diff --git a/llvm/include/llvm/Transforms/Utils/ScalarEvolutionExpander.h b/llvm/include/llvm/Transforms/Utils/ScalarEvolutionExpander.h
index 035705b7f4b78..fa10443f14bb7 100644
--- a/llvm/include/llvm/Transforms/Utils/ScalarEvolutionExpander.h
+++ b/llvm/include/llvm/Transforms/Utils/ScalarEvolutionExpander.h
@@ -258,6 +258,14 @@ class SCEVExpander : public SCEVVisitor<SCEVExpander, Value *> {
bool hoistIVInc(Instruction *IncV, Instruction *InsertPos,
bool RecomputePoisonFlags = false);
+ /// Return true if both increments directly increment the corresponding IV PHI
+ /// nodes and have the same opcode. It is not safe to re-use the flags from
+ /// the original increment, if it is more complex and SCEV expansion may have
+ /// yielded a more simplified wider increment.
+ static bool canReuseFlagsFromOriginalIVInc(PHINode *OrigPhi, PHINode *WidePhi,
+ Instruction *OrigInc,
+ Instruction *WideInc);
+
/// replace congruent phis with their most canonical representative. Return
/// the number of phis eliminated.
unsigned replaceCongruentIVs(Loop *L, const DominatorTree *DT,
diff --git a/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp b/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
index 3a28909473d95..fbe1dba5b8d4e 100644
--- a/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
+++ b/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
@@ -771,6 +771,15 @@ bool SCEVExpander::hoistIVInc(Instruction *IncV, Instruction *InsertPos,
return true;
}
+bool SCEVExpander::canReuseFlagsFromOriginalIVInc(PHINode *OrigPhi,
+ PHINode *WidePhi,
+ Instruction *OrigInc,
+ Instruction *WideInc) {
+ return match(OrigInc, m_c_BinOp(m_Specific(OrigPhi), m_Value())) &&
+ match(WideInc, m_c_BinOp(m_Specific(WidePhi), m_Value())) &&
+ OrigInc->getOpcode() == WideInc->getOpcode();
+}
+
/// Determine if this cyclic phi is in a form that would have been generated by
/// LSR. We don't care if the phi was actually expanded in this pass, as long
/// as it is in a low-cost form, for example, no implied multiplication. This
diff --git a/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp b/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
index 5aa6df49e7f67..66bba1ca2f1d7 100644
--- a/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
@@ -1131,7 +1131,8 @@ class WidenIV {
const SCEV *getSCEVByOpCode(const SCEV *LHS, const SCEV *RHS,
unsigned OpCode) const;
- Instruction *widenIVUse(NarrowIVDefUse DU, SCEVExpander &Rewriter);
+ Instruction *widenIVUse(NarrowIVDefUse DU, SCEVExpander &Rewriter,
+ PHINode *OrigPhi, PHINode *WidePhi);
bool widenLoopCompare(NarrowIVDefUse DU);
bool widenWithVariantUse(NarrowIVDefUse DU);
@@ -1731,7 +1732,9 @@ bool WidenIV::widenWithVariantUse(WidenIV::NarrowIVDefUse DU) {
/// Determine whether an individual user of the narrow IV can be widened. If so,
/// return the wide clone of the user.
-Instruction *WidenIV::widenIVUse(WidenIV::NarrowIVDefUse DU, SCEVExpander &Rewriter) {
+Instruction *WidenIV::widenIVUse(WidenIV::NarrowIVDefUse DU,
+ SCEVExpander &Rewriter, PHINode *OrigPhi,
+ PHINode *WidePhi) {
assert(ExtendKindMap.count(DU.NarrowDef) &&
"Should already know the kind of extension used to widen NarrowDef");
@@ -1825,11 +1828,18 @@ Instruction *WidenIV::widenIVUse(WidenIV::NarrowIVDefUse DU, SCEVExpander &Rewri
if (!WideAddRec.first)
return nullptr;
- // Reuse the IV increment that SCEVExpander created as long as it dominates
- // NarrowUse.
+ // Reuse the IV increment that SCEVExpander created. Recompute flags, unless
+ // the flags for both increments agree and it is safe to use the ones from
+ // the original inc. In that case, the new use of the wide increment won't
+ // be more poisonous.
