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[InstCombine] Fold select of symmetric selects #99245

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Merged
merged 4 commits into from
Jul 17, 2024
Merged

[InstCombine] Fold select of symmetric selects #99245

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d506897
add tests
tgymnich Jul 14, 2024
a53ff1c
[InstCombine] Add fold for select of symmetric selects
tgymnich Jul 14, 2024
94abd42
update tests
tgymnich Jul 14, 2024
714fad2
simplify DecomposedSelect
tgymnich Jul 17, 2024
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29 changes: 29 additions & 0 deletions llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -3012,6 +3012,32 @@ struct DecomposedSelect {
};
} // namespace

/// Folds patterns like:
/// select c2 (select c1 a b) (select c1 b a)
/// into:
/// select (xor c1 c2) b a
static Instruction *
foldSelectOfSymmetricSelect(SelectInst &OuterSelVal,
InstCombiner::BuilderTy &Builder) {

Value *OuterCond, *InnerCond, *InnerTrueVal, *InnerFalseVal;
if (!match(
&OuterSelVal,
m_Select(m_Value(OuterCond),
m_OneUse(m_Select(m_Value(InnerCond), m_Value(InnerTrueVal),
m_Value(InnerFalseVal))),
m_OneUse(m_Select(m_Deferred(InnerCond),
m_Deferred(InnerFalseVal),
m_Deferred(InnerTrueVal))))))
return nullptr;

if (OuterCond->getType() != InnerCond->getType())
return nullptr;

Value *Xor = Builder.CreateXor(InnerCond, OuterCond);
return SelectInst::Create(Xor, InnerFalseVal, InnerTrueVal);
}

/// Look for patterns like
/// %outer.cond = select i1 %inner.cond, i1 %alt.cond, i1 false
/// %inner.sel = select i1 %inner.cond, i8 %inner.sel.t, i8 %inner.sel.f
Expand Down Expand Up @@ -3987,6 +4013,9 @@ Instruction *InstCombinerImpl::visitSelectInst(SelectInst &SI) {
}
}

if (Instruction *I = foldSelectOfSymmetricSelect(SI, Builder))
return I;

if (Instruction *I = foldNestedSelects(SI, Builder))
return I;

Expand Down
122 changes: 122 additions & 0 deletions llvm/test/Transforms/InstCombine/select-of-symmetric-selects.ll
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Original file line number Diff line number Diff line change
@@ -0,0 +1,122 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt < %s -passes=instcombine -S | FileCheck %s

define i32 @select_of_symmetric_selects(i32 %a, i32 %b, i1 %c1, i1 %c2) {
; CHECK-LABEL: @select_of_symmetric_selects(
; CHECK-NEXT: [[TMP1:%.*]] = xor i1 [[C1:%.*]], [[C2:%.*]]
; CHECK-NEXT: [[RET:%.*]] = select i1 [[TMP1]], i32 [[B:%.*]], i32 [[A:%.*]]
; CHECK-NEXT: ret i32 [[RET]]
;
%sel1 = select i1 %c1, i32 %a, i32 %b
%sel2 = select i1 %c1, i32 %b, i32 %a
%ret = select i1 %c2, i32 %sel1, i32 %sel2
ret i32 %ret
}

define i32 @select_of_symmetric_selects_negative1(i32 %a, i32 %b, i1 %c1, i1 %c2) {
; CHECK-LABEL: @select_of_symmetric_selects_negative1(
; CHECK-NEXT: [[SEL1:%.*]] = select i1 [[C1:%.*]], i32 [[A:%.*]], i32 [[B:%.*]]
; CHECK-NEXT: [[RET:%.*]] = select i1 [[C2:%.*]], i32 [[SEL1]], i32 [[A]]
; CHECK-NEXT: ret i32 [[RET]]
;
%sel1 = select i1 %c1, i32 %a, i32 %b
%sel2 = select i1 %c2, i32 %b, i32 %a
%ret = select i1 %c2, i32 %sel1, i32 %sel2
ret i32 %ret
}

define i32 @select_of_symmetric_selects_negative2(i32 %a, i32 %b, i32 %c, i1 %c1, i1 %c2) {
; CHECK-LABEL: @select_of_symmetric_selects_negative2(
; CHECK-NEXT: [[SEL1:%.*]] = select i1 [[C1:%.*]], i32 [[A:%.*]], i32 [[B:%.*]]
; CHECK-NEXT: [[SEL2:%.*]] = select i1 [[C1]], i32 [[B]], i32 [[C:%.*]]
; CHECK-NEXT: [[RET:%.*]] = select i1 [[C2:%.*]], i32 [[SEL1]], i32 [[SEL2]]
; CHECK-NEXT: ret i32 [[RET]]
;
%sel1 = select i1 %c1, i32 %a, i32 %b
%sel2 = select i1 %c1, i32 %b, i32 %c
%ret = select i1 %c2, i32 %sel1, i32 %sel2
ret i32 %ret
}

declare void @use(i32)

