[llvm] 2eab83f - [VPlan] Remove CanonicalIV when dissolving loop regions (NFC). (#142372)

[via llvm-commits]

Author: Florian Hahn
Date: 2025-06-03T10:05:28+01:00
New Revision: 2eab83f6187c82c56535a77a44f1fc1cac860686

URL: https://github.com/llvm/llvm-project/commit/2eab83f6187c82c56535a77a44f1fc1cac860686
DIFF: https://github.com/llvm/llvm-project/commit/2eab83f6187c82c56535a77a44f1fc1cac860686.diff

LOG: [VPlan] Remove CanonicalIV when dissolving loop regions (NFC). (#142372)

Directly replace the canonical IV when we dissolve the containing
region. That ensures that it won't get removed before the region gets
removed, which would result in an invalid region.

This removes the current ordering constraint between
convertToConcreteRecipes and dissolving regions.

PR: https://github.com/llvm/llvm-project/pull/142372

Added: 
    

Modified: 
    llvm/lib/Transforms/Vectorize/VPlan.cpp
    llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp

Removed: 
    


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diff  --git a/llvm/lib/Transforms/Vectorize/VPlan.cpp b/llvm/lib/Transforms/Vectorize/VPlan.cpp
index 165b57c87beb1..280ea47c5d7cc 100644
--- a/llvm/lib/Transforms/Vectorize/VPlan.cpp
+++ b/llvm/lib/Transforms/Vectorize/VPlan.cpp
@@ -883,6 +883,16 @@ void VPRegionBlock::print(raw_ostream &O, const Twine &Indent,
 
 void VPRegionBlock::dissolveToCFGLoop() {
   auto *Header = cast<VPBasicBlock>(getEntry());
+  if (auto *CanIV = dyn_cast<VPCanonicalIVPHIRecipe>(&Header->front())) {
+    assert(this == getPlan()->getVectorLoopRegion() &&
+           "Canonical IV must be in the entry of the top-level loop region");
+    auto *ScalarR = VPBuilder(CanIV).createScalarPhi(
+        {CanIV->getStartValue(), CanIV->getBackedgeValue()},
+        CanIV->getDebugLoc(), "index");
+    CanIV->replaceAllUsesWith(ScalarR);
+    CanIV->eraseFromParent();
+  }
+
   VPBlockBase *Preheader = getSinglePredecessor();
   auto *ExitingLatch = cast<VPBasicBlock>(getExiting());
   VPBlockBase *Middle = getSingleSuccessor();

diff  --git a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
index 348100124ba3c..ea617f042566b 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
+++ b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
@@ -2599,14 +2599,10 @@ void VPlanTransforms::convertToConcreteRecipes(VPlan &Plan,
   for (VPBasicBlock *VPBB : VPBlockUtils::blocksOnly<VPBasicBlock>(
            vp_depth_first_deep(Plan.getEntry()))) {
     for (VPRecipeBase &R : make_early_inc_range(*VPBB)) {
-      if (isa<VPCanonicalIVPHIRecipe, VPEVLBasedIVPHIRecipe>(&R)) {
-        auto *PhiR = cast<VPHeaderPHIRecipe>(&R);
-        StringRef Name =
-            isa<VPCanonicalIVPHIRecipe>(PhiR) ? "index" : "evl.based.iv";
-        VPBuilder Builder(PhiR);
-        auto *ScalarR = Builder.createScalarPhi(
+      if (auto *PhiR = dyn_cast<VPEVLBasedIVPHIRecipe>(&R)) {
+        auto *ScalarR = VPBuilder(PhiR).createScalarPhi(
             {PhiR->getStartValue(), PhiR->getBackedgeValue()},
-            PhiR->getDebugLoc(), Name);
+            PhiR->getDebugLoc(), "evl.based.iv");
         PhiR->replaceAllUsesWith(ScalarR);
         ToRemove.push_back(PhiR);
         continue;