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[SCEV] Check if predicate is known false for predicated AddRecs. #151134

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[SCEV] Check if predicate is known false for predicated AddRecs. #151134

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e043144
[SCEV] Check if predicate is known false for predicated AddRecs.
fhahn Jul 19, 2025
1662cbf
!fixup strip unneeded changes
fhahn Aug 12, 2025
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24 changes: 24 additions & 0 deletions llvm/lib/Analysis/ScalarEvolution.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -14952,6 +14952,30 @@ const SCEVAddRecExpr *ScalarEvolution::convertSCEVToAddRecWithPredicates(
if (!AddRec)
return nullptr;

// Check if any of the transformed predicates is known to be false. In that
// case, it doesn't make sense to convert to an predicated AddRec, as the
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Suggested change
// case, it doesn't make sense to convert to an predicated AddRec, as the
// case, it doesn't make sense to convert to a predicated AddRec, as the

// versioned loop will never execute.
for (const SCEVPredicate *Pred : TransformPreds) {
auto *WrapPred = dyn_cast<SCEVWrapPredicate>(Pred);
if (!WrapPred || WrapPred->getFlags() != SCEVWrapPredicate::IncrementNSSW)
continue;

const SCEVAddRecExpr *AddRecToCheck = WrapPred->getExpr();
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Do we need to check that the addrecs are on the same loop? Or is that already guaranteed?

const SCEV *ExitCount = getBackedgeTakenCount(AddRec->getLoop());
if (isa<SCEVCouldNotCompute>(ExitCount))
continue;

const SCEV *Step = AddRecToCheck->getStepRecurrence(*this);
if (!Step->isOne())
continue;

ExitCount = getTruncateOrSignExtend(ExitCount, Step->getType());
const SCEV *Add = getAddExpr(AddRecToCheck->getStart(), ExitCount);
if (isKnownPredicate(CmpInst::ICMP_SLT, Add, AddRecToCheck->getStart())) {
return nullptr;
}
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Omit braces.

