[llvm] [SCEV] Infer NUW on AR in getUDivExpr (PR #217133)

[Ramkumar Ramachandra via llvm-commits]

https://github.com/artagnon updated https://github.com/llvm/llvm-project/pull/217133

>From 42dc6c296bc078bd41eeec875e1571b33af7e1f7 Mon Sep 17 00:00:00 2001
From: Ramkumar Ramachandra <artagnon at tenstorrent.com>
Date: Wed, 19 Aug 2026 08:53:15 +0100
Subject: [PATCH] [SCEV] Infer NUW on AR in getUDivExpr

---
 llvm/lib/Analysis/ScalarEvolution.cpp | 18 +++++-------------
 1 file changed, 5 insertions(+), 13 deletions(-)

diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 1707c6c17fe23..74a7354c9d669 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -3538,11 +3538,9 @@ const SCEV *ScalarEvolution::getUDivExpr(SCEVUse LHS, SCEVUse RHS) {
           // {X,+,N}/C --> {X/C,+,N/C} if safe and N/C can be folded.
           const APInt &StepInt = Step->getAPInt();
           const APInt &DivInt = RHSC->getAPInt();
-          if (!StepInt.urem(DivInt) &&
-              getZeroExtendExpr(AR, ExtTy) ==
-              getAddRecExpr(getZeroExtendExpr(AR->getStart(), ExtTy),
-                            getZeroExtendExpr(Step, ExtTy),
-                            AR->getLoop(), SCEV::FlagAnyWrap)) {
+          bool HasNUW = hasFlags(proveNoUnsignedWrapViaInduction(AR),
+                                 SCEVNoWrapFlags::FlagNUW);
+          if (!StepInt.urem(DivInt) && HasNUW) {
             SmallVector<SCEVUse, 4> Operands;
             for (const SCEV *Op : AR->operands())
               Operands.push_back(getUDivExpr(Op, RHS));
@@ -3553,12 +3551,6 @@ const SCEV *ScalarEvolution::getUDivExpr(SCEVUse LHS, SCEVUse RHS) {
           const APInt *StartRem;
           if (!DivInt.urem(StepInt) && match(getURemExpr(AR->getStart(), Step),
                                              m_scev_APInt(StartRem))) {
-            bool NoWrap =
-                getZeroExtendExpr(AR, ExtTy) ==
-                getAddRecExpr(getZeroExtendExpr(AR->getStart(), ExtTy),
-                              getZeroExtendExpr(Step, ExtTy), AR->getLoop(),
-                              SCEV::FlagAnyWrap);
-
             // With N <= C and both N, C as powers-of-2, the transformation
             // {X,+,N}/C => {(X - X%N),+,N}/C preserves division results even
             // if wrapping occurs, as the division results remain equivalent for
@@ -3569,11 +3561,11 @@ const SCEV *ScalarEvolution::getUDivExpr(SCEVUse LHS, SCEVUse RHS) {
             // expression.
             const SCEV *NewStart =
                 getMinusSCEV(AR->getStart(), getConstant(*StartRem));
-            if (*StartRem != 0 && (NoWrap || CanFoldWithWrap) &&
+            if (*StartRem != 0 && (HasNUW || CanFoldWithWrap) &&
                 !isa<SCEVAddExpr>(NewStart)) {
               const SCEV *NewLHS =
                   getAddRecExpr(NewStart, Step, AR->getLoop(),
-                                NoWrap ? SCEV::FlagNW : SCEV::FlagAnyWrap);
+                                HasNUW ? SCEV::FlagNW : SCEV::FlagAnyWrap);
               if (LHS != NewLHS)
                 return getUDivExpr(NewLHS, RHS);
             }