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[InstCombine] Extend foldSelectInstWithICmpConst to handle minmax #125346

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Feb 2, 2025
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[InstCombine] Extend foldSelectInstWithICmpConst to handle minmax #125346

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c1645ad
[InstCombine] Add pre-commit tests. NFC.
dtcxzyw Feb 1, 2025
926e610
[InstCombine] Extend `foldSelectInstWithICmpConst` to handle minmax
dtcxzyw Feb 1, 2025
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36 changes: 24 additions & 12 deletions llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1771,26 +1771,38 @@ static Value *foldSelectInstWithICmpConst(SelectInst &SI, ICmpInst *ICI,
return Builder.CreateBinaryIntrinsic(Intrinsic::smin, V, TVal);
}

BinaryOperator *BO;
// Fold icmp(X) ? f(X) : C to f(X) when f(X) is guaranteed to be equal to C
// for all X in the exact range of the inverse predicate.
Instruction *Op;
const APInt *C;
CmpInst::Predicate CPred;
if (match(&SI, m_Select(m_Specific(ICI), m_APInt(C), m_BinOp(BO))))
if (match(&SI, m_Select(m_Specific(ICI), m_APInt(C), m_Instruction(Op))))
CPred = ICI->getPredicate();
else if (match(&SI, m_Select(m_Specific(ICI), m_BinOp(BO), m_APInt(C))))
else if (match(&SI, m_Select(m_Specific(ICI), m_Instruction(Op), m_APInt(C))))
CPred = ICI->getInversePredicate();
else
return nullptr;

const APInt *BinOpC;
if (!match(BO, m_BinOp(m_Specific(V), m_APInt(BinOpC))))
return nullptr;

ConstantRange R = ConstantRange::makeExactICmpRegion(CPred, *CmpC)
.binaryOp(BO->getOpcode(), *BinOpC);
if (R == *C) {
BO->dropPoisonGeneratingFlags();
return BO;
ConstantRange InvDomCR = ConstantRange::makeExactICmpRegion(CPred, *CmpC);
const APInt *OpC;
if (match(Op, m_BinOp(m_Specific(V), m_APInt(OpC)))) {
ConstantRange R = InvDomCR.binaryOp(
static_cast<Instruction::BinaryOps>(Op->getOpcode()), *OpC);
if (R == *C) {
Op->dropPoisonGeneratingFlags();
return Op;
}
}
if (auto *MMI = dyn_cast<MinMaxIntrinsic>(Op);
MMI && MMI->getLHS() == V && match(MMI->getRHS(), m_APInt(OpC))) {
ConstantRange R = ConstantRange::intrinsic(MMI->getIntrinsicID(),
{InvDomCR, ConstantRange(*OpC)});
if (R == *C) {
MMI->dropPoisonGeneratingAnnotations();
return MMI;
}
}

return nullptr;
}

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63 changes: 63 additions & 0 deletions llvm/test/Transforms/InstCombine/select-min-max.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -301,3 +301,66 @@ define i8 @not_smin_swap(i8 %i41, i8 %i43) {
%spec.select = select i1 %i44, i8 %i46, i8 0
ret i8 %spec.select
}

define i8 @sel_umin_constant(i8 %x) {
; CHECK-LABEL: @sel_umin_constant(
; CHECK-NEXT: [[UMIN:%.*]] = call i8 @llvm.umin.i8(i8 [[X:%.*]], i8 16)
; CHECK-NEXT: ret i8 [[UMIN]]
;
%cmp = icmp sgt i8 %x, -1
%umin = call i8 @llvm.umin.i8(i8 %x, i8 16)
%sel = select i1 %cmp, i8 %umin, i8 16
ret i8 %sel
}

define i8 @sel_constant_smax_with_range_attr(i8 %x) {
; CHECK-LABEL: @sel_constant_smax_with_range_attr(
; CHECK-NEXT: [[SEL:%.*]] = call i8 @llvm.smax.i8(i8 [[X:%.*]], i8 16)
; CHECK-NEXT: ret i8 [[SEL]]
;
%cmp = icmp slt i8 %x, 0
%smax = call range(i8 8, 16) i8 @llvm.smax.i8(i8 %x, i8 16)
%sel = select i1 %cmp, i8 16, i8 %smax
ret i8 %sel
}

; Negative tests

define i8 @sel_umin_constant_mismatch(i8 %x) {
; CHECK-LABEL: @sel_umin_constant_mismatch(
; CHECK-NEXT: [[CMP:%.*]] = icmp sgt i8 [[X:%.*]], -1
; CHECK-NEXT: [[UMIN:%.*]] = call i8 @llvm.umin.i8(i8 [[X]], i8 16)
; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i8 [[UMIN]], i8 15
; CHECK-NEXT: ret i8 [[SEL]]
;
%cmp = icmp sgt i8 %x, -1
%umin = call i8 @llvm.umin.i8(i8 %x, i8 16)
%sel = select i1 %cmp, i8 %umin, i8 15
ret i8 %sel
}

define i8 @sel_umin_constant_op_mismatch(i8 %x, i8 %y) {
; CHECK-LABEL: @sel_umin_constant_op_mismatch(
; CHECK-NEXT: [[CMP:%.*]] = icmp sgt i8 [[X:%.*]], -1
; CHECK-NEXT: [[UMIN:%.*]] = call i8 @llvm.umin.i8(i8 [[Y:%.*]], i8 16)
; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i8 [[UMIN]], i8 16
; CHECK-NEXT: ret i8 [[SEL]]
;
%cmp = icmp sgt i8 %x, -1
%umin = call i8 @llvm.umin.i8(i8 %y, i8 16)
%sel = select i1 %cmp, i8 %umin, i8 16
ret i8 %sel
}

define i8 @sel_umin_non_constant(i8 %x, i8 %y) {
; CHECK-LABEL: @sel_umin_non_constant(
; CHECK-NEXT: [[UMIN:%.*]] = call i8 @llvm.umin.i8(i8 [[X:%.*]], i8 16)
; CHECK-NEXT: [[CMP1:%.*]] = icmp slt i8 [[X]], 0
; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP1]], i8 [[Y:%.*]], i8 [[UMIN]]
; CHECK-NEXT: ret i8 [[SEL]]
;
%cmp = icmp sgt i8 %x, -1
%umin = call i8 @llvm.umin.i8(i8 %x, i8 16)
%sel = select i1 %cmp, i8 %umin, i8 %y
ret i8 %sel
}