[llvm] [VPlan] Create epilogue minimum iteration check in VPlan. (PR #157545)

[Florian Hahn via llvm-commits]

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@@ -7405,124 +7391,27 @@ BasicBlock *EpilogueVectorizerMainLoop::emitIterationCountCheck(
 // EpilogueVectorizerEpilogueLoop
 //===--------------------------------------------------------------------===//
 
-/// This function is partially responsible for generating the control flow
-/// depicted in https://llvm.org/docs/Vectorizers.html#epilogue-vectorization.
+/// This function creates a new scalar preheader, using the previous one as
+/// entry block to the epilogue VPlan. The minimum iteration check is already
+/// created in VPlan.
 BasicBlock *EpilogueVectorizerEpilogueLoop::createVectorizedLoopSkeleton() {
+  BasicBlock *OriginalScalarPH = OrigLoop->getLoopPreheader();
   BasicBlock *ScalarPH = createScalarPreheader("vec.epilog.");
-  BasicBlock *VectorPH = ScalarPH->getSinglePredecessor();
-  // Now, compare the remaining count and if there aren't enough iterations to
-  // execute the vectorized epilogue skip to the scalar part.
-  VectorPH->setName("vec.epilog.ph");
-  BasicBlock *VecEpilogueIterationCountCheck =
-      SplitBlock(VectorPH, VectorPH->begin(), DT, LI, nullptr,
-                 "vec.epilog.iter.check", true);
-  VectorPHVPBB = replaceVPBBWithIRVPBB(VectorPHVPBB, VectorPH);
-
-  emitMinimumVectorEpilogueIterCountCheck(VectorPH, ScalarPH,
-                                          VecEpilogueIterationCountCheck);
-  AdditionalBypassBlock = VecEpilogueIterationCountCheck;
-
-  // Adjust the control flow taking the state info from the main loop
-  // vectorization into account.
-  assert(EPI.MainLoopIterationCountCheck && EPI.EpilogueIterationCountCheck &&
-         "expected this to be saved from the previous pass.");
-  EPI.MainLoopIterationCountCheck->getTerminator()->replaceUsesOfWith(
-      VecEpilogueIterationCountCheck, VectorPH);
-
-  EPI.EpilogueIterationCountCheck->getTerminator()->replaceUsesOfWith(
-      VecEpilogueIterationCountCheck, ScalarPH);
-
-  // Adjust the terminators of runtime check blocks and phis using them.
-  BasicBlock *SCEVCheckBlock = RTChecks.getSCEVChecks().second;
-  BasicBlock *MemCheckBlock = RTChecks.getMemRuntimeChecks().second;
-  if (SCEVCheckBlock)
-    SCEVCheckBlock->getTerminator()->replaceUsesOfWith(
-        VecEpilogueIterationCountCheck, ScalarPH);
-  if (MemCheckBlock)
-    MemCheckBlock->getTerminator()->replaceUsesOfWith(
-        VecEpilogueIterationCountCheck, ScalarPH);
-
-  DT->changeImmediateDominator(ScalarPH, EPI.EpilogueIterationCountCheck);
-
-  // The vec.epilog.iter.check block may contain Phi nodes from inductions or
-  // reductions which merge control-flow from the latch block and the middle
-  // block. Update the incoming values here and move the Phi into the preheader.
-  SmallVector<PHINode *, 4> PhisInBlock(
-      llvm::make_pointer_range(VecEpilogueIterationCountCheck->phis()));
-
-  for (PHINode *Phi : PhisInBlock) {
-    Phi->moveBefore(VectorPH->getFirstNonPHIIt());
-    Phi->replaceIncomingBlockWith(
-        VecEpilogueIterationCountCheck->getSinglePredecessor(),
-        VecEpilogueIterationCountCheck);
-
-    // If the phi doesn't have an incoming value from the
-    // EpilogueIterationCountCheck, we are done. Otherwise remove the incoming
-    // value and also those from other check blocks. This is needed for
-    // reduction phis only.
-    if (none_of(Phi->blocks(), [&](BasicBlock *IncB) {
-          return EPI.EpilogueIterationCountCheck == IncB;
-        }))
+  OriginalScalarPH->setName("vec.epilog.iter.check");
+  VPIRBasicBlock *NewEntry = Plan.createVPIRBasicBlock(OriginalScalarPH);
+  VPBasicBlock *OldEntry = Plan.getEntry();
+  for (auto &R : make_early_inc_range(
+           make_range(OldEntry->getFirstNonPhi(), OldEntry->end()))) {
+    if (isa<VPIRInstruction>(&R))
----------------
fhahn wrote:

Added a comment and also updated to iterate over all recipes.

https://github.com/llvm/llvm-project/pull/157545