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

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Florian Hahn (fhahn)

<details>
<summary>Changes</summary>

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.

---
Full diff: https://github.com/llvm/llvm-project/pull/142372.diff


2 Files Affected:

- (modified) llvm/lib/Transforms/Vectorize/VPlan.cpp (+10) 
- (modified) llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp (+3-7) 


``````````diff
diff --git a/llvm/lib/Transforms/Vectorize/VPlan.cpp b/llvm/lib/Transforms/Vectorize/VPlan.cpp
index 165b57c87beb1..2580031c9186b 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 = Builder(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 5b42a9056b69e..5c6d7b0c5b529 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
+++ b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
@@ -2601,14 +2601,10 @@ 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 = Builder(PhiR).createScalarPhi(
             {PhiR->getStartValue(), PhiR->getBackedgeValue()},
-            PhiR->getDebugLoc(), Name);
+            PhiR->getDebugLoc(), "evl.based.iv");
         PhiR->replaceAllUsesWith(ScalarR);
         ToRemove.push_back(PhiR);
         continue;

``````````

</details>


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