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[SCEV] Handle non-constant start values in AddRec UDiv canonicalization. #170474

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fhahn merged 2 commits into from
Dec 3, 2025
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[SCEV] Handle non-constant start values in AddRec UDiv canonicalization. #170474

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256aa29
[SCEV] Handle non-constant start values in AddRec UDiv canonicalization.
fhahn Dec 3, 2025
c12e092
!fixup strip outdated comment
fhahn Dec 3, 2025
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21 changes: 12 additions & 9 deletions llvm/lib/Analysis/ScalarEvolution.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -3490,11 +3490,9 @@ const SCEV *ScalarEvolution::getUDivExpr(const SCEV *LHS,
}
/// Get a canonical UDivExpr for a recurrence.
/// {X,+,N}/C => {Y,+,N}/C where Y=X-(X%N). Safe when C%N=0.
// We can currently only fold X%N if X is constant.
const SCEVConstant *StartC = dyn_cast<SCEVConstant>(AR->getStart());
if (StartC && !DivInt.urem(StepInt)) {
const APInt &StartInt = StartC->getAPInt();
const APInt &StartRem = StartInt.urem(StepInt);
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),
Expand All @@ -3507,10 +3505,15 @@ const SCEV *ScalarEvolution::getUDivExpr(const SCEV *LHS,
// all offsets in [[(X - X%N), X).
bool CanFoldWithWrap = StepInt.ule(DivInt) && // N <= C
StepInt.isPowerOf2() && DivInt.isPowerOf2();
if (StartRem != 0 && (NoWrap || CanFoldWithWrap)) {
const SCEV *NewLHS = getAddRecExpr(
getConstant(StartInt - StartRem), Step, AR->getLoop(),
NoWrap ? SCEV::FlagNW : SCEV::FlagAnyWrap);
// Only fold if the subtraction can be folded in the start
// expression.
const SCEV *NewStart =
getMinusSCEV(AR->getStart(), getConstant(*StartRem));
if (*StartRem != 0 && (NoWrap || CanFoldWithWrap) &&
!isa<SCEVAddExpr>(NewStart)) {
const SCEV *NewLHS =
getAddRecExpr(NewStart, Step, AR->getLoop(),
NoWrap ? SCEV::FlagNW : SCEV::FlagAnyWrap);
if (LHS != NewLHS) {
LHS = NewLHS;

