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[LLVM][ConstantFolding] Extend constantFoldVectorReduce to include scalable vectors. #165437

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Oct 31, 2025
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[LLVM][ConstantFolding] Extend constantFoldVectorReduce to include scalable vectors. #165437

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3538605
[LLVM][ConstantFolding] Extend constantFoldVectorReduce to include sc…
paulwalker-arm Oct 27, 2025
4da9437
Remove unnecessary isa<Posion> check. Add support for vec.reduce.mul.…
paulwalker-arm Oct 29, 2025
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39 changes: 30 additions & 9 deletions llvm/lib/Analysis/ConstantFolding.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2163,18 +2163,39 @@ Constant *ConstantFoldBinaryFP(double (*NativeFP)(double, double),
}

Constant *constantFoldVectorReduce(Intrinsic::ID IID, Constant *Op) {
FixedVectorType *VT = dyn_cast<FixedVectorType>(Op->getType());
if (!VT)
return nullptr;

// This isn't strictly necessary, but handle the special/common case of zero:
// all integer reductions of a zero input produce zero.
if (isa<ConstantAggregateZero>(Op))
return ConstantInt::get(VT->getElementType(), 0);
auto *OpVT = cast<VectorType>(Op->getType());

// This is the same as the underlying binops - poison propagates.
if (isa<PoisonValue>(Op) || Op->containsPoisonElement())
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@david-arm david-arm Oct 29, 2025

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Interestingly, containsUndefinedElement doesn't try as hard as it could to find poison values in scalable vectors. For example, it could check if there is an insert of poison somewhere.

This is just an observation - no expectation from you to do anything!

However, it looks like the additional call to isa<PoisonValue>(Op) is redundant since containsPoisonElement asks the same question. Since you're here perhaps worth removing?

return PoisonValue::get(VT->getElementType());
return PoisonValue::get(OpVT->getElementType());

// Shortcut non-accumulating reductions.
if (Constant *SplatVal = Op->getSplatValue()) {
switch (IID) {
case Intrinsic::vector_reduce_and:
case Intrinsic::vector_reduce_or:
case Intrinsic::vector_reduce_smin:
case Intrinsic::vector_reduce_smax:
case Intrinsic::vector_reduce_umin:
case Intrinsic::vector_reduce_umax:
return SplatVal;
case Intrinsic::vector_reduce_add:
case Intrinsic::vector_reduce_mul:
if (SplatVal->isZeroValue())
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@david-arm david-arm Oct 29, 2025

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In theory you can also do a short cut for a mul reduce with a splat value of 1, if you think it's worth adding?

return SplatVal;
break;
case Intrinsic::vector_reduce_xor:
if (SplatVal->isZeroValue())
return SplatVal;
if (OpVT->getElementCount().isKnownMultipleOf(2))
return Constant::getNullValue(OpVT->getElementType());
break;
}
}

FixedVectorType *VT = dyn_cast<FixedVectorType>(OpVT);
if (!VT)
return nullptr;

// TODO: Handle undef.
auto *EltC = dyn_cast_or_null<ConstantInt>(Op->getAggregateElement(0U));
Expand Down
84 changes: 34 additions & 50 deletions llvm/test/Transforms/InstSimplify/ConstProp/vecreduce.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -12,8 +12,7 @@ define i32 @add_0() {

define i32 @add_0_scalable_vector() {
; CHECK-LABEL: @add_0_scalable_vector(
; CHECK-NEXT: [[X:%.*]] = call i32 @llvm.vector.reduce.add.nxv8i32(<vscale x 8 x i32> zeroinitializer)
; CHECK-NEXT: ret i32 [[X]]
; CHECK-NEXT: ret i32 0
;
%x = call i32 @llvm.vector.reduce.add.nxv8i32(<vscale x 8 x i32> zeroinitializer)
ret i32 %x
Expand Down Expand Up @@ -89,8 +88,7 @@ define i32 @add_poison() {

define i32 @add_poison_scalable_vector() {
; CHECK-LABEL: @add_poison_scalable_vector(
; CHECK-NEXT: [[X:%.*]] = call i32 @llvm.vector.reduce.add.nxv8i32(<vscale x 8 x i32> poison)
; CHECK-NEXT: ret i32 [[X]]
; CHECK-NEXT: ret i32 poison
;
%x = call i32 @llvm.vector.reduce.add.nxv8i32(<vscale x 8 x i32> poison)
ret i32 %x
Expand Down Expand Up @@ -123,8 +121,7 @@ define i32 @mul_0() {