define i32 @select_of_symmetric_selects_multi_use1(i32 %a, i32 %b, i1 %c1, i1 %c2) {
; CHECK-LABEL: @select_of_symmetric_selects_multi_use1(
; CHECK-NEXT: [[SEL1:%.*]] = select i1 [[C1:%.*]], i32 [[A:%.*]], i32 [[B:%.*]]
; CHECK-NEXT: [[SEL2:%.*]] = select i1 [[C1]], i32 [[B]], i32 [[A]]
; CHECK-NEXT: call void @use(i32 [[SEL2]])
; CHECK-NEXT: [[RET:%.*]] = select i1 [[C2:%.*]], i32 [[SEL1]], i32 [[SEL2]]
; CHECK-NEXT: ret i32 [[RET]]
;
%sel1 = select i1 %c1, i32 %a, i32 %b
%sel2 = select i1 %c1, i32 %b, i32 %a
call void @use(i32 %sel2)
%ret = select i1 %c2, i32 %sel1, i32 %sel2
ret i32 %ret
}

define i32 @select_of_symmetric_selects_multi_use2(i32 %a, i32 %b, i1 %c1, i1 %c2) {
; CHECK-LABEL: @select_of_symmetric_selects_multi_use2(
; CHECK-NEXT: [[SEL1:%.*]] = select i1 [[C1:%.*]], i32 [[A:%.*]], i32 [[B:%.*]]
; CHECK-NEXT: call void @use(i32 [[SEL1]])
; CHECK-NEXT: [[SEL2:%.*]] = select i1 [[C1]], i32 [[B]], i32 [[A]]
; CHECK-NEXT: call void @use(i32 [[SEL2]])
; CHECK-NEXT: [[RET:%.*]] = select i1 [[C2:%.*]], i32 [[SEL1]], i32 [[SEL2]]
; CHECK-NEXT: ret i32 [[RET]]
;
%sel1 = select i1 %c1, i32 %a, i32 %b
call void @use(i32 %sel1)
%sel2 = select i1 %c1, i32 %b, i32 %a
call void @use(i32 %sel2)
%ret = select i1 %c2, i32 %sel1, i32 %sel2
ret i32 %ret
}

define i32 @select_of_symmetric_selects_commuted(i32 %a, i32 %b, i1 %c1, i1 %c2) {
; CHECK-LABEL: @select_of_symmetric_selects_commuted(
; CHECK-NEXT: [[TMP1:%.*]] = xor i1 [[C1:%.*]], [[C2:%.*]]
; CHECK-NEXT: [[RET:%.*]] = select i1 [[TMP1]], i32 [[A:%.*]], i32 [[B:%.*]]
; CHECK-NEXT: ret i32 [[RET]]
;
%sel1 = select i1 %c1, i32 %a, i32 %b
%sel2 = select i1 %c1, i32 %b, i32 %a
%ret = select i1 %c2, i32 %sel2, i32 %sel1
ret i32 %ret
}

define <4 x i32> @select_of_symmetric_selects_vector1(<4 x i32> %a, <4 x i32> %b, i1 %c1, i1 %c2) {
; CHECK-LABEL: @select_of_symmetric_selects_vector1(
; CHECK-NEXT: [[TMP1:%.*]] = xor i1 [[C1:%.*]], [[C2:%.*]]
; CHECK-NEXT: [[RET:%.*]] = select i1 [[TMP1]], <4 x i32> [[A:%.*]], <4 x i32> [[B:%.*]]
; CHECK-NEXT: ret <4 x i32> [[RET]]
;
%sel1 = select i1 %c1, <4 x i32> %a, <4 x i32> %b
%sel2 = select i1 %c1, <4 x i32> %b, <4 x i32> %a
%ret = select i1 %c2, <4 x i32> %sel2, <4 x i32> %sel1
ret <4 x i32> %ret
}

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) {
; CHECK-LABEL: @select_of_symmetric_selects_vector2(
; CHECK-NEXT: [[TMP1:%.*]] = xor <4 x i1> [[C1:%.*]], [[C2:%.*]]
; CHECK-NEXT: [[RET:%.*]] = select <4 x i1> [[TMP1]], <4 x i32> [[A:%.*]], <4 x i32> [[B:%.*]]
; CHECK-NEXT: ret <4 x i32> [[RET]]
;
%sel1 = select <4 x i1> %c1, <4 x i32> %a, <4 x i32> %b
%sel2 = select <4 x i1> %c1, <4 x i32> %b, <4 x i32> %a
%ret = select <4 x i1> %c2, <4 x i32> %sel2, <4 x i32> %sel1
ret <4 x i32> %ret
}

define <2 x i32> @select_of_symmetric_selects_vector3(<2 x i32> %a, <2 x i32> %b, <2 x i1> %c1, i1 %c2) {
; CHECK-LABEL: @select_of_symmetric_selects_vector3(
; CHECK-NEXT: [[SEL1:%.*]] = select <2 x i1> [[C1:%.*]], <2 x i32> [[A:%.*]], <2 x i32> [[B:%.*]]
; CHECK-NEXT: [[SEL2:%.*]] = select <2 x i1> [[C1]], <2 x i32> [[B]], <2 x i32> [[A]]
; CHECK-NEXT: [[RET:%.*]] = select i1 [[C2:%.*]], <2 x i32> [[SEL1]], <2 x i32> [[SEL2]]
; CHECK-NEXT: ret <2 x i32> [[RET]]
;
%sel1 = select <2 x i1> %c1, <2 x i32> %a, <2 x i32> %b
%sel2 = select <2 x i1> %c1, <2 x i32> %b, <2 x i32> %a
%ret = select i1 %c2, <2 x i32> %sel1, <2 x i32> %sel2
ret <2 x i32> %ret
}
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