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[ConstantFolding] Fold intrinsics of scalable vectors with splatted operands #141845

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Merged
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May 28, 2025
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Merged

[ConstantFolding] Fold intrinsics of scalable vectors with splatted operands #141845

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Precommit tests
lukel97 May 28, 2025
5b7d6d5
[ConstantFolding] Fold intrinsics of scalable vectors with splatted o…
lukel97 May 28, 2025
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30 changes: 29 additions & 1 deletion llvm/lib/Analysis/ConstantFolding.cpp
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Expand Up @@ -3780,7 +3780,35 @@ static Constant *ConstantFoldScalableVectorCall(
default:
break;
}
return nullptr;

// If trivially vectorizable, try folding it via the scalar call if all
// operands are splats.

// TODO: ConstantFoldFixedVectorCall should probably check this too?
if (!isTriviallyVectorizable(IntrinsicID))
return nullptr;

SmallVector<Constant *, 4> SplatOps;
for (auto [I, Op] : enumerate(Operands)) {
if (isVectorIntrinsicWithScalarOpAtArg(IntrinsicID, I, /*TTI=*/nullptr)) {
SplatOps.push_back(Op);
continue;
}
// TODO: Should getSplatValue return a poison scalar for a poison vector?
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@nikic nikic May 28, 2025

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It should...

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@lukel97 lukel97 May 28, 2025

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Will do this in a follow up, seems to be NFC?

if (isa<PoisonValue>(Op)) {
SplatOps.push_back(PoisonValue::get(Op->getType()->getScalarType()));
continue;
}
Constant *Splat = Op->getSplatValue();
if (!Splat)
return nullptr;
SplatOps.push_back(Splat);
}
Constant *Folded = ConstantFoldScalarCall(
Name, IntrinsicID, SVTy->getElementType(), SplatOps, TLI, Call);
if (!Folded)
return nullptr;
return ConstantVector::getSplat(SVTy->getElementCount(), Folded);
}

static std::pair<Constant *, Constant *>
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4 changes: 3 additions & 1 deletion llvm/lib/IR/Constants.cpp
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Expand Up @@ -1507,7 +1507,9 @@ Constant *ConstantVector::getSplat(ElementCount EC, Constant *V) {

if (V->isNullValue())
return ConstantAggregateZero::get(VTy);
else if (isa<UndefValue>(V))
if (isa<PoisonValue>(V))
return PoisonValue::get(VTy);
if (isa<UndefValue>(V))
return UndefValue::get(VTy);

Type *IdxTy = Type::getInt64Ty(VTy->getContext());
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8 changes: 8 additions & 0 deletions llvm/test/Transforms/InstSimplify/ConstProp/abs.ll
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Expand Up @@ -43,3 +43,11 @@ define <8 x i8> @vec_const() {
%r = call <8 x i8> @llvm.abs.v8i8(<8 x i8> <i8 -127, i8 -126, i8 -42, i8 -1, i8 0, i8 1, i8 42, i8 127>, i1 1)
ret <8 x i8> %r
}

define <vscale x 1 x i8> @scalable_vec_const() {
; CHECK-LABEL: @scalable_vec_const(
; CHECK-NEXT: ret <vscale x 1 x i8> splat (i8 42)
;
%r = call <vscale x 1 x i8> @llvm.abs(<vscale x 1 x i8> splat (i8 -42), i1 1)
ret <vscale x 1 x i8> %r
}
8 changes: 8 additions & 0 deletions llvm/test/Transforms/InstSimplify/ConstProp/fma.ll
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Expand Up @@ -16,6 +16,14 @@ define double @PR20832() {
ret double %1
}

define <vscale x 1 x double> @scalable_vector() {
; CHECK-LABEL: @scalable_vector(
; CHECK-NEXT: ret <vscale x 1 x double> splat (double 5.600000e+01)
;
%1 = call <vscale x 1 x double> @llvm.fma(<vscale x 1 x double> splat (double 7.0), <vscale x 1 x double> splat (double 8.0), <vscale x 1 x double> splat (double 0.0))
ret <vscale x 1 x double> %1
}

; Test builtin fma with all finite non-zero constants.
define double @test_all_finite() {
; CHECK-LABEL: @test_all_finite(
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3 changes: 1 addition & 2 deletions llvm/test/Transforms/InstSimplify/exp10.ll
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Expand Up @@ -109,8 +109,7 @@ define <2 x float> @exp10_zero_vector() {

define <vscale x 2 x float> @exp10_zero_scalable_vector() {
; CHECK-LABEL: define <vscale x 2 x float> @exp10_zero_scalable_vector() {
; CHECK-NEXT: [[RET:%.*]] = call <vscale x 2 x float> @llvm.exp10.nxv2f32(<vscale x 2 x float> zeroinitializer)
; CHECK-NEXT: ret <vscale x 2 x float> [[RET]]
; CHECK-NEXT: ret <vscale x 2 x float> splat (float 1.000000e+00)
;
%ret = call <vscale x 2 x float> @llvm.exp10.nxv2f32(<vscale x 2 x float> zeroinitializer)
ret <vscale x 2 x float> %ret
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