define i32 @mul_0_scalable_vector() {
; CHECK-LABEL: @mul_0_scalable_vector(
; CHECK-NEXT: [[X:%.*]] = call i32 @llvm.vector.reduce.mul.nxv8i32(<vscale x 8 x i32> zeroinitializer)
; CHECK-NEXT: ret i32 [[X]]
; CHECK-NEXT: ret i32 0
;
%x = call i32 @llvm.vector.reduce.mul.nxv8i32(<vscale x 8 x i32> zeroinitializer)
ret i32 %x
Expand Down Expand Up @@ -200,8 +197,7 @@ define i32 @mul_poison() {

define i32 @mul_poison_scalable_vector() {
; CHECK-LABEL: @mul_poison_scalable_vector(
; CHECK-NEXT: [[X:%.*]] = call i32 @llvm.vector.reduce.mul.nxv8i32(<vscale x 8 x i32> poison)
; CHECK-NEXT: ret i32 [[X]]
; CHECK-NEXT: ret i32 poison
;
%x = call i32 @llvm.vector.reduce.mul.nxv8i32(<vscale x 8 x i32> poison)
ret i32 %x
Expand All @@ -225,8 +221,7 @@ define i32 @and_0() {

define i32 @and_0_scalable_vector() {
; CHECK-LABEL: @and_0_scalable_vector(
; CHECK-NEXT: [[X:%.*]] = call i32 @llvm.vector.reduce.and.nxv8i32(<vscale x 8 x i32> zeroinitializer)
; CHECK-NEXT: ret i32 [[X]]
; CHECK-NEXT: ret i32 0
;
%x = call i32 @llvm.vector.reduce.and.nxv8i32(<vscale x 8 x i32> zeroinitializer)
ret i32 %x
Expand All @@ -242,8 +237,7 @@ define i32 @and_1() {

define i32 @and_1_scalable_vector() {
; CHECK-LABEL: @and_1_scalable_vector(
; CHECK-NEXT: [[X:%.*]] = call i32 @llvm.vector.reduce.and.nxv8i32(<vscale x 8 x i32> splat (i32 1))
; CHECK-NEXT: ret i32 [[X]]
; CHECK-NEXT: ret i32 1
;
%x = call i32 @llvm.vector.reduce.and.nxv8i32(<vscale x 8 x i32> splat (i32 1))
ret i32 %x
Expand Down Expand Up @@ -302,8 +296,7 @@ define i32 @and_poison() {

define i32 @and_poison_scalable_vector() {
; CHECK-LABEL: @and_poison_scalable_vector(
; CHECK-NEXT: [[X:%.*]] = call i32 @llvm.vector.reduce.and.nxv8i32(<vscale x 8 x i32> poison)
; CHECK-NEXT: ret i32 [[X]]
; CHECK-NEXT: ret i32 poison
;
%x = call i32 @llvm.vector.reduce.and.nxv8i32(<vscale x 8 x i32> poison)
ret i32 %x
Expand All @@ -327,8 +320,7 @@ define i32 @or_0() {

define i32 @or_0_scalable_vector() {
; CHECK-LABEL: @or_0_scalable_vector(
; CHECK-NEXT: [[X:%.*]] = call i32 @llvm.vector.reduce.or.nxv8i32(<vscale x 8 x i32> zeroinitializer)
; CHECK-NEXT: ret i32 [[X]]
; CHECK-NEXT: ret i32 0
;
%x = call i32 @llvm.vector.reduce.or.nxv8i32(<vscale x 8 x i32> zeroinitializer)
ret i32 %x
Expand All @@ -344,8 +336,7 @@ define i32 @or_1() {

define i32 @or_1_scalable_vector() {
; CHECK-LABEL: @or_1_scalable_vector(
; CHECK-NEXT: [[X:%.*]] = call i32 @llvm.vector.reduce.or.nxv8i32(<vscale x 8 x i32> splat (i32 1))
; CHECK-NEXT: ret i32 [[X]]
; CHECK-NEXT: ret i32 1
;
%x = call i32 @llvm.vector.reduce.or.nxv8i32(<vscale x 8 x i32> splat (i32 1))
ret i32 %x
Expand Down Expand Up @@ -404,8 +395,7 @@ define i32 @or_poison() {

define i32 @or_poison_scalable_vector() {
; CHECK-LABEL: @or_poison_scalable_vector(
; CHECK-NEXT: [[X:%.*]] = call i32 @llvm.vector.reduce.or.nxv8i32(<vscale x 8 x i32> poison)
; CHECK-NEXT: ret i32 [[X]]
; CHECK-NEXT: ret i32 poison
;
%x = call i32 @llvm.vector.reduce.or.nxv8i32(<vscale x 8 x i32> poison)
ret i32 %x
Expand All @@ -429,8 +419,7 @@ define i32 @xor_0() {

