[llvm] [LV] Remove EpilogueLoopVectorizationInfo::EpilogueUF (NFC). (PR #226792)

[Florian Hahn via llvm-commits]

https://github.com/fhahn created https://github.com/llvm/llvm-project/pull/226792

The epilogue vector loop is always unrolled by 1: the only construction site passes 1 and the constructor asserted it. Drop the field and use 1 directly at its users, and drop the now always 1 EpilogueUF parameter of addMinimumVectorEpilogueIterationCheck.

>From 443dcaf248eace59f28205cd0386530a2e10a08f Mon Sep 17 00:00:00 2001
From: Florian Hahn <flo at fhahn.com>
Date: Fri, 11 Sep 2026 16:05:58 +0100
Subject: [PATCH] [LV] Remove EpilogueLoopVectorizationInfo::EpilogueUF (NFC).

The epilogue vector loop is always unrolled by 1: the only construction
site passes 1 and the constructor asserted it. Drop the field and use 1
directly at its users, and drop the now always 1 EpilogueUF parameter of
addMinimumVectorEpilogueIterationCheck.
---
 .../Transforms/Vectorize/LoopVectorize.cpp    | 25 ++++++++-----------
 .../Vectorize/VPlanConstruction.cpp           |  8 +++---
 .../Transforms/Vectorize/VPlanTransforms.h    |  4 +--
 3 files changed, 16 insertions(+), 21 deletions(-)

diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
index e934fec366331..57740f9d2ef68 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -629,15 +629,11 @@ struct EpilogueLoopVectorizationInfo {
   ElementCount MainLoopVF = ElementCount::getFixed(0);
   unsigned MainLoopUF = 0;
   ElementCount EpilogueVF = ElementCount::getFixed(0);
-  unsigned EpilogueUF = 0;
   Value *VectorTripCount = nullptr;
 
   EpilogueLoopVectorizationInfo(ElementCount MVF, unsigned MUF,
-                                ElementCount EVF, unsigned EUF)
-      : MainLoopVF(MVF), MainLoopUF(MUF), EpilogueVF(EVF), EpilogueUF(EUF) {
-    assert(EUF == 1 &&
-           "A high UF for the epilogue loop is likely not beneficial.");
-  }
+                                ElementCount EVF)
+      : MainLoopVF(MVF), MainLoopUF(MUF), EpilogueVF(EVF) {}
 };
 
 /// An extension of the inner loop vectorizer that creates a skeleton for a
@@ -707,7 +703,7 @@ class EpilogueVectorizerEpilogueLoop : public InnerLoopAndEpilogueVectorizer {
                                  VPlan &MainPlan)
       : InnerLoopAndEpilogueVectorizer(OrigLoop, PSE, LI, DT, TTI, AC, EPI,
                                        Checks, Plan, EPI.EpilogueVF,
-                                       EPI.EpilogueUF),
+                                       /*UnrollFactor=*/1),
         MainPlan(MainPlan) {}
   /// Implements the interface for creating a vectorized skeleton using the
   /// *epilogue loop* strategy (i.e., the second pass of VPlan execution).
@@ -5982,7 +5978,7 @@ void EpilogueVectorizerMainLoop::printDebugTracesAtStart() {
            << "Main Loop VF:" << EPI.MainLoopVF
            << ", Main Loop UF:" << EPI.MainLoopUF
            << ", Epilogue Loop VF:" << EPI.EpilogueVF
-           << ", Epilogue Loop UF:" << EPI.EpilogueUF << "\n";
+           << ", Epilogue Loop UF:1\n";
   });
 }
 
@@ -6029,7 +6025,7 @@ void EpilogueVectorizerEpilogueLoop::printDebugTracesAtStart() {
   LLVM_DEBUG({
     dbgs() << "Create Skeleton for epilogue vectorized loop (second pass)\n"
            << "Epilogue Loop VF:" << EPI.EpilogueVF
-           << ", Epilogue Loop UF:" << EPI.EpilogueUF << "\n";
+           << ", Epilogue Loop UF:1\n";
   });
 }
 
@@ -7594,11 +7590,10 @@ static SmallVector<Instruction *> preparePlanForEpilogueVectorLoop(
   auto VScale = Config.getVScaleForTuning();
   unsigned MainLoopStep =
       estimateElementCount(EPI.MainLoopVF * EPI.MainLoopUF, VScale);
-  unsigned EpilogueLoopStep =
-      estimateElementCount(EPI.EpilogueVF * EPI.EpilogueUF, VScale);
+  unsigned EpilogueLoopStep = estimateElementCount(EPI.EpilogueVF, VScale);
   RUN_VPLAN_PASS(VPlanTransforms::addMinimumVectorEpilogueIterationCheck, Plan,
                  EPI.VectorTripCount, Plan.requiresScalarEpilogue(),
-                 EPI.EpilogueVF, EPI.EpilogueUF, MainLoopStep, EpilogueLoopStep,
+                 EPI.EpilogueVF, MainLoopStep, EpilogueLoopStep,
                  SE);
 
