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[InstCombine] Fix a cycle when folding fneg(select) with scalable vector types #112465

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Merged
merged 3 commits into from
Oct 25, 2024
Merged

[InstCombine] Fix a cycle when folding fneg(select) with scalable vector types #112465

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771b154
[InstCombine] Fix a cycle when folding fneg(select) with scalable vec…
ssijaric-nv Oct 16, 2024
e871975
Handle folding of constant splats for scalable vector types
ssijaric-nv Oct 17, 2024
f2e4e8b
Only the constant folding change is needed; revert the fneg folding c…
ssijaric-nv Oct 17, 2024
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29 changes: 15 additions & 14 deletions llvm/lib/IR/ConstantFold.cpp
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Expand Up @@ -581,26 +581,27 @@ Constant *llvm::ConstantFoldUnaryInstruction(unsigned Opcode, Constant *C) {
case Instruction::FNeg:
return ConstantFP::get(C->getContext(), neg(CV));
}
} else if (auto *VTy = dyn_cast<FixedVectorType>(C->getType())) {

Type *Ty = IntegerType::get(VTy->getContext(), 32);
} else if (auto *VTy = dyn_cast<VectorType>(C->getType())) {
// Fast path for splatted constants.
if (Constant *Splat = C->getSplatValue())
if (Constant *Elt = ConstantFoldUnaryInstruction(Opcode, Splat))
return ConstantVector::getSplat(VTy->getElementCount(), Elt);

// Fold each element and create a vector constant from those constants.
SmallVector<Constant *, 16> Result;
for (unsigned i = 0, e = VTy->getNumElements(); i != e; ++i) {
Constant *ExtractIdx = ConstantInt::get(Ty, i);
Constant *Elt = ConstantExpr::getExtractElement(C, ExtractIdx);
Constant *Res = ConstantFoldUnaryInstruction(Opcode, Elt);
if (!Res)
return nullptr;
Result.push_back(Res);
}
if (auto *FVTy = dyn_cast<FixedVectorType>(VTy)) {
// Fold each element and create a vector constant from those constants.
Type *Ty = IntegerType::get(FVTy->getContext(), 32);
SmallVector<Constant *, 16> Result;
for (unsigned i = 0, e = FVTy->getNumElements(); i != e; ++i) {
Constant *ExtractIdx = ConstantInt::get(Ty, i);
Constant *Elt = ConstantExpr::getExtractElement(C, ExtractIdx);
Constant *Res = ConstantFoldUnaryInstruction(Opcode, Elt);
if (!Res)
return nullptr;
Result.push_back(Res);
}

return ConstantVector::get(Result);
return ConstantVector::get(Result);
}
}

// We don't know how to fold this.
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32 changes: 32 additions & 0 deletions llvm/test/Transforms/InstCombine/fneg.ll
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Expand Up @@ -1109,4 +1109,36 @@ define float @test_fneg_select_maxnum(float %x) {
ret float %neg
}

; Check that there's no infinite loop.
define <vscale x 2 x double> @test_fneg_select_svec(<vscale x 2 x i1> %cond, <vscale x 2 x double> %b) {
; CHECK-LABEL: @test_fneg_select_svec(
; CHECK-NEXT: [[TMP2:%.*]] = fneg fast <vscale x 2 x double> [[TMP1:%.*]]
; CHECK-NEXT: [[TMP3:%.*]] = select fast <vscale x 2 x i1> [[COND:%.*]], <vscale x 2 x double> shufflevector (<vscale x 2 x double> insertelement (<vscale x 2 x double> poison, double -0.000000e+00, i64 0), <vscale x 2 x double> poison, <vscale x 2 x i32> zeroinitializer), <vscale x 2 x double> [[TMP2]]
; CHECK-NEXT: ret <vscale x 2 x double> [[TMP3]]
;
%1 = select <vscale x 2 x i1> %cond, <vscale x 2 x double> zeroinitializer, <vscale x 2 x double> %b
%2 = fneg fast <vscale x 2 x double> %1
ret <vscale x 2 x double> %2
}