define i32 @xor_0_scalable_vector() {
; CHECK-LABEL: @xor_0_scalable_vector(
; CHECK-NEXT: [[X:%.*]] = call i32 @llvm.vector.reduce.xor.nxv8i32(<vscale x 8 x i32> zeroinitializer)
; CHECK-NEXT: ret i32 [[X]]
; CHECK-NEXT: ret i32 0
;
%x = call i32 @llvm.vector.reduce.xor.nxv8i32(<vscale x 8 x i32> zeroinitializer)
ret i32 %x
Expand All @@ -446,13 +435,21 @@ define i32 @xor_1() {

define i32 @xor_1_scalable_vector() {
; CHECK-LABEL: @xor_1_scalable_vector(
; CHECK-NEXT: [[X:%.*]] = call i32 @llvm.vector.reduce.xor.nxv8i32(<vscale x 8 x i32> splat (i32 1))
; CHECK-NEXT: ret i32 [[X]]
; CHECK-NEXT: ret i32 0
;
%x = call i32 @llvm.vector.reduce.xor.nxv8i32(<vscale x 8 x i32> splat(i32 1))
ret i32 %x
}

define i32 @xor_1_scalable_vector_lane_count_not_known_even() {
; CHECK-LABEL: @xor_1_scalable_vector_lane_count_not_known_even(
; CHECK-NEXT: [[X:%.*]] = call i32 @llvm.vector.reduce.xor.nxv1i32(<vscale x 1 x i32> splat (i32 1))
; CHECK-NEXT: ret i32 [[X]]
;
%x = call i32 @llvm.vector.reduce.xor.nxv8i32(<vscale x 1 x i32> splat(i32 1))
ret i32 %x
}

define i32 @xor_inc() {
; CHECK-LABEL: @xor_inc(
; CHECK-NEXT: ret i32 10
Expand Down Expand Up @@ -506,8 +503,7 @@ define i32 @xor_poison() {

define i32 @xor_poison_scalable_vector() {
; CHECK-LABEL: @xor_poison_scalable_vector(
; CHECK-NEXT: [[X:%.*]] = call i32 @llvm.vector.reduce.xor.nxv8i32(<vscale x 8 x i32> poison)
; CHECK-NEXT: ret i32 [[X]]
; CHECK-NEXT: ret i32 poison
;
%x = call i32 @llvm.vector.reduce.xor.nxv8i32(<vscale x 8 x i32> poison)
ret i32 %x
Expand All @@ -531,8 +527,7 @@ define i32 @smin_0() {

define i32 @smin_0_scalable_vector() {
; CHECK-LABEL: @smin_0_scalable_vector(
; CHECK-NEXT: [[X:%.*]] = call i32 @llvm.vector.reduce.smin.nxv8i32(<vscale x 8 x i32> zeroinitializer)
; CHECK-NEXT: ret i32 [[X]]
; CHECK-NEXT: ret i32 0
;
%x = call i32 @llvm.vector.reduce.smin.nxv8i32(<vscale x 8 x i32> zeroinitializer)
ret i32 %x
Expand All @@ -548,8 +543,7 @@ define i32 @smin_1() {

define i32 @smin_1_scalable_vector() {
; CHECK-LABEL: @smin_1_scalable_vector(
; CHECK-NEXT: [[X:%.*]] = call i32 @llvm.vector.reduce.smin.nxv8i32(<vscale x 8 x i32> splat (i32 1))
; CHECK-NEXT: ret i32 [[X]]
; CHECK-NEXT: ret i32 1
;
%x = call i32 @llvm.vector.reduce.smin.nxv8i32(<vscale x 8 x i32> splat(i32 1))
ret i32 %x
Expand Down Expand Up @@ -608,8 +602,7 @@ define i32 @smin_poison() {

define i32 @smin_poison_scalable_vector() {
; CHECK-LABEL: @smin_poison_scalable_vector(
; CHECK-NEXT: [[X:%.*]] = call i32 @llvm.vector.reduce.smin.nxv8i32(<vscale x 8 x i32> poison)
; CHECK-NEXT: ret i32 [[X]]
; CHECK-NEXT: ret i32 poison
;
%x = call i32 @llvm.vector.reduce.smin.nxv8i32(<vscale x 8 x i32> poison)
ret i32 %x
Expand All @@ -633,8 +626,7 @@ define i32 @smax_0() {

define i32 @smax_0_scalable_vector() {
; CHECK-LABEL: @smax_0_scalable_vector(
; CHECK-NEXT: [[X:%.*]] = call i32 @llvm.vector.reduce.smax.nxv8i32(<vscale x 8 x i32> zeroinitializer)
; CHECK-NEXT: ret i32 [[X]]
; CHECK-NEXT: ret i32 0
;
%x = call i32 @llvm.vector.reduce.smax.nxv8i32(<vscale x 8 x i32> zeroinitializer)
ret i32 %x
Expand All @@ -650,8 +642,7 @@ define i32 @smax_1() {

