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DAGCombiner: Continue combining if FoldConstantArithmetic() fails.
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DAG.FoldConstantArithmetic() can fail even though both operands are
Constants if OpaqueConstants are involved. Continue trying other combine
possibilities in tis case.

Differential Revision: http://reviews.llvm.org/D6946

Somewhat related to PR21801 / rdar://19211454

llvm-svn: 237822
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@MatzeB
MatzeB committed May 20, 2015
1 parent 2b21a7c commit 56a7814
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Showing 2 changed files with 106 additions and 74 deletions.
168 changes: 95 additions & 73 deletions llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1595,6 +1595,13 @@ static bool isOneConstant(SDValue V) {
return Const != nullptr && Const->isOne();
}

/// If \p N is a ContantSDNode with isOpaque() == false return it casted to a
/// ContantSDNode pointer else nullptr.
static ConstantSDNode *getAsNonOpaqueConstant(SDValue N) {
ConstantSDNode *Const = dyn_cast<ConstantSDNode>(N);
return Const != nullptr && !Const->isOpaque() ? Const : nullptr;
}

SDValue DAGCombiner::visitADD(SDNode *N) {
SDValue N0 = N->getOperand(0);
SDValue N1 = N->getOperand(1);
Expand All @@ -1618,8 +1625,8 @@ SDValue DAGCombiner::visitADD(SDNode *N) {
if (N1.getOpcode() == ISD::UNDEF)
return N1;
// fold (add c1, c2) -> c1+c2
ConstantSDNode *N0C = dyn_cast<ConstantSDNode>(N0);
ConstantSDNode *N1C = dyn_cast<ConstantSDNode>(N1);
ConstantSDNode *N0C = getAsNonOpaqueConstant(N0);
ConstantSDNode *N1C = getAsNonOpaqueConstant(N1);
if (N0C && N1C)
return DAG.FoldConstantArithmetic(ISD::ADD, SDLoc(N), VT, N0C, N1C);
// canonicalize constant to RHS
Expand All @@ -1638,7 +1645,7 @@ SDValue DAGCombiner::visitADD(SDNode *N) {
(uint64_t)N1C->getSExtValue());
// fold ((c1-A)+c2) -> (c1+c2)-A
if (N1C && N0.getOpcode() == ISD::SUB)
if (ConstantSDNode *N0C = dyn_cast<ConstantSDNode>(N0.getOperand(0))) {
if (ConstantSDNode *N0C = getAsNonOpaqueConstant(N0.getOperand(0))) {
SDLoc DL(N);
return DAG.getNode(ISD::SUB, DL, VT,
DAG.getConstant(N1C->getAPIntValue()+
Expand Down Expand Up @@ -1853,8 +1860,8 @@ SDValue DAGCombiner::visitSUB(SDNode *N) {
if (N0 == N1)
return tryFoldToZero(SDLoc(N), TLI, VT, DAG, LegalOperations, LegalTypes);
// fold (sub c1, c2) -> c1-c2
ConstantSDNode *N0C = dyn_cast<ConstantSDNode>(N0.getNode());
ConstantSDNode *N1C = dyn_cast<ConstantSDNode>(N1.getNode());
ConstantSDNode *N0C = getAsNonOpaqueConstant(N0);
ConstantSDNode *N1C = getAsNonOpaqueConstant(N1);
if (N0C && N1C)
return DAG.FoldConstantArithmetic(ISD::SUB, SDLoc(N), VT, N0C, N1C);
// fold (sub x, c) -> (add x, -c)
Expand Down Expand Up @@ -1996,6 +2003,8 @@ SDValue DAGCombiner::visitMUL(SDNode *N) {

