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[InstCombine] Allow min/max in constant BOp min/max folding #142878

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Jun 6, 2025
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[InstCombine] Allow min/max in constant BOp min/max folding #142878

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db9c88c
pre-commit tests
AlexMaclean Jun 4, 2025
669511a
[InstCombine] Allow min/max in constant BOp min/max folding
AlexMaclean Jun 4, 2025
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47 changes: 33 additions & 14 deletions llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1822,7 +1822,6 @@ static Instruction *foldSelectICmpEq(SelectInst &SI, ICmpInst *ICI,
static Value *foldSelectWithConstOpToBinOp(ICmpInst *Cmp, Value *TrueVal,
Value *FalseVal,
IRBuilderBase &Builder) {
BinaryOperator *BOp;
Constant *C1, *C2, *C3;
Value *X;
CmpPredicate Predicate;
Expand All @@ -1838,30 +1837,48 @@ static Value *foldSelectWithConstOpToBinOp(ICmpInst *Cmp, Value *TrueVal,
Predicate = ICmpInst::getInversePredicate(Predicate);
}

if (!match(TrueVal, m_BinOp(BOp)) || !match(FalseVal, m_Constant(C3)))
if (!match(FalseVal, m_Constant(C3)) || !TrueVal->hasOneUse())
return nullptr;

unsigned Opcode = BOp->getOpcode();
bool IsIntrinsic;
unsigned Opcode;
if (BinaryOperator *BOp = dyn_cast<BinaryOperator>(TrueVal)) {
Opcode = BOp->getOpcode();
IsIntrinsic = false;

// This fold causes some regressions and is primarily intended for
// add and sub. So we early exit for div and rem to minimize the
// regressions.
if (Instruction::isIntDivRem(Opcode))
return nullptr;
// This fold causes some regressions and is primarily intended for
// add and sub. So we early exit for div and rem to minimize the
// regressions.
if (Instruction::isIntDivRem(Opcode))
return nullptr;

if (!match(BOp, m_OneUse(m_BinOp(m_Specific(X), m_Constant(C2)))))
if (!match(BOp, m_BinOp(m_Specific(X), m_Constant(C2))))
return nullptr;

} else if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(TrueVal)) {
if (!match(II, m_MaxOrMin(m_Specific(X), m_Constant(C2))))
return nullptr;
Opcode = II->getIntrinsicID();
IsIntrinsic = true;
} else {
return nullptr;
}

Value *RHS;
SelectPatternFlavor SPF;
const DataLayout &DL = BOp->getDataLayout();
const DataLayout &DL = Cmp->getDataLayout();
auto Flipped = getFlippedStrictnessPredicateAndConstant(Predicate, C1);

if (C3 == ConstantFoldBinaryOpOperands(Opcode, C1, C2, DL)) {
auto FoldBinaryOpOrIntrinsic = [&](Constant *LHS, Constant *RHS) {
return IsIntrinsic ? ConstantFoldBinaryIntrinsic(Opcode, LHS, RHS,
LHS->getType(), nullptr)
: ConstantFoldBinaryOpOperands(Opcode, LHS, RHS, DL);
};

if (C3 == FoldBinaryOpOrIntrinsic(C1, C2)) {
SPF = getSelectPattern(Predicate).Flavor;
RHS = C1;
} else if (Flipped && C3 == ConstantFoldBinaryOpOperands(
Opcode, Flipped->second, C2, DL)) {
} else if (Flipped && C3 == FoldBinaryOpOrIntrinsic(Flipped->second, C2)) {
SPF = getSelectPattern(Flipped->first).Flavor;
RHS = Flipped->second;
} else {
Expand All @@ -1870,7 +1887,9 @@ static Value *foldSelectWithConstOpToBinOp(ICmpInst *Cmp, Value *TrueVal,

Intrinsic::ID IntrinsicID = getMinMaxIntrinsic(SPF);
Value *Intrinsic = Builder.CreateBinaryIntrinsic(IntrinsicID, X, RHS);
return Builder.CreateBinOp(BOp->getOpcode(), Intrinsic, C2);
return IsIntrinsic ? Builder.CreateBinaryIntrinsic(Opcode, Intrinsic, C2)
: Builder.CreateBinOp(Instruction::BinaryOps(Opcode),
Intrinsic, C2);
}

/// Visit a SelectInst that has an ICmpInst as its first operand.
Expand Down
51 changes: 51 additions & 0 deletions llvm/test/Transforms/InstCombine/canonicalize-const-to-bop.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -399,3 +399,54 @@ define i8 @sub_const_on_lhs_negative(i8 %x) {
%s = select i1 %cmp, i8 %sub, i8 50
ret i8 %s
}

define i8 @smin_ugt(i8 %x) {
; CHECK-LABEL: define i8 @smin_ugt(
; CHECK-SAME: i8 [[X:%.*]]) {
; CHECK-NEXT: [[S:%.*]] = call i8 @llvm.umin.i8(i8 [[X]], i8 50)
; CHECK-NEXT: ret i8 [[S]]
;
%smin = call i8 @llvm.smin.i8(i8 %x, i8 50)
%cmp = icmp ugt i8 %x, 100
%s = select i1 %cmp, i8 50, i8 %smin
ret i8 %s
}

define i8 @smax_ugt(i8 %x) {
; CHECK-LABEL: define i8 @smax_ugt(
; CHECK-SAME: i8 [[X:%.*]]) {
; CHECK-NEXT: [[TMP1:%.*]] = call i8 @llvm.umin.i8(i8 [[X]], i8 100)
; CHECK-NEXT: [[S:%.*]] = call i8 @llvm.smax.i8(i8 [[TMP1]], i8 50)
; CHECK-NEXT: ret i8 [[S]]
;
%smax = call i8 @llvm.smax.i8(i8 %x, i8 50)
%cmp = icmp ugt i8 %x, 100
%s = select i1 %cmp, i8 100, i8 %smax
ret i8 %s
}

define i8 @umin_slt(i8 %x) {
; CHECK-LABEL: define i8 @umin_slt(
; CHECK-SAME: i8 [[X:%.*]]) {
; CHECK-NEXT: [[TMP1:%.*]] = call i8 @llvm.smax.i8(i8 [[X]], i8 0)
; CHECK-NEXT: [[S:%.*]] = call i8 @llvm.umin.i8(i8 [[TMP1]], i8 100)
; CHECK-NEXT: ret i8 [[S]]
;
%cmp = icmp slt i8 %x, 0
%umin = tail call i8 @llvm.umin.i8(i8 %x, i8 100)
%s = select i1 %cmp, i8 0, i8 %umin
ret i8 %s
}

define i8 @umax_sgt(i8 %x) {
; CHECK-LABEL: define i8 @umax_sgt(
; CHECK-SAME: i8 [[X:%.*]]) {
; CHECK-NEXT: [[TMP1:%.*]] = call i8 @llvm.smin.i8(i8 [[X]], i8 100)
; CHECK-NEXT: [[S:%.*]] = call i8 @llvm.umax.i8(i8 [[TMP1]], i8 50)
; CHECK-NEXT: ret i8 [[S]]
;
%cmp = icmp sgt i8 %x, 100
%umax = tail call i8 @llvm.umax.i8(i8 %x, i8 50)
%s = select i1 %cmp, i8 100, i8 %umax
ret i8 %s
}
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