Expand Down
16 changes: 8 additions & 8 deletions llvm/test/Analysis/ScalarEvolution/addrec-may-wrap-udiv-canonicalize.ll
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Expand Up @@ -180,27 +180,27 @@ define void @test_step2_start_outer_add_rec_step_16(i64 %n, i64 %m) {
; CHECK-NEXT: %iv.1 = add i64 %iv, 1
; CHECK-NEXT: --> {{\{\{}}1,+,16}<%outer.header>,+,2}<%loop> U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %loop: Computable, %outer.header: Variant }
; CHECK-NEXT: %div.1 = udiv i64 %iv.1, 4
; CHECK-NEXT: --> ({{\{\{}}1,+,16}<%outer.header>,+,2}<%loop> /u 4) U: [0,4611686018427387904) S: [0,4611686018427387904) Exits: <<Unknown>> LoopDispositions: { %loop: Computable, %outer.header: Variant }
; CHECK-NEXT: --> ({{\{\{}}0,+,16}<%outer.header>,+,2}<%loop> /u 4) U: [0,4611686018427387904) S: [0,4611686018427387904) Exits: <<Unknown>> LoopDispositions: { %loop: Computable, %outer.header: Variant }
; CHECK-NEXT: %iv.2 = add i64 %iv, 2
; CHECK-NEXT: --> {{\{\{}}2,+,16}<%outer.header>,+,2}<%loop> U: [0,-1) S: [-9223372036854775808,9223372036854775807) Exits: <<Unknown>> LoopDispositions: { %loop: Computable, %outer.header: Variant }
; CHECK-NEXT: %div.2 = udiv i64 %iv.2, 4
; CHECK-NEXT: --> ({{\{\{}}2,+,16}<%outer.header>,+,2}<%loop> /u 4) U: [0,4611686018427387904) S: [0,4611686018427387904) Exits: <<Unknown>> LoopDispositions: { %loop: Computable, %outer.header: Variant }
; CHECK-NEXT: %iv.3 = add i64 %iv, 3
; CHECK-NEXT: --> {{\{\{}}3,+,16}<%outer.header>,+,2}<%loop> U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %loop: Computable, %outer.header: Variant }
; CHECK-NEXT: %div.3 = udiv i64 %iv.3, 4
; CHECK-NEXT: --> ({{\{\{}}3,+,16}<%outer.header>,+,2}<%loop> /u 4) U: [0,4611686018427387904) S: [0,4611686018427387904) Exits: <<Unknown>> LoopDispositions: { %loop: Computable, %outer.header: Variant }
; CHECK-NEXT: --> ({{\{\{}}2,+,16}<%outer.header>,+,2}<%loop> /u 4) U: [0,4611686018427387904) S: [0,4611686018427387904) Exits: <<Unknown>> LoopDispositions: { %loop: Computable, %outer.header: Variant }
; CHECK-NEXT: %iv.4 = add i64 %iv, 4
; CHECK-NEXT: --> {{\{\{}}4,+,16}<%outer.header>,+,2}<%loop> U: [0,-1) S: [-9223372036854775808,9223372036854775807) Exits: <<Unknown>> LoopDispositions: { %loop: Computable, %outer.header: Variant }
; CHECK-NEXT: %div.4 = udiv i64 %iv.4, 4
; CHECK-NEXT: --> ({{\{\{}}4,+,16}<%outer.header>,+,2}<%loop> /u 4) U: [0,4611686018427387904) S: [0,4611686018427387904) Exits: <<Unknown>> LoopDispositions: { %loop: Computable, %outer.header: Variant }
; CHECK-NEXT: %iv.5 = add i64 %iv, 5
; CHECK-NEXT: --> {{\{\{}}5,+,16}<%outer.header>,+,2}<%loop> U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %loop: Computable, %outer.header: Variant }
; CHECK-NEXT: %div.5 = udiv i64 %iv.5, 4
; CHECK-NEXT: --> ({{\{\{}}5,+,16}<%outer.header>,+,2}<%loop> /u 4) U: [0,4611686018427387904) S: [0,4611686018427387904) Exits: <<Unknown>> LoopDispositions: { %loop: Computable, %outer.header: Variant }
; CHECK-NEXT: --> ({{\{\{}}4,+,16}<%outer.header>,+,2}<%loop> /u 4) U: [0,4611686018427387904) S: [0,4611686018427387904) Exits: <<Unknown>> LoopDispositions: { %loop: Computable, %outer.header: Variant }
; CHECK-NEXT: %iv.neg.1 = add i64 %iv, -1
; CHECK-NEXT: --> {{\{\{}}-1,+,16}<%outer.header>,+,2}<%loop> U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %loop: Computable, %outer.header: Variant }
; CHECK-NEXT: %div.neg.1 = udiv i64 %iv.neg.1, 4
; CHECK-NEXT: --> ({{\{\{}}-1,+,16}<%outer.header>,+,2}<%loop> /u 4) U: [0,4611686018427387904) S: [0,4611686018427387904) Exits: <<Unknown>> LoopDispositions: { %loop: Computable, %outer.header: Variant }
; CHECK-NEXT: --> ({{\{\{}}-2,+,16}<%outer.header>,+,2}<%loop> /u 4) U: [0,4611686018427387904) S: [0,4611686018427387904) Exits: <<Unknown>> LoopDispositions: { %loop: Computable, %outer.header: Variant }
; CHECK-NEXT: %div3.0 = udiv i64 %iv, 3
; CHECK-NEXT: --> ({{\{\{}}0,+,16}<%outer.header>,+,2}<%loop> /u 3) U: [0,6148914691236517205) S: [0,6148914691236517206) Exits: <<Unknown>> LoopDispositions: { %loop: Computable, %outer.header: Variant }
; CHECK-NEXT: %div3.1 = udiv i64 %iv.1, 3