}

// Since the transformation was successful, we can now transfer the SCEV
// predicates.
Preds.append(TransformPreds.begin(), TransformPreds.end());
Expand Down
63 changes: 54 additions & 9 deletions llvm/test/Transforms/LoopVectorize/first-order-recurrence-dead-instructions.ll
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Expand Up @@ -6,16 +6,61 @@ define i8 @recurrence_phi_with_same_incoming_values_after_simplifications(i8 %fo
; CHECK-LABEL: define i8 @recurrence_phi_with_same_incoming_values_after_simplifications(
; CHECK-SAME: i8 [[FOR_START:%.*]], ptr [[DST:%.*]]) {
; CHECK-NEXT: [[ENTRY:.*]]:
; CHECK-NEXT: br i1 false, label %[[SCALAR_PH:.*]], label %[[VECTOR_PH:.*]]
; CHECK: [[VECTOR_PH]]:
; CHECK-NEXT: [[BROADCAST_SPLATINSERT:%.*]] = insertelement <4 x i8> poison, i8 [[FOR_START]], i64 0
; CHECK-NEXT: [[BROADCAST_SPLAT:%.*]] = shufflevector <4 x i8> [[BROADCAST_SPLATINSERT]], <4 x i8> poison, <4 x i32> zeroinitializer
; CHECK-NEXT: [[TMP0:%.*]] = shufflevector <4 x i8> [[BROADCAST_SPLAT]], <4 x i8> [[BROADCAST_SPLAT]], <4 x i32> <i32 3, i32 4, i32 5, i32 6>
; CHECK-NEXT: br label %[[VECTOR_BODY:.*]]
; CHECK: [[VECTOR_BODY]]:
; CHECK-NEXT: [[INDEX:%.*]] = phi i32 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[VECTOR_BODY]] ]
; CHECK-NEXT: [[OFFSET_IDX:%.*]] = add i32 1, [[INDEX]]
; CHECK-NEXT: [[TMP1:%.*]] = add i32 [[OFFSET_IDX]], 0
; CHECK-NEXT: [[TMP2:%.*]] = add i32 [[OFFSET_IDX]], 1
; CHECK-NEXT: [[TMP3:%.*]] = add i32 [[OFFSET_IDX]], 2
; CHECK-NEXT: [[TMP4:%.*]] = add i32 [[OFFSET_IDX]], 3
; CHECK-NEXT: [[TMP5:%.*]] = add i32 [[OFFSET_IDX]], 4
; CHECK-NEXT: [[TMP6:%.*]] = add i32 [[OFFSET_IDX]], 5
; CHECK-NEXT: [[TMP7:%.*]] = add i32 [[OFFSET_IDX]], 6
; CHECK-NEXT: [[TMP8:%.*]] = add i32 [[OFFSET_IDX]], 7
; CHECK-NEXT: [[TMP9:%.*]] = getelementptr inbounds i8, ptr [[DST]], i32 [[TMP1]]
; CHECK-NEXT: [[TMP10:%.*]] = getelementptr inbounds i8, ptr [[DST]], i32 [[TMP2]]
; CHECK-NEXT: [[TMP11:%.*]] = getelementptr inbounds i8, ptr [[DST]], i32 [[TMP3]]
; CHECK-NEXT: [[TMP12:%.*]] = getelementptr inbounds i8, ptr [[DST]], i32 [[TMP4]]
; CHECK-NEXT: [[TMP13:%.*]] = getelementptr inbounds i8, ptr [[DST]], i32 [[TMP5]]
; CHECK-NEXT: [[TMP14:%.*]] = getelementptr inbounds i8, ptr [[DST]], i32 [[TMP6]]
; CHECK-NEXT: [[TMP15:%.*]] = getelementptr inbounds i8, ptr [[DST]], i32 [[TMP7]]
; CHECK-NEXT: [[TMP16:%.*]] = getelementptr inbounds i8, ptr [[DST]], i32 [[TMP8]]
; CHECK-NEXT: [[TMP17:%.*]] = extractelement <4 x i8> [[TMP0]], i32 0
; CHECK-NEXT: store i8 [[TMP17]], ptr [[TMP9]], align 1
; CHECK-NEXT: [[TMP18:%.*]] = extractelement <4 x i8> [[TMP0]], i32 1
; CHECK-NEXT: store i8 [[TMP18]], ptr [[TMP10]], align 1
; CHECK-NEXT: [[TMP19:%.*]] = extractelement <4 x i8> [[TMP0]], i32 2
