[llvm] [VPlan] Model branch cond to enter scalar epilogue in VPlan. (PR #92651)

[Florian Hahn via llvm-commits]

================
@@ -795,6 +833,35 @@ VPlanPtr VPlan::createInitialVPlan(const SCEV *TripCount, ScalarEvolution &SE,
   VPBlockUtils::insertBlockAfter(TopRegion, VecPreheader);
   VPBasicBlock *MiddleVPBB = new VPBasicBlock("middle.block");
   VPBlockUtils::insertBlockAfter(MiddleVPBB, TopRegion);
+
+  BasicBlock *EB = TheLoop->getUniqueExitBlock();
+  if (RequiresScalarEpilogueCheck) {
+    auto *EBWrapper = new VPIRBasicBlock(EB);
+    VPBlockUtils::insertBlockAfter(EBWrapper, MiddleVPBB);
+
+    auto *ScalarLatchTerm = TheLoop->getLoopLatch()->getTerminator();
+    // Here we use the same DebugLoc as the scalar loop latch terminator instead
+    // of the corresponding compare because they may have ended up with
+    // different line numbers and we want to avoid awkward line stepping while
+    // debugging. Eg. if the compare has got a line number inside the loop.
+    VPValue *Cmp =
+        TailFolded
+            ? Plan->getOrAddLiveIn(ConstantInt::getTrue(
+                  IntegerType::getInt1Ty(TripCount->getType()->getContext())))
----------------
fhahn wrote:

I've left things as is for now to reduce the number of changes. Would be good to adjust separately once we model the branch in the middle block.

https://github.com/llvm/llvm-project/pull/92651