bool N0IsConst = false;
bool N1IsConst = false;
bool N1IsOpaqueConst = false;
bool N0IsOpaqueConst = false;
APInt ConstValue0, ConstValue1;
// fold vector ops
if (VT.isVector()) {
Expand All @@ -2006,15 +2015,19 @@ SDValue DAGCombiner::visitMUL(SDNode *N) {
N1IsConst = isConstantSplatVector(N1.getNode(), ConstValue1);
} else {
N0IsConst = isa<ConstantSDNode>(N0);
if (N0IsConst)
if (N0IsConst) {
ConstValue0 = cast<ConstantSDNode>(N0)->getAPIntValue();
N0IsOpaqueConst = cast<ConstantSDNode>(N0)->isOpaque();
}
N1IsConst = isa<ConstantSDNode>(N1);
if (N1IsConst)
if (N1IsConst) {
ConstValue1 = cast<ConstantSDNode>(N1)->getAPIntValue();
N1IsOpaqueConst = cast<ConstantSDNode>(N1)->isOpaque();
}
}

// fold (mul c1, c2) -> c1*c2
if (N0IsConst && N1IsConst)
if (N0IsConst && N1IsConst && !N0IsOpaqueConst && !N1IsOpaqueConst)
return DAG.FoldConstantArithmetic(ISD::MUL, SDLoc(N), VT,
N0.getNode(), N1.getNode());

Expand All @@ -2039,14 +2052,16 @@ SDValue DAGCombiner::visitMUL(SDNode *N) {
DAG.getConstant(0, DL, VT), N0);
}
// fold (mul x, (1 << c)) -> x << c
if (N1IsConst && ConstValue1.isPowerOf2() && IsFullSplat) {
if (N1IsConst && !N1IsOpaqueConst && ConstValue1.isPowerOf2() &&
IsFullSplat) {
SDLoc DL(N);
return DAG.getNode(ISD::SHL, DL, VT, N0,
DAG.getConstant(ConstValue1.logBase2(), DL,
getShiftAmountTy(N0.getValueType())));
}
// fold (mul x, -(1 << c)) -> -(x << c) or (-x) << c
if (N1IsConst && (-ConstValue1).isPowerOf2() && IsFullSplat) {
if (N1IsConst && !N1IsOpaqueConst && (-ConstValue1).isPowerOf2() &&
IsFullSplat) {
unsigned Log2Val = (-ConstValue1).logBase2();
SDLoc DL(N);
// FIXME: If the input is something that is easily negated (e.g. a
Expand Down Expand Up @@ -2124,7 +2139,7 @@ SDValue DAGCombiner::visitSDIV(SDNode *N) {
// fold (sdiv c1, c2) -> c1/c2
ConstantSDNode *N0C = isConstOrConstSplat(N0);
ConstantSDNode *N1C = isConstOrConstSplat(N1);
if (N0C && N1C && !N1C->isNullValue())
if (N0C && N1C && !N0C->isOpaque() && !N1C->isOpaque())
return DAG.FoldConstantArithmetic(ISD::SDIV, SDLoc(N), VT, N0C, N1C);
// fold (sdiv X, 1) -> X
if (N1C && N1C->isOne())
Expand All @@ -2144,8 +2159,9 @@ SDValue DAGCombiner::visitSDIV(SDNode *N) {
}

