[llvm] [LV] Remove runtime IV overflow checks (PR #183066)

[Luke Lau via llvm-commits]

https://github.com/lukel97 updated https://github.com/llvm/llvm-project/pull/183066

>From bd21bc98af225eb2e59c19fea40c59a6ca5af234 Mon Sep 17 00:00:00 2001
From: Luke Lau <luke at igalia.com>
Date: Tue, 24 Feb 2026 22:18:53 +0800
Subject: [PATCH] [LV] Remove CheckNeededWithTailFolding from
 addMinimumIterationCheck. NFC

The IV can no longer overflow with tail folding after #183080.
---
 .../Transforms/Vectorize/LoopVectorize.cpp    |  4 +--
 .../Vectorize/VPlanConstruction.cpp           | 32 +++----------------
 .../Transforms/Vectorize/VPlanTransforms.h    | 12 +++----
 3 files changed, 12 insertions(+), 36 deletions(-)

diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
index 0fd425c23c7aa..22662abc460bb 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -8679,14 +8679,14 @@ void LoopVectorizationPlanner::attachRuntimeChecks(
 void LoopVectorizationPlanner::addMinimumIterationCheck(
     VPlan &Plan, ElementCount VF, unsigned UF,
     ElementCount MinProfitableTripCount) const {
-  const uint32_t *BranchWeigths =
+  const uint32_t *BranchWeights =
       hasBranchWeightMD(*OrigLoop->getLoopLatch()->getTerminator())
           ? &MinItersBypassWeights[0]
           : nullptr;
   VPlanTransforms::addMinimumIterationCheck(
       Plan, VF, UF, MinProfitableTripCount,
       CM.requiresScalarEpilogue(VF.isVector()), CM.foldTailByMasking(),
-      /*CheckNeededWithTailFolding=*/false, OrigLoop, BranchWeigths,
+      OrigLoop, BranchWeights,
       OrigLoop->getLoopPredecessor()->getTerminator()->getDebugLoc(), PSE);
 }
 
diff --git a/llvm/lib/Transforms/Vectorize/VPlanConstruction.cpp b/llvm/lib/Transforms/Vectorize/VPlanConstruction.cpp
index 3101b42625c53..62e3e90e75054 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanConstruction.cpp
+++ b/llvm/lib/Transforms/Vectorize/VPlanConstruction.cpp
@@ -1038,9 +1038,8 @@ void VPlanTransforms::attachCheckBlock(VPlan &Plan, Value *Cond,
 void VPlanTransforms::addMinimumIterationCheck(
     VPlan &Plan, ElementCount VF, unsigned UF,
     ElementCount MinProfitableTripCount, bool RequiresScalarEpilogue,
-    bool TailFolded, bool CheckNeededWithTailFolding, Loop *OrigLoop,
-    const uint32_t *MinItersBypassWeights, DebugLoc DL,
-    PredicatedScalarEvolution &PSE) {
+    bool TailFolded, Loop *OrigLoop, const uint32_t *MinItersBypassWeights,
+    DebugLoc DL, PredicatedScalarEvolution &PSE) {
   // Generate code to check if the loop's trip count is less than VF * UF, or
   // equal to it in case a scalar epilogue is required; this implies that the
   // vector trip count is zero. This check also covers the case where adding one
@@ -1071,30 +1070,9 @@ void VPlanTransforms::addMinimumIterationCheck(
   VPBuilder Builder(EntryVPBB);
   VPValue *TripCountCheck = Plan.getFalse();
   const SCEV *Step = GetMinTripCount();
-  if (TailFolded) {
-    if (CheckNeededWithTailFolding) {
-      // vscale is not necessarily a power-of-2, which means we cannot guarantee
-      // an overflow to zero when updating induction variables and so an
-      // additional overflow check is required before entering the vector loop.
-
-      VPValue *StepVPV = Builder.createExpandSCEV(Step);
-
-      // Get the maximum unsigned value for the type.
-      VPValue *MaxUIntTripCount =
-          Plan.getConstantInt(cast<IntegerType>(TripCountTy)->getMask());
-      VPValue *DistanceToMax =
-          Builder.createSub(MaxUIntTripCount, TripCountVPV);
-
-      // Don't execute the vector loop if (UMax - n) < (VF * UF).
-      // FIXME: Should only check VF * UF, but currently checks Step=max(VF*UF,
-      // minProfitableTripCount).
-      TripCountCheck =
-          Builder.createICmp(ICmpInst::ICMP_ULT, DistanceToMax, StepVPV, DL);
-    } else {
-      // TripCountCheck = false, folding tail implies positive vector trip
-      // count.
-    }
-  } else {
+  // TripCountCheck = false, folding tail implies positive vector trip
+  // count.
+  if (!TailFolded) {
     // TODO: Emit unconditional branch to vector preheader instead of
     // conditional branch with known condition.
     TripCount = SE.applyLoopGuards(TripCount, OrigLoop);
diff --git a/llvm/lib/Transforms/Vectorize/VPlanTransforms.h b/llvm/lib/Transforms/Vectorize/VPlanTransforms.h
index 7c5d44daf003f..f0af6360bf9e4 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanTransforms.h
+++ b/llvm/lib/Transforms/Vectorize/VPlanTransforms.h
@@ -158,13 +158,11 @@ struct VPlanTransforms {
                                                bool TailFolded);
 
   // Create a check to \p Plan to see if the vector loop should be executed.
-  static void
-  addMinimumIterationCheck(VPlan &Plan, ElementCount VF, unsigned UF,
-                           ElementCount MinProfitableTripCount,
-                           bool RequiresScalarEpilogue, bool TailFolded,
-                           bool CheckNeededWithTailFolding, Loop *OrigLoop,
-                           const uint32_t *MinItersBypassWeights, DebugLoc DL,
-                           PredicatedScalarEvolution &PSE);
+  static void addMinimumIterationCheck(
+      VPlan &Plan, ElementCount VF, unsigned UF,
+      ElementCount MinProfitableTripCount, bool RequiresScalarEpilogue,
+      bool TailFolded, Loop *OrigLoop, const uint32_t *MinItersBypassWeights,
+      DebugLoc DL, PredicatedScalarEvolution &PSE);
 
   /// Add a check to \p Plan to see if the epilogue vector loop should be
   /// executed.