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[InstCombine] Canonicalize signed saturated additions #153053

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111 changes: 105 additions & 6 deletions llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
Original file line number Diff line number Diff line change
Expand Up @@ -1012,10 +1012,9 @@ static Value *canonicalizeSaturatedSubtract(const ICmpInst *ICI,
return Result;
}

static Value *canonicalizeSaturatedAdd(ICmpInst *Cmp, Value *TVal, Value *FVal,
InstCombiner::BuilderTy &Builder) {
if (!Cmp->hasOneUse())
return nullptr;
static Value *
canonicalizeSaturatedAddUnsigned(ICmpInst *Cmp, Value *TVal, Value *FVal,
InstCombiner::BuilderTy &Builder) {

// Match unsigned saturated add with constant.
Value *Cmp0 = Cmp->getOperand(0);
Expand All @@ -1037,8 +1036,7 @@ static Value *canonicalizeSaturatedAdd(ICmpInst *Cmp, Value *TVal, Value *FVal,
// uge -1 is canonicalized to eq -1 and requires special handling
// (a == -1) ? -1 : a + 1 -> uadd.sat(a, 1)
if (Pred == ICmpInst::ICMP_EQ) {
if (match(FVal, m_Add(m_Specific(Cmp0), m_One())) &&
match(Cmp1, m_AllOnes())) {
if (match(FVal, m_Add(m_Specific(Cmp0), m_One())) && Cmp1 == TVal) {
return Builder.CreateBinaryIntrinsic(
Intrinsic::uadd_sat, Cmp0, ConstantInt::get(Cmp0->getType(), 1));
}
Expand Down Expand Up @@ -1115,6 +1113,107 @@ static Value *canonicalizeSaturatedAdd(ICmpInst *Cmp, Value *TVal, Value *FVal,
return nullptr;
}

static Value *canonicalizeSaturatedAddSigned(ICmpInst *Cmp, Value *TVal,
Value *FVal,
InstCombiner::BuilderTy &Builder) {
// Match saturated add with constant.
Value *Cmp0 = Cmp->getOperand(0);
Value *Cmp1 = Cmp->getOperand(1);
ICmpInst::Predicate Pred = Cmp->getPredicate();
Value *X, *Y;
const APInt *C;

// Canonicalize INT_MAX to true value of the select.
if (match(FVal, m_MaxSignedValue())) {
std::swap(TVal, FVal);
Pred = CmpInst::getInversePredicate(Pred);
}
if (!match(TVal, m_MaxSignedValue()))
return nullptr;

// sge maximum signed value is canonicalized to eq minimum signed value and
// requires special handling (a == INT_MAX) ? INT_MAX : a + 1 -> sadd.sat(a,
// 1)
if (Pred == ICmpInst::ICMP_EQ) {
if (match(FVal, m_Add(m_Specific(Cmp0), m_One())) && Cmp1 == TVal) {
return Builder.CreateBinaryIntrinsic(
Intrinsic::sadd_sat, Cmp0, ConstantInt::get(Cmp0->getType(), 1));
}
return nullptr;
}

if ((Pred == ICmpInst::ICMP_SGE || Pred == ICmpInst::ICMP_SGT) &&
match(FVal, m_Add(m_Specific(Cmp0), m_APIntAllowPoison(C))) &&
match(Cmp1, m_SpecificIntAllowPoison(
APInt::getSignedMaxValue(
Cmp1->getType()->getScalarSizeInBits()) -
*C)) &&
!C->isNegative()) {
// (X > INT_MAX - C) ? INT_MAX : (X + C) --> sadd.sat(X, C)
// (X >= INT_MAX - C) ? INT_MAX : (X + C) --> sadd.sat(X, C)
return Builder.CreateBinaryIntrinsic(Intrinsic::sadd_sat, Cmp0,
ConstantInt::get(Cmp0->getType(), *C));
}

if (Pred == ICmpInst::ICMP_SGT &&
match(FVal, m_Add(m_Specific(Cmp0), m_APIntAllowPoison(C))) &&
match(Cmp1, m_SpecificIntAllowPoison(
APInt::getSignedMaxValue(
Cmp1->getType()->getScalarSizeInBits()) -
*C - 1)) &&
!C->isNegative()) {
// (X > INT_MAX - C - 1) ? INT_MAX : (X + C) --> sadd.sat(X, C)
return Builder.CreateBinaryIntrinsic(Intrinsic::sadd_sat, Cmp0,
ConstantInt::get(Cmp0->getType(), *C));
}