// fold (sdiv X, pow2) -> simple ops after legalize
if (N1C && !N1C->isNullValue() && (N1C->getAPIntValue().isPowerOf2() ||
(-N1C->getAPIntValue()).isPowerOf2())) {
if (N1C && !N1C->isNullValue() && !N1C->isOpaque() &&
(N1C->getAPIntValue().isPowerOf2() ||
(-N1C->getAPIntValue()).isPowerOf2())) {
// If dividing by powers of two is cheap, then don't perform the following
// fold.
if (TLI.isPow2SDivCheap())
Expand Down Expand Up @@ -2217,18 +2233,20 @@ SDValue DAGCombiner::visitUDIV(SDNode *N) {
// fold (udiv c1, c2) -> c1/c2
ConstantSDNode *N0C = isConstOrConstSplat(N0);
ConstantSDNode *N1C = isConstOrConstSplat(N1);
if (N0C && N1C && !N1C->isNullValue())
return DAG.FoldConstantArithmetic(ISD::UDIV, SDLoc(N), VT, N0C, N1C);
if (N0C && N1C)
if (SDValue Folded = DAG.FoldConstantArithmetic(ISD::UDIV, SDLoc(N), VT,
N0C, N1C))
return Folded;
// fold (udiv x, (1 << c)) -> x >>u c
if (N1C && N1C->getAPIntValue().isPowerOf2()) {
if (N1C && !N1C->isOpaque() && N1C->getAPIntValue().isPowerOf2()) {
SDLoc DL(N);
return DAG.getNode(ISD::SRL, DL, VT, N0,
DAG.getConstant(N1C->getAPIntValue().logBase2(), DL,
getShiftAmountTy(N0.getValueType())));
}
// fold (udiv x, (shl c, y)) -> x >>u (log2(c)+y) iff c is power of 2
if (N1.getOpcode() == ISD::SHL) {
if (ConstantSDNode *SHC = dyn_cast<ConstantSDNode>(N1.getOperand(0))) {
if (ConstantSDNode *SHC = getAsNonOpaqueConstant(N1.getOperand(0))) {
if (SHC->getAPIntValue().isPowerOf2()) {
EVT ADDVT = N1.getOperand(1).getValueType();
SDLoc DL(N);
Expand Down Expand Up @@ -2266,8 +2284,10 @@ SDValue DAGCombiner::visitSREM(SDNode *N) {
// fold (srem c1, c2) -> c1%c2
ConstantSDNode *N0C = isConstOrConstSplat(N0);
ConstantSDNode *N1C = isConstOrConstSplat(N1);
if (N0C && N1C && !N1C->isNullValue())
return DAG.FoldConstantArithmetic(ISD::SREM, SDLoc(N), VT, N0C, N1C);
if (N0C && N1C)
if (SDValue Folded = DAG.FoldConstantArithmetic(ISD::SREM, SDLoc(N), VT,
N0C, N1C))
return Folded;
// If we know the sign bits of both operands are zero, strength reduce to a
// urem instead. Handles (X & 0x0FFFFFFF) %s 16 -> X&15
if (!VT.isVector()) {
Expand Down Expand Up @@ -2308,17 +2328,20 @@ SDValue DAGCombiner::visitUREM(SDNode *N) {
// fold (urem c1, c2) -> c1%c2
ConstantSDNode *N0C = isConstOrConstSplat(N0);
ConstantSDNode *N1C = isConstOrConstSplat(N1);
if (N0C && N1C && !N1C->isNullValue())
return DAG.FoldConstantArithmetic(ISD::UREM, SDLoc(N), VT, N0C, N1C);
if (N0C && N1C)
if (SDValue Folded = DAG.FoldConstantArithmetic(ISD::UREM, SDLoc(N), VT,
N0C, N1C))
return Folded;
// fold (urem x, pow2) -> (and x, pow2-1)
if (N1C && !N1C->isNullValue() && N1C->getAPIntValue().isPowerOf2()) {
if (N1C && !N1C->isNullValue() && !N1C->isOpaque() &&
N1C->getAPIntValue().isPowerOf2()) {
SDLoc DL(N);
return DAG.getNode(ISD::AND, DL, VT, N0,
DAG.getConstant(N1C->getAPIntValue() - 1, DL, VT));
}
// fold (urem x, (shl pow2, y)) -> (and x, (add (shl pow2, y), -1))
if (N1.getOpcode() == ISD::SHL) {
if (ConstantSDNode *SHC = dyn_cast<ConstantSDNode>(N1.getOperand(0))) {
if (ConstantSDNode *SHC = getAsNonOpaqueConstant(N1.getOperand(0))) {
if (SHC->getAPIntValue().isPowerOf2()) {
SDLoc DL(N);
SDValue Add =
Expand Down Expand Up @@ -2872,9 +2895,9 @@ SDValue DAGCombiner::visitAND(SDNode *N) {
}

