle blocks. (PR #112138)

[David Sherwood via llvm-commits]

================
@@ -1696,3 +1702,79 @@ void VPlanTransforms::createInterleaveGroups(
       }
   }
 }
+
+void VPlanTransforms::convertToMultiCond(VPlan &Plan, ScalarEvolution &SE,
+                                         Loop *OrigLoop,
+                                         VPRecipeBuilder &RecipeBuilder) {
+  auto *LatchVPBB =
+      cast<VPBasicBlock>(Plan.getVectorLoopRegion()->getExiting());
+  VPBuilder Builder(LatchVPBB->getTerminator());
+  auto *MiddleVPBB =
+      cast<VPBasicBlock>(Plan.getVectorLoopRegion()->getSingleSuccessor());
+
+  VPRegionBlock *LoopRegion = Plan.getVectorLoopRegion();
+
+  const SCEV *BackedgeTakenCount =
+      SE.getExitCount(OrigLoop, OrigLoop->getLoopLatch());
+  const SCEV *TripCount = SE.getTripCountFromExitCount(
+      BackedgeTakenCount, Plan.getCanonicalIV()->getScalarType(), OrigLoop);
+  VPValue *NewTC = vputils::getOrCreateVPValueForSCEVExpr(Plan, TripCount, SE);
+  Plan.getTripCount()->replaceAllUsesWith(NewTC);
+  Plan.resetTripCount(NewTC);
----------------
david-arm wrote:

I don't think you need this code - the existing trip count already uses the predicated symbolic max backedge taken count.

https://github.com/llvm/llvm-project/pull/112138