// This does not work with 0, or negative numbers as
// (X >= INT_MIN + 0 + 1) ? INT_MAX : (X + 0) is not a saturated add.
if (Pred == ICmpInst::ICMP_SGE &&
match(FVal, m_Add(m_Specific(Cmp0), m_APIntAllowPoison(C))) &&
match(Cmp1, m_SpecificIntAllowPoison(
APInt::getSignedMinValue(
Cmp1->getType()->getScalarSizeInBits()) -
*C + 1)) &&
C->isStrictlyPositive()) {
// (X >= INT_MAX - C + 1) ? INT_MAX : (X + C) --> sadd.sat(X, C)
return Builder.CreateBinaryIntrinsic(Intrinsic::sadd_sat, Cmp0,
ConstantInt::get(Cmp0->getType(), *C));
}

// Canonicalize predicate to less-than or less-or-equal-than.
if (Pred == ICmpInst::ICMP_SGT || Pred == ICmpInst::ICMP_SGE) {
std::swap(Cmp0, Cmp1);
Pred = CmpInst::getSwappedPredicate(Pred);
}

if (Pred != ICmpInst::ICMP_SLT && Pred != ICmpInst::ICMP_SLE)
return nullptr;

if (match(Cmp0, m_NSWSub(m_MaxSignedValue(), m_Value(X))) &&
match(FVal, m_c_Add(m_Specific(X), m_Value(Y))) && Y == Cmp1) {
// (INT_MAX - X s< Y) ? INT_MAX : (X + Y) --> sadd.sat(X, Y)
// (INT_MAX - X s< Y) ? INT_MAX : (Y + X) --> sadd.sat(X, Y)
return Builder.CreateBinaryIntrinsic(Intrinsic::sadd_sat, X, Y);
}

return nullptr;
}

static Value *canonicalizeSaturatedAdd(ICmpInst *Cmp, Value *TVal, Value *FVal,
InstCombiner::BuilderTy &Builder) {
if (!Cmp->hasOneUse())
return nullptr;

if (Value *V = canonicalizeSaturatedAddUnsigned(Cmp, TVal, FVal, Builder))
return V;

if (Value *V = canonicalizeSaturatedAddSigned(Cmp, TVal, FVal, Builder))
return V;

return nullptr;
}

/// Try to match patterns with select and subtract as absolute difference.
static Value *foldAbsDiff(ICmpInst *Cmp, Value *TVal, Value *FVal,
InstCombiner::BuilderTy &Builder) {
Expand Down
Original file line number Diff line number Diff line change
Expand Up @@ -123,8 +123,7 @@ define i8 @udiv_slt_exact(i8 %x) {
define i8 @canonicalize_icmp_operands(i8 %x) {
; CHECK-LABEL: define i8 @canonicalize_icmp_operands(
; CHECK-SAME: i8 [[X:%.*]]) {
; CHECK-NEXT: [[TMP1:%.*]] = call i8 @llvm.smin.i8(i8 [[X]], i8 119)
; CHECK-NEXT: [[S:%.*]] = add nsw i8 [[TMP1]], 8
; CHECK-NEXT: [[S:%.*]] = call i8 @llvm.sadd.sat.i8(i8 [[X]], i8 8)
; CHECK-NEXT: ret i8 [[S]]
;
%add = add nsw i8 %x, 8
Expand Down
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