// fold (and c1, c2) -> c1&c2
ConstantSDNode *N0C = dyn_cast<ConstantSDNode>(N0);
ConstantSDNode *N0C = getAsNonOpaqueConstant(N0);
ConstantSDNode *N1C = dyn_cast<ConstantSDNode>(N1);
if (N0C && N1C)
if (N0C && N1C && !N1C->isOpaque())
return DAG.FoldConstantArithmetic(ISD::AND, SDLoc(N), VT, N0C, N1C);
// canonicalize constant to RHS
if (isConstantIntBuildVectorOrConstantInt(N0) &&
Expand Down Expand Up @@ -3468,26 +3491,29 @@ SDValue DAGCombiner::visitORLike(SDValue N0, SDValue N1, SDNode *LocReference) {
}

// (or (and X, C1), (and Y, C2)) -> (and (or X, Y), C3) if possible.
if (N0.getOpcode() == ISD::AND &&
N1.getOpcode() == ISD::AND &&
N0.getOperand(1).getOpcode() == ISD::Constant &&
N1.getOperand(1).getOpcode() == ISD::Constant &&
if (N0.getOpcode() == ISD::AND && N1.getOpcode() == ISD::AND &&
// Don't increase # computations.
(N0.getNode()->hasOneUse() || N1.getNode()->hasOneUse())) {
// We can only do this xform if we know that bits from X that are set in C2
// but not in C1 are already zero. Likewise for Y.
const APInt &LHSMask =
cast<ConstantSDNode>(N0.getOperand(1))->getAPIntValue();
const APInt &RHSMask =
cast<ConstantSDNode>(N1.getOperand(1))->getAPIntValue();

if (DAG.MaskedValueIsZero(N0.getOperand(0), RHSMask&~LHSMask) &&
DAG.MaskedValueIsZero(N1.getOperand(0), LHSMask&~RHSMask)) {
SDValue X = DAG.getNode(ISD::OR, SDLoc(N0), VT,
N0.getOperand(0), N1.getOperand(0));
SDLoc DL(LocReference);
return DAG.getNode(ISD::AND, DL, VT, X,
DAG.getConstant(LHSMask | RHSMask, DL, VT));
if (const ConstantSDNode *N0O1C =
getAsNonOpaqueConstant(N0.getOperand(1))) {
if (const ConstantSDNode *N1O1C =
getAsNonOpaqueConstant(N1.getOperand(1))) {
// We can only do this xform if we know that bits from X that are set in
// C2 but not in C1 are already zero. Likewise for Y.
const APInt &LHSMask = N0O1C->getAPIntValue();
const APInt &RHSMask = N1O1C->getAPIntValue();

if (DAG.MaskedValueIsZero(N0.getOperand(0), RHSMask&~LHSMask) &&
DAG.MaskedValueIsZero(N1.getOperand(0), LHSMask&~RHSMask)) {
SDValue X = DAG.getNode(ISD::OR, SDLoc(N0), VT,
N0.getOperand(0), N1.getOperand(0));
SDLoc DL(LocReference);
return DAG.getNode(ISD::AND, DL, VT, X,
DAG.getConstant(LHSMask | RHSMask, DL, VT));
}
}
}
}

Expand Down Expand Up @@ -3593,9 +3619,9 @@ SDValue DAGCombiner::visitOR(SDNode *N) {
}