+ bool NeedToRecomputeFlags =
+ !SCEVExpander::canReuseFlagsFromOriginalIVInc(OrigPhi, WidePhi,
+ DU.NarrowUse, WideInc) ||
+ DU.NarrowUse->hasNoUnsignedWrap() != WideInc->hasNoUnsignedWrap() ||
+ DU.NarrowUse->hasNoSignedWrap() != WideInc->hasNoSignedWrap();
Instruction *WideUse = nullptr;
if (WideAddRec.first == WideIncExpr &&
- Rewriter.hoistIVInc(WideInc, DU.NarrowUse))
+ Rewriter.hoistIVInc(WideInc, DU.NarrowUse, NeedToRecomputeFlags))
WideUse = WideInc;
else {
WideUse = cloneIVUser(DU, WideAddRec.first);
@@ -1996,11 +2006,9 @@ PHINode *WidenIV::createWideIV(SCEVExpander &Rewriter) {
// the same opcode. It is not safe to re-use the flags from the original
// increment, if it is more complex and SCEV expansion may have yielded a
// more simplified wider increment.
- bool MatchingOps =
- match(OrigInc, m_c_BinOp(m_Specific(OrigPhi), m_Value())) &&
- match(WideInc, m_c_BinOp(m_Specific(WidePhi), m_Value())) &&
- OrigInc->getOpcode() == WideInc->getOpcode();
- if (MatchingOps && isa<OverflowingBinaryOperator>(OrigInc) &&
+ if (SCEVExpander::canReuseFlagsFromOriginalIVInc(OrigPhi, WidePhi,
+ OrigInc, WideInc) &&
+ isa<OverflowingBinaryOperator>(OrigInc) &&
isa<OverflowingBinaryOperator>(WideInc)) {
WideInc->setHasNoUnsignedWrap(WideInc->hasNoUnsignedWrap() ||
OrigInc->hasNoUnsignedWrap());
@@ -2024,7 +2032,7 @@ PHINode *WidenIV::createWideIV(SCEVExpander &Rewriter) {
// Process a def-use edge. This may replace the use, so don't hold a
// use_iterator across it.
- Instruction *WideUse = widenIVUse(DU, Rewriter);
+ Instruction *WideUse = widenIVUse(DU, Rewriter, OrigPhi, WidePhi);
// Follow all def-use edges from the previous narrow use.
if (WideUse)
diff --git a/llvm/test/Transforms/IndVarSimplify/hoist-wide-inc-for-narrow-use-recompute-flags.ll b/llvm/test/Transforms/IndVarSimplify/hoist-wide-inc-for-narrow-use-recompute-flags.ll
index ddb3890f3bb36..cc99ee312ccb7 100644
--- a/llvm/test/Transforms/IndVarSimplify/hoist-wide-inc-for-narrow-use-recompute-flags.ll
+++ b/llvm/test/Transforms/IndVarSimplify/hoist-wide-inc-for-narrow-use-recompute-flags.ll
@@ -4,7 +4,7 @@
target datalayout = "e-m:o-i64:64-i128:128-n32:64-S128"
; Test for https://github.com/llvm/llvm-project/issues/82243.
-; FIXME: Currently no-wrap flags on hoisted wide IV are not dropped properly.
+; Check that NUW flag on hoisted wide IV is dropped properly.
define void @test_pr82243(ptr %f) {
; CHECK-LABEL: define void @test_pr82243(
; CHECK-SAME: ptr [[F:%.*]]) {
@@ -14,7 +14,7 @@ define void @test_pr82243(ptr %f) {
; CHECK-NEXT: [[INDVARS_IV:%.*]] = phi i64 [ [[INDVARS_IV_NEXT:%.*]], [[OUTER_LATCH:%.*]] ], [ 1, [[ENTRY:%.*]] ]
; CHECK-NEXT: [[GEP_IV_EXT:%.*]] = getelementptr i32, ptr [[F]], i64 [[INDVARS_IV]]
; CHECK-NEXT: store i32 1, ptr [[GEP_IV_EXT]], align 4
-; CHECK-NEXT: [[INDVARS_IV_NEXT]] = add nuw nsw i64 [[INDVARS_IV]], -1
+; CHECK-NEXT: [[INDVARS_IV_NEXT]] = add nsw i64 [[INDVARS_IV]], -1
; CHECK-NEXT: [[TMP0:%.*]] = trunc i64 [[INDVARS_IV_NEXT]] to i32
; CHECK-NEXT: [[SHL:%.*]] = shl i32 123, [[TMP0]]
; CHECK-NEXT: [[GEP_SHL:%.*]] = getelementptr i32, ptr [[F]], i32 [[SHL]]