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tgymnichtgymnich
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[InstCombine] Fold select of symmetric selects (#99245)
fixes #98800 Fold patterns like: select c2 (select c1 a b) (select c1 b a) into: select (xor c1 c2) b a Alive2 proofs: https://alive2.llvm.org/ce/z/4QAm4K https://alive2.llvm.org/ce/z/vTVRnC
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‎llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp

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Original file line numberDiff line numberDiff line change
@@ -3012,6 +3012,32 @@ struct DecomposedSelect {
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};
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} // namespace
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/// Folds patterns like:
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/// select c2 (select c1 a b) (select c1 b a)
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/// into:
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/// select (xor c1 c2) b a
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static Instruction *
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foldSelectOfSymmetricSelect(SelectInst &OuterSelVal,
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InstCombiner::BuilderTy &Builder) {
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Value *OuterCond, *InnerCond, *InnerTrueVal, *InnerFalseVal;
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if (!match(
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&OuterSelVal,
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m_Select(m_Value(OuterCond),
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m_OneUse(m_Select(m_Value(InnerCond), m_Value(InnerTrueVal),
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m_Value(InnerFalseVal))),
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m_OneUse(m_Select(m_Deferred(InnerCond),
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m_Deferred(InnerFalseVal),
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m_Deferred(InnerTrueVal))))))
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return nullptr;
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if (OuterCond->getType() != InnerCond->getType())
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return nullptr;
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Value *Xor = Builder.CreateXor(InnerCond, OuterCond);
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return SelectInst::Create(Xor, InnerFalseVal, InnerTrueVal);
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}
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/// Look for patterns like
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/// %outer.cond = select i1 %inner.cond, i1 %alt.cond, i1 false
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/// %inner.sel = select i1 %inner.cond, i8 %inner.sel.t, i8 %inner.sel.f
@@ -3987,6 +4013,9 @@ Instruction *InstCombinerImpl::visitSelectInst(SelectInst &SI) {
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}
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}
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if (Instruction *I = foldSelectOfSymmetricSelect(SI, Builder))
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return I;
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if (Instruction *I = foldNestedSelects(SI, Builder))
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return I;
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‎llvm/test/Transforms/InstCombine/select-of-symmetric-selects.ll