// fold (or c1, c2) -> c1|c2
ConstantSDNode *N0C = dyn_cast<ConstantSDNode>(N0);
ConstantSDNode *N0C = getAsNonOpaqueConstant(N0);
ConstantSDNode *N1C = dyn_cast<ConstantSDNode>(N1);
if (N0C && N1C)
if (N0C && N1C && !N1C->isOpaque())
return DAG.FoldConstantArithmetic(ISD::OR, SDLoc(N), VT, N0C, N1C);
// canonicalize constant to RHS
if (isConstantIntBuildVectorOrConstantInt(N0) &&
Expand Down Expand Up @@ -3937,8 +3963,8 @@ SDValue DAGCombiner::visitXOR(SDNode *N) {
if (N1.getOpcode() == ISD::UNDEF)
return N1;
// fold (xor c1, c2) -> c1^c2
ConstantSDNode *N0C = dyn_cast<ConstantSDNode>(N0);
ConstantSDNode *N1C = dyn_cast<ConstantSDNode>(N1);
ConstantSDNode *N0C = getAsNonOpaqueConstant(N0);
ConstantSDNode *N1C = getAsNonOpaqueConstant(N1);
if (N0C && N1C)
return DAG.FoldConstantArithmetic(ISD::XOR, SDLoc(N), VT, N0C, N1C);
// canonicalize constant to RHS
Expand Down Expand Up @@ -4019,15 +4045,13 @@ SDValue DAGCombiner::visitXOR(SDNode *N) {
}
// fold (xor (xor x, c1), c2) -> (xor x, (xor c1, c2))
if (N1C && N0.getOpcode() == ISD::XOR) {
ConstantSDNode *N00C = dyn_cast<ConstantSDNode>(N0.getOperand(0));
ConstantSDNode *N01C = dyn_cast<ConstantSDNode>(N0.getOperand(1));
if (N00C) {
if (const ConstantSDNode *N00C = getAsNonOpaqueConstant(N0.getOperand(0))) {
SDLoc DL(N);
return DAG.getNode(ISD::XOR, DL, VT, N0.getOperand(1),
DAG.getConstant(N1C->getAPIntValue() ^
N00C->getAPIntValue(), DL, VT));
}
if (N01C) {
if (const ConstantSDNode *N01C = getAsNonOpaqueConstant(N0.getOperand(1))) {
SDLoc DL(N);
return DAG.getNode(ISD::XOR, DL, VT, N0.getOperand(0),
DAG.getConstant(N1C->getAPIntValue() ^
Expand Down Expand Up @@ -4080,10 +4104,6 @@ SDValue DAGCombiner::visitXOR(SDNode *N) {
/// Handle transforms common to the three shifts, when the shift amount is a
/// constant.
SDValue DAGCombiner::visitShiftByConstant(SDNode *N, ConstantSDNode *Amt) {
// We can't and shouldn't fold opaque constants.
if (Amt->isOpaque())
return SDValue();

SDNode *LHS = N->getOperand(0).getNode();
if (!LHS->hasOneUse()) return SDValue();

Expand All @@ -4110,8 +4130,8 @@ SDValue DAGCombiner::visitShiftByConstant(SDNode *N, ConstantSDNode *Amt) {
}

// We require the RHS of the binop to be a constant and not opaque as well.
ConstantSDNode *BinOpCst = dyn_cast<ConstantSDNode>(LHS->getOperand(1));
if (!BinOpCst || BinOpCst->isOpaque()) return SDValue();
ConstantSDNode *BinOpCst = getAsNonOpaqueConstant(LHS->getOperand(1));
if (!BinOpCst) return SDValue();

// FIXME: disable this unless the input to the binop is a shift by a constant.
// If it is not a shift, it pessimizes some common cases like:
Expand Down Expand Up @@ -4164,15 +4184,17 @@ SDValue DAGCombiner::distributeTruncateThroughAnd(SDNode *N) {
SDValue N01 = N->getOperand(0).getOperand(1);

if (ConstantSDNode *N01C = isConstOrConstSplat(N01)) {
EVT TruncVT = N->getValueType(0);
SDValue N00 = N->getOperand(0).getOperand(0);
APInt TruncC = N01C->getAPIntValue();
TruncC = TruncC.trunc(TruncVT.getScalarSizeInBits());
SDLoc DL(N);
if (!N01C->isOpaque()) {
EVT TruncVT = N->getValueType(0);
SDValue N00 = N->getOperand(0).getOperand(0);
APInt TruncC = N01C->getAPIntValue();
TruncC = TruncC.trunc(TruncVT.getScalarSizeInBits());
SDLoc DL(N);

return DAG.getNode(ISD::AND, DL, TruncVT,
DAG.getNode(ISD::TRUNCATE, DL, TruncVT, N00),
DAG.getConstant(TruncC, DL, TruncVT));
return DAG.getNode(ISD::AND, DL, TruncVT,
DAG.getNode(ISD::TRUNCATE, DL, TruncVT, N00),
DAG.getConstant(TruncC, DL, TruncVT));
}
}
}