Expand Down Expand Up @@ -296,27 +296,27 @@ define void @test_step2_div4_start_outer_add_rec_step_2(i64 %n, i64 %m) {
; CHECK-NEXT: %iv.1 = add i64 %iv, 1
; CHECK-NEXT: --> {{\{\{}}1,+,2}<%outer.header>,+,2}<%loop> U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %loop: Computable, %outer.header: Variant }
; CHECK-NEXT: %div.1 = udiv i64 %iv.1, 4
; CHECK-NEXT: --> ({{\{\{}}1,+,2}<%outer.header>,+,2}<%loop> /u 4) U: [0,4611686018427387904) S: [0,4611686018427387904) Exits: <<Unknown>> LoopDispositions: { %loop: Computable, %outer.header: Variant }
; CHECK-NEXT: --> ({{\{\{}}0,+,2}<%outer.header>,+,2}<%loop> /u 4) U: [0,4611686018427387904) S: [0,4611686018427387904) Exits: <<Unknown>> LoopDispositions: { %loop: Computable, %outer.header: Variant }
; CHECK-NEXT: %iv.2 = add i64 %iv, 2
; CHECK-NEXT: --> {{\{\{}}2,+,2}<%outer.header>,+,2}<%loop> U: [0,-1) S: [-9223372036854775808,9223372036854775807) Exits: <<Unknown>> LoopDispositions: { %loop: Computable, %outer.header: Variant }
; CHECK-NEXT: %div.2 = udiv i64 %iv.2, 4
; CHECK-NEXT: --> ({{\{\{}}2,+,2}<%outer.header>,+,2}<%loop> /u 4) U: [0,4611686018427387904) S: [0,4611686018427387904) Exits: <<Unknown>> LoopDispositions: { %loop: Computable, %outer.header: Variant }
; CHECK-NEXT: %iv.3 = add i64 %iv, 3
; CHECK-NEXT: --> {{\{\{}}3,+,2}<%outer.header>,+,2}<%loop> U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %loop: Computable, %outer.header: Variant }
; CHECK-NEXT: %div.3 = udiv i64 %iv.3, 4
; CHECK-NEXT: --> ({{\{\{}}3,+,2}<%outer.header>,+,2}<%loop> /u 4) U: [0,4611686018427387904) S: [0,4611686018427387904) Exits: <<Unknown>> LoopDispositions: { %loop: Computable, %outer.header: Variant }
; CHECK-NEXT: --> ({{\{\{}}2,+,2}<%outer.header>,+,2}<%loop> /u 4) U: [0,4611686018427387904) S: [0,4611686018427387904) Exits: <<Unknown>> LoopDispositions: { %loop: Computable, %outer.header: Variant }
; CHECK-NEXT: %iv.4 = add i64 %iv, 4
; CHECK-NEXT: --> {{\{\{}}4,+,2}<%outer.header>,+,2}<%loop> U: [0,-1) S: [-9223372036854775808,9223372036854775807) Exits: <<Unknown>> LoopDispositions: { %loop: Computable, %outer.header: Variant }
; CHECK-NEXT: %div.4 = udiv i64 %iv.4, 4
; CHECK-NEXT: --> ({{\{\{}}4,+,2}<%outer.header>,+,2}<%loop> /u 4) U: [0,4611686018427387904) S: [0,4611686018427387904) Exits: <<Unknown>> LoopDispositions: { %loop: Computable, %outer.header: Variant }
; CHECK-NEXT: %iv.5 = add i64 %iv, 5
; CHECK-NEXT: --> {{\{\{}}5,+,2}<%outer.header>,+,2}<%loop> U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %loop: Computable, %outer.header: Variant }
; CHECK-NEXT: %div.5 = udiv i64 %iv.5, 4
; CHECK-NEXT: --> ({{\{\{}}5,+,2}<%outer.header>,+,2}<%loop> /u 4) U: [0,4611686018427387904) S: [0,4611686018427387904) Exits: <<Unknown>> LoopDispositions: { %loop: Computable, %outer.header: Variant }
; CHECK-NEXT: --> ({{\{\{}}4,+,2}<%outer.header>,+,2}<%loop> /u 4) U: [0,4611686018427387904) S: [0,4611686018427387904) Exits: <<Unknown>> LoopDispositions: { %loop: Computable, %outer.header: Variant }
; CHECK-NEXT: %iv.neg.1 = add i64 %iv, -1
; CHECK-NEXT: --> {{\{\{}}-1,+,2}<%outer.header>,+,2}<%loop> U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %loop: Computable, %outer.header: Variant }
; CHECK-NEXT: %div.neg.1 = udiv i64 %iv.neg.1, 4
; CHECK-NEXT: --> ({{\{\{}}-1,+,2}<%outer.header>,+,2}<%loop> /u 4) U: [0,4611686018427387904) S: [0,4611686018427387904) Exits: <<Unknown>> LoopDispositions: { %loop: Computable, %outer.header: Variant }
; CHECK-NEXT: --> ({{\{\{}}-2,+,2}<%outer.header>,+,2}<%loop> /u 4) U: [0,4611686018427387904) S: [0,4611686018427387904) Exits: <<Unknown>> LoopDispositions: { %loop: Computable, %outer.header: Variant }
; CHECK-NEXT: %div3.0 = udiv i64 %iv, 3
; CHECK-NEXT: --> ({{\{\{}}0,+,2}<%outer.header>,+,2}<%loop> /u 3) U: [0,6148914691236517205) S: [0,6148914691236517206) Exits: <<Unknown>> LoopDispositions: { %loop: Computable, %outer.header: Variant }
; CHECK-NEXT: %div3.1 = udiv i64 %iv.1, 3
Expand Down
33 changes: 33 additions & 0 deletions llvm/test/Transforms/LoopVectorize/X86/uniformshift.ll
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Expand Up @@ -48,4 +48,37 @@ exit:
ret void
}