; CHECK-NEXT: store i8 [[TMP19]], ptr [[TMP11]], align 1
; CHECK-NEXT: [[TMP20:%.*]] = extractelement <4 x i8> [[TMP0]], i32 3
; CHECK-NEXT: store i8 [[TMP20]], ptr [[TMP12]], align 1
; CHECK-NEXT: store i8 [[TMP17]], ptr [[TMP13]], align 1
; CHECK-NEXT: store i8 [[TMP18]], ptr [[TMP14]], align 1
; CHECK-NEXT: store i8 [[TMP19]], ptr [[TMP15]], align 1
; CHECK-NEXT: store i8 [[TMP20]], ptr [[TMP16]], align 1
; CHECK-NEXT: [[INDEX_NEXT]] = add nuw i32 [[INDEX]], 8
; CHECK-NEXT: [[TMP21:%.*]] = icmp eq i32 [[INDEX_NEXT]], -8
; CHECK-NEXT: br i1 [[TMP21]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP0:![0-9]+]]
; CHECK: [[MIDDLE_BLOCK]]:
; CHECK-NEXT: br label %[[SCALAR_PH]]
; CHECK: [[SCALAR_PH]]:
; CHECK-NEXT: [[BC_RESUME_VAL:%.*]] = phi i32 [ -7, %[[MIDDLE_BLOCK]] ], [ 1, %[[ENTRY]] ]
; CHECK-NEXT: [[SCALAR_RECUR_INIT:%.*]] = phi i8 [ [[FOR_START]], %[[MIDDLE_BLOCK]] ], [ [[FOR_START]], %[[ENTRY]] ]
; CHECK-NEXT: br label %[[LOOP:.*]]
; CHECK: [[LOOP]]:
; CHECK-NEXT: [[IV:%.*]] = phi i32 [ 1, %[[ENTRY]] ], [ [[IV_NEXT:%.*]], %[[LOOP]] ]
; CHECK-NEXT: [[FOR:%.*]] = phi i8 [ [[FOR_START]], %[[ENTRY]] ], [ [[FOR_NEXT:%.*]], %[[LOOP]] ]
; CHECK-NEXT: [[IV:%.*]] = phi i32 [ [[BC_RESUME_VAL]], %[[SCALAR_PH]] ], [ [[IV_NEXT:%.*]], %[[LOOP]] ]
; CHECK-NEXT: [[FOR:%.*]] = phi i8 [ [[SCALAR_RECUR_INIT]], %[[SCALAR_PH]] ], [ [[FOR_NEXT:%.*]], %[[LOOP]] ]
; CHECK-NEXT: [[FOR_NEXT]] = and i8 [[FOR_START]], -1
; CHECK-NEXT: [[IV_NEXT]] = add i32 [[IV]], 1
; CHECK-NEXT: [[GEP_DST:%.*]] = getelementptr inbounds i8, ptr [[DST]], i32 [[IV]]
; CHECK-NEXT: store i8 [[FOR]], ptr [[GEP_DST]], align 1
; CHECK-NEXT: [[EC:%.*]] = icmp eq i32 [[IV_NEXT]], 0
; CHECK-NEXT: br i1 [[EC]], label %[[EXIT:.*]], label %[[LOOP]]
; CHECK-NEXT: br i1 [[EC]], label %[[EXIT:.*]], label %[[LOOP]], !llvm.loop [[LOOP3:![0-9]+]]
; CHECK: [[EXIT]]:
; CHECK-NEXT: [[FOR_NEXT_LCSSA:%.*]] = phi i8 [ [[FOR_NEXT]], %[[LOOP]] ]
; CHECK-NEXT: ret i8 [[FOR_NEXT_LCSSA]]
Expand Down Expand Up @@ -61,7 +106,7 @@ define i32 @sink_after_dead_inst(ptr %A.ptr) {
; CHECK-NEXT: [[INDEX_NEXT]] = add nuw i32 [[INDEX]], 8
; CHECK-NEXT: [[VEC_IND_NEXT]] = add <4 x i16> [[STEP_ADD]], splat (i16 4)
; CHECK-NEXT: [[TMP6:%.*]] = icmp eq i32 [[INDEX_NEXT]], 16
; CHECK-NEXT: br i1 [[TMP6]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP0:![0-9]+]]
; CHECK-NEXT: br i1 [[TMP6]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP4:![0-9]+]]
; CHECK: [[MIDDLE_BLOCK]]:
; CHECK-NEXT: [[VECTOR_RECUR_EXTRACT_FOR_PHI:%.*]] = extractelement <4 x i32> [[TMP2]], i32 2
; CHECK-NEXT: br label %[[FOR_END:.*]]
Expand All @@ -82,7 +127,7 @@ define i32 @sink_after_dead_inst(ptr %A.ptr) {
; CHECK-NEXT: [[EXT:%.*]] = zext i1 [[B3]] to i32
; CHECK-NEXT: [[A_GEP:%.*]] = getelementptr i32, ptr [[A_PTR]], i16 [[IV]]