Expand Down Expand Up @@ -4226,8 +4248,8 @@ SDValue DAGCombiner::visitSHL(SDNode *N) {
}

// fold (shl c1, c2) -> c1<<c2
ConstantSDNode *N0C = dyn_cast<ConstantSDNode>(N0);
if (N0C && N1C)
ConstantSDNode *N0C = getAsNonOpaqueConstant(N0);
if (N0C && N1C && !N1C->isOpaque())
return DAG.FoldConstantArithmetic(ISD::SHL, SDLoc(N), VT, N0C, N1C);
// fold (shl 0, x) -> 0
if (isNullConstant(N0))
Expand Down Expand Up @@ -4372,7 +4394,7 @@ SDValue DAGCombiner::visitSHL(SDNode *N) {
return DAG.getNode(ISD::ADD, SDLoc(N), VT, Shl0, Shl1);
}

if (N1C) {
if (N1C && !N1C->isOpaque()) {
SDValue NewSHL = visitShiftByConstant(N, N1C);
if (NewSHL.getNode())
return NewSHL;
Expand All @@ -4397,8 +4419,8 @@ SDValue DAGCombiner::visitSRA(SDNode *N) {
}

// fold (sra c1, c2) -> (sra c1, c2)
ConstantSDNode *N0C = dyn_cast<ConstantSDNode>(N0);
if (N0C && N1C)
ConstantSDNode *N0C = getAsNonOpaqueConstant(N0);
if (N0C && N1C && !N1C->isOpaque())
return DAG.FoldConstantArithmetic(ISD::SRA, SDLoc(N), VT, N0C, N1C);
// fold (sra 0, x) -> 0
if (isNullConstant(N0))
Expand Down Expand Up @@ -4521,7 +4543,7 @@ SDValue DAGCombiner::visitSRA(SDNode *N) {
if (DAG.SignBitIsZero(N0))
return DAG.getNode(ISD::SRL, SDLoc(N), VT, N0, N1);

if (N1C) {
if (N1C && !N1C->isOpaque()) {
SDValue NewSRA = visitShiftByConstant(N, N1C);
if (NewSRA.getNode())
return NewSRA;
Expand All @@ -4546,8 +4568,8 @@ SDValue DAGCombiner::visitSRL(SDNode *N) {
}

// fold (srl c1, c2) -> c1 >>u c2
ConstantSDNode *N0C = dyn_cast<ConstantSDNode>(N0);
if (N0C && N1C)
ConstantSDNode *N0C = getAsNonOpaqueConstant(N0);
if (N0C && N1C && !N1C->isOpaque())
return DAG.FoldConstantArithmetic(ISD::SRL, SDLoc(N), VT, N0C, N1C);
// fold (srl 0, x) -> 0
if (isNullConstant(N0))
Expand Down Expand Up @@ -4692,7 +4714,7 @@ SDValue DAGCombiner::visitSRL(SDNode *N) {
if (N1C && SimplifyDemandedBits(SDValue(N, 0)))
return SDValue(N, 0);

if (N1C) {
if (N1C && !N1C->isOpaque()) {
SDValue NewSRL = visitShiftByConstant(N, N1C);
if (NewSRL.getNode())
return NewSRL;
Expand Down Expand Up @@ -6465,7 +6487,7 @@ SDValue DAGCombiner::GetDemandedBits(SDValue V, const APInt &Mask) {
// Only look at single-use SRLs.
if (!V.getNode()->hasOneUse())
break;
if (ConstantSDNode *RHSC = dyn_cast<ConstantSDNode>(V.getOperand(1))) {
if (ConstantSDNode *RHSC = getAsNonOpaqueConstant(V.getOperand(1))) {
// See if we can recursively simplify the LHS.
unsigned Amt = RHSC->getZExtValue();

Expand Down
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