define i64 @sdiv_arg_outer_iv(ptr noalias %dst, ptr %src) {
; CHECK: 'sdiv_arg_outer_iv'
; CHECK: Cost of 0 for VF 2: CLONE ir<%div> = sdiv ir<%add.offset>, ir<8>
; CHECK: Cost of 0 for VF 4: CLONE ir<%div> = sdiv ir<%add.offset>, ir<8>
; CHECK: Cost of 0 for VF 8: CLONE ir<%div> = sdiv ir<%add.offset>, ir<8>
; CHECK: Cost of 0 for VF 16: REPLICATE ir<%div> = sdiv ir<%add.offset>, ir<8>
entry:
br label %outer.header

outer.header:
%outer.iv = phi i32 [ 0, %entry ], [ %outer.iv.next, %outer.latch ]
%offset = shl nsw i32 %outer.iv, 7
br label %loop

loop:
%iv = phi i64 [ 0, %outer.header ], [ %iv.next, %loop ]
%iv.trunc = trunc i64 %iv to i32
%add.offset = add i32 %offset, %iv.trunc
%div = sdiv i32 %add.offset, 8
%div.ext = sext i32 %div to i64
%gep.src = getelementptr i8, ptr %src, i64 %div.ext
%l = load i8, ptr %gep.src, align 1
%gep.dst = getelementptr i8, ptr %dst, i64 %iv
store i8 %l, ptr %gep.dst, align 1
%iv.next = add i64 %iv, 1
%ec = icmp eq i64 %iv, 64
br i1 %ec, label %outer.latch, label %loop

outer.latch:
%outer.iv.next = add nsw i32 %outer.iv, 1
br label %outer.header
}

attributes #0 = { "target-features"="+avx2" "tune-cpu"="alderlake" }
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