   return InstsToMove;
@@ -8128,11 +8123,11 @@ bool LoopVectorizePass::processLoop(Loop *L) {
     BestEpiPlan.getVectorPreheader()->setName("vec.epilog.ph");
     SmallVector<VPInstruction *> ResumeValues =
         preparePlanForMainVectorLoop(BestMainPlan, BestEpiPlan);
-    EpilogueLoopVectorizationInfo EPI(VF.Width, IC, EpilogueVF, 1);
+    EpilogueLoopVectorizationInfo EPI(VF.Width, IC, EpilogueVF);
 
     // Add minimum iteration check for the epilogue plan, followed by runtime
     // checks for the main plan.
-    LVP.addMinimumIterationCheck(BestMainPlan, EPI.EpilogueVF, EPI.EpilogueUF,
+    LVP.addMinimumIterationCheck(BestMainPlan, EPI.EpilogueVF, /*UF=*/1,
                                  ElementCount::getFixed(0));
     LVP.attachRuntimeChecks(BestMainPlan, Checks, HasBranchWeights);
     RUN_VPLAN_PASS(
@@ -8161,7 +8156,7 @@ bool LoopVectorizePass::processLoop(Loop *L) {
         *PSE.getSE(), ResumeValues);
     RUN_VPLAN_PASS(VPlanTransforms::simplifyLiveInsWithSCEV, BestEpiPlan, PSE);
     LVP.executePlan(
-        EPI.EpilogueVF, EPI.EpilogueUF, BestEpiPlan, EpilogILV, DT,
+        EPI.EpilogueVF, /*BestUF=*/1, BestEpiPlan, EpilogILV, DT,
         LoopVectorizationPlanner::EpilogueVectorizationKind::Epilogue);
     connectEpilogueVectorLoop(BestEpiPlan, DT,
                               EpilogILV.VecEpilogueIterationCountCheck,
diff --git a/llvm/lib/Transforms/Vectorize/VPlanConstruction.cpp b/llvm/lib/Transforms/Vectorize/VPlanConstruction.cpp
index 6c5f688835c15..8f462e937b00f 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanConstruction.cpp
+++ b/llvm/lib/Transforms/Vectorize/VPlanConstruction.cpp
@@ -1617,14 +1617,14 @@ void VPlanTransforms::addIterationCountCheckBlock(
 
 void VPlanTransforms::addMinimumVectorEpilogueIterationCheck(
     VPlan &Plan, Value *VectorTripCount, bool RequiresScalarEpilogue,
-    ElementCount EpilogueVF, unsigned EpilogueUF, unsigned MainLoopStep,
-    unsigned EpilogueLoopStep, ScalarEvolution &SE) {
+    ElementCount EpilogueVF, unsigned MainLoopStep, unsigned EpilogueLoopStep,
+    ScalarEvolution &SE) {
   // Add the minimum iteration check for the epilogue vector loop.
   VPValue *TC = Plan.getTripCount();
   Value *TripCount = TC->getLiveInIRValue();
   VPBuilder Builder(cast<VPBasicBlock>(Plan.getEntry()));
-  VPValue *VFxUF = Builder.createExpandSCEV(SE.getElementCount(
-      TripCount->getType(), (EpilogueVF * EpilogueUF), SCEV::FlagNUW));
+  VPValue *VFxUF = Builder.createExpandSCEV(
+      SE.getElementCount(TripCount->getType(), EpilogueVF, SCEV::FlagNUW));
   VPValue *Count = Builder.createSub(TC, Plan.getOrAddLiveIn(VectorTripCount),
                                      DebugLoc::getUnknown(), "n.vec.remaining");
 
diff --git a/llvm/lib/Transforms/Vectorize/VPlanTransforms.h b/llvm/lib/Transforms/Vectorize/VPlanTransforms.h
index fd62693d6068b..d6fa21adb63e1 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanTransforms.h
+++ b/llvm/lib/Transforms/Vectorize/VPlanTransforms.h
@@ -217,8 +217,8 @@ struct VPlanTransforms {
   /// executed.
   static void addMinimumVectorEpilogueIterationCheck(
       VPlan &Plan, Value *VectorTripCount, bool RequiresScalarEpilogue,
-      ElementCount EpilogueVF, unsigned EpilogueUF, unsigned MainLoopStep,
-      unsigned EpilogueLoopStep, ScalarEvolution &SE);
+      ElementCount EpilogueVF, unsigned MainLoopStep, unsigned EpilogueLoopStep,
+      ScalarEvolution &SE);
 
   /// Replace loops in \p Plan's flat CFG with VPRegionBlocks, turning \p Plan's
   /// flat CFG into a hierarchical CFG. For the outermost loop, also create the