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[SCEV] Always return true for isKnownToBeAPowerOfTwo for SCEVVScale #183693

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Merged
lukel97 merged 3 commits into from
Feb 27, 2026
Merged

[SCEV] Always return true for isKnownToBeAPowerOfTwo for SCEVVScale #183693

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a704e75
Precommit test
lukel97 Feb 27, 2026
40f6445
[SCEV] Always return true for isKnownToBeAPowerOfTwo for SCEVVScale
lukel97 Feb 27, 2026
0d2ea3e
Merge branch 'main' into scev/vscale-power-of-two
lukel97 Feb 27, 2026
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6 changes: 3 additions & 3 deletions llvm/lib/Analysis/ScalarEvolution.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -11111,13 +11111,13 @@ bool ScalarEvolution::isKnownNonZero(const SCEV *S) {

bool ScalarEvolution::isKnownToBeAPowerOfTwo(const SCEV *S, bool OrZero,
bool OrNegative) {
auto NonRecursive = [this, OrNegative](const SCEV *S) {
auto NonRecursive = [OrNegative](const SCEV *S) {
if (auto *C = dyn_cast<SCEVConstant>(S))
return C->getAPInt().isPowerOf2() ||
(OrNegative && C->getAPInt().isNegatedPowerOf2());

// The vscale_range indicates vscale is a power-of-two.
return isa<SCEVVScale>(S) && F.hasFnAttribute(Attribute::VScaleRange);
// vscale is a power-of-two.
return isa<SCEVVScale>(S);
};

if (NonRecursive(S))
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34 changes: 34 additions & 0 deletions llvm/test/Analysis/ScalarEvolution/trip-count-scalable-stride.ll
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Expand Up @@ -525,3 +525,37 @@ for.body: ; preds = %entry, %for.body
for.end: ; preds = %for.body, %entry
ret void
}

define void @vscale_ult_no_vscale_range(ptr nocapture %A) mustprogress {
; CHECK-LABEL: 'vscale_ult_no_vscale_range'
; CHECK-NEXT: Classifying expressions for: @vscale_ult_no_vscale_range
; CHECK-NEXT: %vscale = call i32 @llvm.vscale.i32()
; CHECK-NEXT: --> vscale U: [1,0) S: [1,0)
; CHECK-NEXT: %i.05 = phi i32 [ %add, %for.body ], [ 0, %entry ]
; CHECK-NEXT: --> {0,+,vscale}<%for.body> U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %for.body: Computable }
; CHECK-NEXT: %arrayidx = getelementptr inbounds i32, ptr %A, i32 %i.05
; CHECK-NEXT: --> {%A,+,(4 * vscale)}<%for.body> U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %for.body: Computable }
; CHECK-NEXT: %add = add i32 %i.05, %vscale
; CHECK-NEXT: --> {vscale,+,vscale}<nw><%for.body> U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %for.body: Computable }
; CHECK-NEXT: Determining loop execution counts for: @vscale_ult_no_vscale_range
; CHECK-NEXT: Loop %for.body: Unpredictable backedge-taken count.
; CHECK-NEXT: Loop %for.body: Unpredictable constant max backedge-taken count.
; CHECK-NEXT: Loop %for.body: Unpredictable symbolic max backedge-taken count.
;
entry:
%vscale = call i32 @llvm.vscale.i32()
br label %for.body

for.body: ; preds = %entry, %for.body
%i.05 = phi i32 [ %add, %for.body ], [ 0, %entry ]
%arrayidx = getelementptr inbounds i32, ptr %A, i32 %i.05
%0 = load <vscale x 4 x i32>, ptr %arrayidx, align 4
%inc = add nsw <vscale x 4 x i32> %0, splat (i32 1)
store <vscale x 4 x i32> %inc, ptr %arrayidx, align 4
%add = add i32 %i.05, %vscale
%cmp = icmp ult i32 %add, u0x00010000
br i1 %cmp, label %for.body, label %for.end

for.end: ; preds = %for.body, %entry
ret void
}
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