define i32 @smax_1_scalable_vector() {
; CHECK-LABEL: @smax_1_scalable_vector(
; CHECK-NEXT: [[X:%.*]] = call i32 @llvm.vector.reduce.smax.nxv8i32(<vscale x 8 x i32> splat (i32 1))
; CHECK-NEXT: ret i32 [[X]]
; CHECK-NEXT: ret i32 1
;
%x = call i32 @llvm.vector.reduce.smax.nxv8i32(<vscale x 8 x i32> splat(i32 1))
ret i32 %x
Expand Down Expand Up @@ -710,8 +701,7 @@ define i32 @smax_poison() {

define i32 @smax_poison_scalable_vector() {
; CHECK-LABEL: @smax_poison_scalable_vector(
; CHECK-NEXT: [[X:%.*]] = call i32 @llvm.vector.reduce.smax.nxv8i32(<vscale x 8 x i32> poison)
; CHECK-NEXT: ret i32 [[X]]
; CHECK-NEXT: ret i32 poison
;
%x = call i32 @llvm.vector.reduce.smax.nxv8i32(<vscale x 8 x i32> poison)
ret i32 %x
Expand All @@ -735,8 +725,7 @@ define i32 @umin_0() {

define i32 @umin_0_scalable_vector() {
; CHECK-LABEL: @umin_0_scalable_vector(
; CHECK-NEXT: [[X:%.*]] = call i32 @llvm.vector.reduce.umin.nxv8i32(<vscale x 8 x i32> zeroinitializer)
; CHECK-NEXT: ret i32 [[X]]
; CHECK-NEXT: ret i32 0
;
%x = call i32 @llvm.vector.reduce.umin.nxv8i32(<vscale x 8 x i32> zeroinitializer)
ret i32 %x
Expand All @@ -752,8 +741,7 @@ define i32 @umin_1() {

define i32 @umin_1_scalable_vector() {
; CHECK-LABEL: @umin_1_scalable_vector(
; CHECK-NEXT: [[X:%.*]] = call i32 @llvm.vector.reduce.umin.nxv8i32(<vscale x 8 x i32> splat (i32 1))
; CHECK-NEXT: ret i32 [[X]]
; CHECK-NEXT: ret i32 1
;
%x = call i32 @llvm.vector.reduce.umin.nxv8i32(<vscale x 8 x i32> splat (i32 1))
ret i32 %x
Expand Down Expand Up @@ -812,8 +800,7 @@ define i32 @umin_poison() {

define i32 @umin_poison_scalable_vector() {
; CHECK-LABEL: @umin_poison_scalable_vector(
; CHECK-NEXT: [[X:%.*]] = call i32 @llvm.vector.reduce.umin.nxv8i32(<vscale x 8 x i32> poison)
; CHECK-NEXT: ret i32 [[X]]
; CHECK-NEXT: ret i32 poison
;
%x = call i32 @llvm.vector.reduce.umin.nxv8i32(<vscale x 8 x i32> poison)
ret i32 %x
Expand All @@ -837,8 +824,7 @@ define i32 @umax_0() {

define i32 @umax_0_scalable_vector() {
; CHECK-LABEL: @umax_0_scalable_vector(
; CHECK-NEXT: [[X:%.*]] = call i32 @llvm.vector.reduce.umax.nxv8i32(<vscale x 8 x i32> zeroinitializer)
; CHECK-NEXT: ret i32 [[X]]
; CHECK-NEXT: ret i32 0
;
%x = call i32 @llvm.vector.reduce.umax.nxv8i32(<vscale x 8 x i32> zeroinitializer)
ret i32 %x
Expand All @@ -854,8 +840,7 @@ define i32 @umax_1() {

define i32 @umax_1_scalable_vector() {
; CHECK-LABEL: @umax_1_scalable_vector(
; CHECK-NEXT: [[X:%.*]] = call i32 @llvm.vector.reduce.umax.nxv8i32(<vscale x 8 x i32> splat (i32 1))
; CHECK-NEXT: ret i32 [[X]]
; CHECK-NEXT: ret i32 1
;
%x = call i32 @llvm.vector.reduce.umax.nxv8i32(<vscale x 8 x i32> splat(i32 1))
ret i32 %x
Expand Down Expand Up @@ -914,8 +899,7 @@ define i32 @umax_poison() {

define i32 @umax_poison_scalable_vector() {
; CHECK-LABEL: @umax_poison_scalable_vector(
; CHECK-NEXT: [[X:%.*]] = call i32 @llvm.vector.reduce.umax.nxv8i32(<vscale x 8 x i32> poison)
; CHECK-NEXT: ret i32 [[X]]
; CHECK-NEXT: ret i32 poison
;
%x = call i32 @llvm.vector.reduce.umax.nxv8i32(<vscale x 8 x i32> poison)
ret i32 %x
Expand Down
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