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Test with zeroinitializer in both positions

define <vscale x 2 x double> @test_fneg_select_svec_2(<vscale x 2 x i1> %cond, <vscale x 2 x double> %a) {
; CHECK-LABEL: @test_fneg_select_svec_2(
; CHECK-NEXT: [[A_NEG:%.*]] = fneg fast <vscale x 2 x double> [[A:%.*]]
; CHECK-NEXT: [[TMP1:%.*]] = select fast <vscale x 2 x i1> [[COND:%.*]], <vscale x 2 x double> [[A_NEG]], <vscale x 2 x double> shufflevector (<vscale x 2 x double> insertelement (<vscale x 2 x double> poison, double -0.000000e+00, i64 0), <vscale x 2 x double> poison, <vscale x 2 x i32> zeroinitializer)
; CHECK-NEXT: ret <vscale x 2 x double> [[TMP1]]
;
%1 = select <vscale x 2 x i1> %cond, <vscale x 2 x double> %a, <vscale x 2 x double> zeroinitializer
%2 = fneg fast <vscale x 2 x double> %1
ret <vscale x 2 x double> %2
}

define <vscale x 2 x double> @test_fneg_select_svec_3(<vscale x 2 x i1> %cond, <vscale x 2 x double> %b) {
; CHECK-LABEL: @test_fneg_select_svec_3(
; CHECK-NEXT: ret <vscale x 2 x double> shufflevector (<vscale x 2 x double> insertelement (<vscale x 2 x double> poison, double -0.000000e+00, i64 0), <vscale x 2 x double> poison, <vscale x 2 x i32> zeroinitializer)
;
%1 = select <vscale x 2 x i1> %cond, <vscale x 2 x double> zeroinitializer, <vscale x 2 x double> zeroinitializer
%2 = fneg fast <vscale x 2 x double> %1
ret <vscale x 2 x double> %2
}

!0 = !{}
6 changes: 2 additions & 4 deletions llvm/test/Transforms/InstSimplify/fp-nan.ll
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Expand Up @@ -237,8 +237,7 @@ define <2 x double> @unary_fneg_nan_2(<2 x double> %x) {
; FIXME: This doesn't behave the same way as the fixed-length vectors above
define <vscale x 1 x double> @unary_fneg_nan_2_scalable_vec_0() {
; CHECK-LABEL: @unary_fneg_nan_2_scalable_vec_0(
; CHECK-NEXT: [[R:%.*]] = fneg <vscale x 1 x double> shufflevector (<vscale x 1 x double> insertelement (<vscale x 1 x double> poison, double 0xFFF1234567890ABC, i64 0), <vscale x 1 x double> poison, <vscale x 1 x i32> zeroinitializer)
; CHECK-NEXT: ret <vscale x 1 x double> [[R]]
; CHECK-NEXT: ret <vscale x 1 x double> shufflevector (<vscale x 1 x double> insertelement (<vscale x 1 x double> poison, double 0x7FF1234567890ABC, i64 0), <vscale x 1 x double> poison, <vscale x 1 x i32> zeroinitializer)
;
%r = fneg <vscale x 1 x double> splat (double 0xFFF1234567890ABC)
ret <vscale x 1 x double> %r
Expand All @@ -247,8 +246,7 @@ define <vscale x 1 x double> @unary_fneg_nan_2_scalable_vec_0() {
; FIXME: This doesn't behave the same way as the fixed-length vectors above
define <vscale x 1 x double> @unary_fneg_nan_2_scalable_vec_1() {
; CHECK-LABEL: @unary_fneg_nan_2_scalable_vec_1(
; CHECK-NEXT: [[R:%.*]] = fneg <vscale x 1 x double> shufflevector (<vscale x 1 x double> insertelement (<vscale x 1 x double> poison, double 0x7FF0000000000001, i64 0), <vscale x 1 x double> poison, <vscale x 1 x i32> zeroinitializer)
; CHECK-NEXT: ret <vscale x 1 x double> [[R]]
; CHECK-NEXT: ret <vscale x 1 x double> shufflevector (<vscale x 1 x double> insertelement (<vscale x 1 x double> poison, double 0xFFF0000000000001, i64 0), <vscale x 1 x double> poison, <vscale x 1 x i32> zeroinitializer)
;
%r = fneg <vscale x 1 x double> splat (double 0x7FF0000000000001)
ret <vscale x 1 x double> %r
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