Lines changed: 122 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,122 @@
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; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
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; RUN: opt < %s -passes=instcombine -S | FileCheck %s
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define i32 @select_of_symmetric_selects(i32 %a, i32 %b, i1 %c1, i1 %c2) {
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; CHECK-LABEL: @select_of_symmetric_selects(
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; CHECK-NEXT: [[TMP1:%.*]] = xor i1 [[C1:%.*]], [[C2:%.*]]
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; CHECK-NEXT: [[RET:%.*]] = select i1 [[TMP1]], i32 [[B:%.*]], i32 [[A:%.*]]
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; CHECK-NEXT: ret i32 [[RET]]
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;
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%sel1 = select i1 %c1, i32 %a, i32 %b
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%sel2 = select i1 %c1, i32 %b, i32 %a
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%ret = select i1 %c2, i32 %sel1, i32 %sel2
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ret i32 %ret
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}
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define i32 @select_of_symmetric_selects_negative1(i32 %a, i32 %b, i1 %c1, i1 %c2) {
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; CHECK-LABEL: @select_of_symmetric_selects_negative1(
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; CHECK-NEXT: [[SEL1:%.*]] = select i1 [[C1:%.*]], i32 [[A:%.*]], i32 [[B:%.*]]
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; CHECK-NEXT: [[RET:%.*]] = select i1 [[C2:%.*]], i32 [[SEL1]], i32 [[A]]
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; CHECK-NEXT: ret i32 [[RET]]
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;
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%sel1 = select i1 %c1, i32 %a, i32 %b
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%sel2 = select i1 %c2, i32 %b, i32 %a
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%ret = select i1 %c2, i32 %sel1, i32 %sel2
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ret i32 %ret
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}
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define i32 @select_of_symmetric_selects_negative2(i32 %a, i32 %b, i32 %c, i1 %c1, i1 %c2) {
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; CHECK-LABEL: @select_of_symmetric_selects_negative2(
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; CHECK-NEXT: [[SEL1:%.*]] = select i1 [[C1:%.*]], i32 [[A:%.*]], i32 [[B:%.*]]
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; CHECK-NEXT: [[SEL2:%.*]] = select i1 [[C1]], i32 [[B]], i32 [[C:%.*]]
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; CHECK-NEXT: [[RET:%.*]] = select i1 [[C2:%.*]], i32 [[SEL1]], i32 [[SEL2]]
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; CHECK-NEXT: ret i32 [[RET]]
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;
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%sel1 = select i1 %c1, i32 %a, i32 %b
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%sel2 = select i1 %c1, i32 %b, i32 %c
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%ret = select i1 %c2, i32 %sel1, i32 %sel2
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ret i32 %ret
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}
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declare void @use(i32)
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define i32 @select_of_symmetric_selects_multi_use1(i32 %a, i32 %b, i1 %c1, i1 %c2) {
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; CHECK-LABEL: @select_of_symmetric_selects_multi_use1(
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; CHECK-NEXT: [[SEL1:%.*]] = select i1 [[C1:%.*]], i32 [[A:%.*]], i32 [[B:%.*]]
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; CHECK-NEXT: [[SEL2:%.*]] = select i1 [[C1]], i32 [[B]], i32 [[A]]
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; CHECK-NEXT: call void @use(i32 [[SEL2]])
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; CHECK-NEXT: [[RET:%.*]] = select i1 [[C2:%.*]], i32 [[SEL1]], i32 [[SEL2]]
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; CHECK-NEXT: ret i32 [[RET]]
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;
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%sel1 = select i1 %c1, i32 %a, i32 %b
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%sel2 = select i1 %c1, i32 %b, i32 %a
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call void @use(i32 %sel2)
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%ret = select i1 %c2, i32 %sel1, i32 %sel2
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ret i32 %ret
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}
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define i32 @select_of_symmetric_selects_multi_use2(i32 %a, i32 %b, i1 %c1, i1 %c2) {
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; CHECK-LABEL: @select_of_symmetric_selects_multi_use2(
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; CHECK-NEXT: [[SEL1:%.*]] = select i1 [[C1:%.*]], i32 [[A:%.*]], i32 [[B:%.*]]
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; CHECK-NEXT: call void @use(i32 [[SEL1]])
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; CHECK-NEXT: [[SEL2:%.*]] = select i1 [[C1]], i32 [[B]], i32 [[A]]
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; CHECK-NEXT: call void @use(i32 [[SEL2]])
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; CHECK-NEXT: [[RET:%.*]] = select i1 [[C2:%.*]], i32 [[SEL1]], i32 [[SEL2]]
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; CHECK-NEXT: ret i32 [[RET]]
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;
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%sel1 = select i1 %c1, i32 %a, i32 %b
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call void @use(i32 %sel1)
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%sel2 = select i1 %c1, i32 %b, i32 %a
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call void @use(i32 %sel2)
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%ret = select i1 %c2, i32 %sel1, i32 %sel2
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ret i32 %ret
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}
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define i32 @select_of_symmetric_selects_commuted(i32 %a, i32 %b, i1 %c1, i1 %c2) {
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; CHECK-LABEL: @select_of_symmetric_selects_commuted(
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; CHECK-NEXT: [[TMP1:%.*]] = xor i1 [[C1:%.*]], [[C2:%.*]]
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; CHECK-NEXT: [[RET:%.*]] = select i1 [[TMP1]], i32 [[A:%.*]], i32 [[B:%.*]]
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; CHECK-NEXT: ret i32 [[RET]]
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;
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%sel1 = select i1 %c1, i32 %a, i32 %b
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%sel2 = select i1 %c1, i32 %b, i32 %a
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%ret = select i1 %c2, i32 %sel2, i32 %sel1
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ret i32 %ret
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}
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define <4 x i32> @select_of_symmetric_selects_vector1(<4 x i32> %a, <4 x i32> %b, i1 %c1, i1 %c2) {
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; CHECK-LABEL: @select_of_symmetric_selects_vector1(
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; CHECK-NEXT: [[TMP1:%.*]] = xor i1 [[C1:%.*]], [[C2:%.*]]
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; CHECK-NEXT: [[RET:%.*]] = select i1 [[TMP1]], <4 x i32> [[A:%.*]], <4 x i32> [[B:%.*]]
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; CHECK-NEXT: ret <4 x i32> [[RET]]
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;
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%sel1 = select i1 %c1, <4 x i32> %a, <4 x i32> %b
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%sel2 = select i1 %c1, <4 x i32> %b, <4 x i32> %a
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%ret = select i1 %c2, <4 x i32> %sel2, <4 x i32> %sel1
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ret <4 x i32> %ret
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}
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define <4 x i32> @select_of_symmetric_selects_vector2(<4 x i32> %a, <4 x i32> %b, <4 x i1> %c1, <4 x i1> %c2) {
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; CHECK-LABEL: @select_of_symmetric_selects_vector2(
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; CHECK-NEXT: [[TMP1:%.*]] = xor <4 x i1> [[C1:%.*]], [[C2:%.*]]
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; CHECK-NEXT: [[RET:%.*]] = select <4 x i1> [[TMP1]], <4 x i32> [[A:%.*]], <4 x i32> [[B:%.*]]
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; CHECK-NEXT: ret <4 x i32> [[RET]]
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;
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%sel1 = select <4 x i1> %c1, <4 x i32> %a, <4 x i32> %b
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%sel2 = select <4 x i1> %c1, <4 x i32> %b, <4 x i32> %a
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%ret = select <4 x i1> %c2, <4 x i32> %sel2, <4 x i32> %sel1
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ret <4 x i32> %ret
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}
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define <2 x i32> @select_of_symmetric_selects_vector3(<2 x i32> %a, <2 x i32> %b, <2 x i1> %c1, i1 %c2) {
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; CHECK-LABEL: @select_of_symmetric_selects_vector3(
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; CHECK-NEXT: [[SEL1:%.*]] = select <2 x i1> [[C1:%.*]], <2 x i32> [[A:%.*]], <2 x i32> [[B:%.*]]
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; CHECK-NEXT: [[SEL2:%.*]] = select <2 x i1> [[C1]], <2 x i32> [[B]], <2 x i32> [[A]]
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; CHECK-NEXT: [[RET:%.*]] = select i1 [[C2:%.*]], <2 x i32> [[SEL1]], <2 x i32> [[SEL2]]
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; CHECK-NEXT: ret <2 x i32> [[RET]]
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;
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%sel1 = select <2 x i1> %c1, <2 x i32> %a, <2 x i32> %b
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%sel2 = select <2 x i1> %c1, <2 x i32> %b, <2 x i32> %a
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%ret = select i1 %c2, <2 x i32> %sel1, <2 x i32> %sel2
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ret <2 x i32> %ret
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}

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