; CHECK-NEXT: store i32 0, ptr [[A_GEP]], align 4
; CHECK-NEXT: br i1 [[VEC_DEAD]], label %[[FOR_END]], label %[[LOOP]], !llvm.loop [[LOOP3:![0-9]+]]
; CHECK-NEXT: br i1 [[VEC_DEAD]], label %[[FOR_END]], label %[[LOOP]], !llvm.loop [[LOOP5:![0-9]+]]
; CHECK: [[FOR_END]]:
; CHECK-NEXT: [[FOR_LCSSA:%.*]] = phi i32 [ [[FOR]], %[[LOOP]] ], [ [[VECTOR_RECUR_EXTRACT_FOR_PHI]], %[[MIDDLE_BLOCK]] ]
; CHECK-NEXT: ret i32 [[FOR_LCSSA]]
Expand Down Expand Up @@ -142,7 +187,7 @@ define void @sink_dead_inst(ptr %a) {
; CHECK-NEXT: [[INDEX_NEXT]] = add nuw i32 [[INDEX]], 8
; CHECK-NEXT: [[VEC_IND_NEXT]] = add <4 x i16> [[STEP_ADD]], splat (i16 4)
; CHECK-NEXT: [[TMP12:%.*]] = icmp eq i32 [[INDEX_NEXT]], 40
; CHECK-NEXT: br i1 [[TMP12]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP4:![0-9]+]]
; CHECK-NEXT: br i1 [[TMP12]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP6:![0-9]+]]
; CHECK: [[MIDDLE_BLOCK]]:
; CHECK-NEXT: [[VECTOR_RECUR_EXTRACT:%.*]] = extractelement <4 x i16> [[TMP4]], i32 3
; CHECK-NEXT: [[VECTOR_RECUR_EXTRACT1:%.*]] = extractelement <4 x i32> [[TMP2]], i32 3
Expand All @@ -163,7 +208,7 @@ define void @sink_dead_inst(ptr %a) {
; CHECK-NEXT: [[REC_1_PREV]] = add i16 [[IV_NEXT]], 5
; CHECK-NEXT: [[GEP:%.*]] = getelementptr i16, ptr [[A]], i16 [[IV]]
; CHECK-NEXT: store i16 [[USE_REC_1]], ptr [[GEP]], align 2
; CHECK-NEXT: br i1 [[CMP]], label %[[FOR_END:.*]], label %[[FOR_COND]], !llvm.loop [[LOOP5:![0-9]+]]
; CHECK-NEXT: br i1 [[CMP]], label %[[FOR_END:.*]], label %[[FOR_COND]], !llvm.loop [[LOOP7:![0-9]+]]
; CHECK: [[FOR_END]]:
; CHECK-NEXT: ret void
;
Expand Down Expand Up @@ -205,7 +250,7 @@ define void @unused_recurrence(ptr %a) {
; CHECK-NEXT: [[INDEX_NEXT]] = add nuw i32 [[INDEX]], 8
; CHECK-NEXT: [[VEC_IND_NEXT]] = add <4 x i16> [[STEP_ADD]], splat (i16 4)
; CHECK-NEXT: [[TMP2:%.*]] = icmp eq i32 [[INDEX_NEXT]], 1024
; CHECK-NEXT: br i1 [[TMP2]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP6:![0-9]+]]
; CHECK-NEXT: br i1 [[TMP2]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP8:![0-9]+]]
; CHECK: [[MIDDLE_BLOCK]]:
; CHECK-NEXT: [[VECTOR_RECUR_EXTRACT:%.*]] = extractelement <4 x i16> [[TMP1]], i32 3
; CHECK-NEXT: br label %[[SCALAR_PH]]
Expand All @@ -220,7 +265,7 @@ define void @unused_recurrence(ptr %a) {
; CHECK-NEXT: [[IV_NEXT]] = add i16 [[IV]], 1
; CHECK-NEXT: [[REC_1_PREV]] = add i16 [[IV_NEXT]], 5
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i16 [[IV]], 1000
; CHECK-NEXT: br i1 [[CMP]], label %[[FOR_END:.*]], label %[[FOR_COND]], !llvm.loop [[LOOP7:![0-9]+]]
; CHECK-NEXT: br i1 [[CMP]], label %[[FOR_END:.*]], label %[[FOR_COND]], !llvm.loop [[LOOP9:![0-9]+]]
; CHECK: [[FOR_END]]:
; CHECK-NEXT: ret void
;
Expand Down
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