[llvm] [VPlan] Make canonical IV part of the region (PR #156262)

[Florian Hahn via llvm-commits]

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@@ -9520,55 +9516,55 @@ static SmallVector<Instruction *> preparePlanForEpilogueVectorLoop(
   VPBasicBlock *Header = VectorLoop->getEntryBasicBlock();
   Header->setName("vec.epilog.vector.body");
 
-  DenseMap<Value *, Value *> ToFrozen;
   SmallVector<Instruction *> InstsToMove;
+  DenseMap<Value *, Value *> ToFrozen;
   // Ensure that the start values for all header phi recipes are updated before
   // vectorizing the epilogue loop.
-  for (VPRecipeBase &R : Header->phis()) {
-    if (auto *IV = dyn_cast<VPCanonicalIVPHIRecipe>(&R)) {
-      // When vectorizing the epilogue loop, the canonical induction start
-      // value needs to be changed from zero to the value after the main
-      // vector loop. Find the resume value created during execution of the main
-      // VPlan. It must be the first phi in the loop preheader.
-      // FIXME: Improve modeling for canonical IV start values in the epilogue
-      // loop.
-      using namespace llvm::PatternMatch;
-      PHINode *EPResumeVal = &*L->getLoopPreheader()->phis().begin();
-      for (Value *Inc : EPResumeVal->incoming_values()) {
-        if (match(Inc, m_SpecificInt(0)))
-          continue;
-        assert(!EPI.VectorTripCount &&
-               "Must only have a single non-zero incoming value");
-        EPI.VectorTripCount = Inc;
-      }
-      // If we didn't find a non-zero vector trip count, all incoming values
-      // must be zero, which also means the vector trip count is zero. Pick the
-      // first zero as vector trip count.
-      // TODO: We should not choose VF * UF so the main vector loop is known to
-      // be dead.
-      if (!EPI.VectorTripCount) {
-        assert(
-            EPResumeVal->getNumIncomingValues() > 0 &&
-            all_of(EPResumeVal->incoming_values(),
-                   [](Value *Inc) { return match(Inc, m_SpecificInt(0)); }) &&
-            "all incoming values must be 0");
-        EPI.VectorTripCount = EPResumeVal->getOperand(0);
-      }
-      VPValue *VPV = Plan.getOrAddLiveIn(EPResumeVal);
-      assert(all_of(IV->users(),
-                    [](const VPUser *U) {
-                      return isa<VPScalarIVStepsRecipe>(U) ||
-                             isa<VPDerivedIVRecipe>(U) ||
-                             cast<VPRecipeBase>(U)->isScalarCast() ||
-                             cast<VPInstruction>(U)->getOpcode() ==
-                                 Instruction::Add;
-                    }) &&
-             "the canonical IV should only be used by its increment or "
-             "ScalarIVSteps when resetting the start value");
-      IV->setOperand(0, VPV);
+  auto *IV = Plan.getCanonicalIV();
+  // When vectorizing the epilogue loop, the canonical induction start value
+  // needs to be changed from zero to the value after the main vector loop. Find
+  // the resume value created during execution of the main VPlan.
+  // FIXME: Improve modeling for canonical IV start values in the epilogue loop.
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fhahn wrote:

Should be adjusted as part of https://github.com/llvm/llvm-project/pull/161589, thanks

https://github.com/llvm/llvm-project/pull/156262