[llvm] [VPlan] Fix assert in finding WideCanIV (NFC) (PR #193269)

[Ramkumar Ramachandra via llvm-commits]

https://github.com/artagnon created https://github.com/llvm/llvm-project/pull/193269

addActiveLaneMask asserts that the return value of a find_if is contextully convertible to true, when finding a WideCanonicalIV recipe: what it should really be checking that the iterator is not the end iterator. Fix this assert by introducing and using a variant of vputils::findUserOf.

>From 356c2b54bd76693dfd1e53f398f867cce6d7d9fd Mon Sep 17 00:00:00 2001
From: Ramkumar Ramachandra <artagnon at tenstorrent.com>
Date: Tue, 21 Apr 2026 17:49:34 +0100
Subject: [PATCH] [VPlan] Fix assert in finding WideCanIV (NFC)

addActiveLaneMask asserts that the return value of a find_if is
contextully convertible to true, when finding a WideCanonicalIV recipe:
what it should really be checking that the iterator is not the end
iterator. Fix this assert by introducing and using a variant of
vputils::findUserOf.
---
 llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp | 8 +++-----
 llvm/lib/Transforms/Vectorize/VPlanUtils.h        | 6 ++++++
 2 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
index f4a87b47cb9cd..c75c0c260c80a 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
+++ b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
@@ -3058,13 +3058,11 @@ addVPLaneMaskPhiAndUpdateExitBranch(VPlan &Plan) {
 void VPlanTransforms::addActiveLaneMask(VPlan &Plan,
                                         bool UseActiveLaneMaskForControlFlow) {
   VPRegionBlock *LoopRegion = Plan.getVectorLoopRegion();
-  auto *FoundWidenCanonicalIVUser = find_if(
-      LoopRegion->getCanonicalIV()->users(), IsaPred<VPWidenCanonicalIVRecipe>);
-  assert(FoundWidenCanonicalIVUser &&
+  auto *WideCanonicalIV = vputils::findUserOf<VPWidenCanonicalIVRecipe>(
+      LoopRegion->getCanonicalIV());
+  assert(WideCanonicalIV &&
          "Must have widened canonical IV when tail folding!");
   VPSingleDefRecipe *HeaderMask = vputils::findHeaderMask(Plan);
-  auto *WideCanonicalIV =
-      cast<VPWidenCanonicalIVRecipe>(*FoundWidenCanonicalIVUser);
   VPSingleDefRecipe *LaneMask;
   if (UseActiveLaneMaskForControlFlow) {
     LaneMask = addVPLaneMaskPhiAndUpdateExitBranch(Plan);
diff --git a/llvm/lib/Transforms/Vectorize/VPlanUtils.h b/llvm/lib/Transforms/Vectorize/VPlanUtils.h
index fd15737bfabd6..bd76b91549dc0 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanUtils.h
+++ b/llvm/lib/Transforms/Vectorize/VPlanUtils.h
@@ -130,6 +130,7 @@ inline VPRecipeBase *findRecipe(VPValue *Start, PredT Pred) {
 /// return nullptr;
 template <typename MatchT>
 static VPRecipeBase *findUserOf(VPValue *V, const MatchT &P) {
+  using namespace llvm::VPlanPatternMatch;
   auto It = find_if(V->users(), match_fn(P));
   return It == V->user_end() ? nullptr : cast<VPRecipeBase>(*It);
 }
@@ -141,6 +142,11 @@ template <unsigned Opcode> static VPInstruction *findUserOf(VPValue *V) {
   return cast_or_null<VPInstruction>(findUserOf(V, m_VPInstruction<Opcode>()));
 }
 
+template <typename RecipeTy> static RecipeTy *findUserOf(VPValue *V) {
+  using namespace llvm::VPlanPatternMatch;
+  return cast_or_null<RecipeTy>(findUserOf(V, m_Isa<RecipeTy>()));
+}
+
 /// Find the canonical IV increment of \p Plan's vector loop region. Returns
 /// nullptr if not found.
 VPInstruction *findCanonicalIVIncrement(VPlan &Plan);