[llvm-commits] CVS: llvm/lib/Target/TargetLowering.cpp
Nate Begeman
natebegeman at mac.com
Thu Feb 16 13:12:07 PST 2006
Changes in directory llvm/lib/Target:
TargetLowering.cpp updated: 1.30 -> 1.31
---
Log message:
Rework the SelectionDAG-based implementations of SimplifyDemandedBits
and ComputeMaskedBits to match the new improved versions in instcombine.
Tested against all of multisource/benchmarks on ppc.
---
Diffs of the changes: (+506 -122)
TargetLowering.cpp | 628 ++++++++++++++++++++++++++++++++++++++++++-----------
1 files changed, 506 insertions(+), 122 deletions(-)
Index: llvm/lib/Target/TargetLowering.cpp
diff -u llvm/lib/Target/TargetLowering.cpp:1.30 llvm/lib/Target/TargetLowering.cpp:1.31
--- llvm/lib/Target/TargetLowering.cpp:1.30 Tue Feb 14 02:38:30 2006
+++ llvm/lib/Target/TargetLowering.cpp Thu Feb 16 15:11:51 2006
@@ -135,175 +135,559 @@
// Optimization Methods
//===----------------------------------------------------------------------===//
-/// DemandedBitsAreZero - Return true if 'Op & Mask' demands no bits from a bit
-/// set operation such as a sign extend or or/xor with constant whose only
-/// use is Op. If it returns true, the old node that sets bits which are
-/// not demanded is returned in Old, and its replacement node is returned in
-/// New, such that callers of DemandedBitsAreZero may call CombineTo on them if
-/// desired.
-bool TargetLowering::DemandedBitsAreZero(const SDOperand &Op, uint64_t Mask,
- SDOperand &Old, SDOperand &New,
- SelectionDAG &DAG) const {
- // If the operation has more than one use, we're not interested in it.
- // Tracking down and checking all uses would be problematic and slow.
- if (!Op.Val->hasOneUse())
+/// ShrinkDemandedConstant - Check to see if the specified operand of the
+/// specified instruction is a constant integer. If so, check to see if there
+/// are any bits set in the constant that are not demanded. If so, shrink the
+/// constant and return true.
+bool TargetLowering::TargetLoweringOpt::ShrinkDemandedConstant(SDOperand Op,
+ uint64_t Demanded) {
+ // FIXME: ISD::SELECT
+ switch(Op.getOpcode()) {
+ default: break;
+ case ISD::AND:
+ case ISD::OR:
+ case ISD::XOR:
+ if (ConstantSDNode *C = dyn_cast<ConstantSDNode>(Op.getOperand(1)))
+ if ((~Demanded & C->getValue()) != 0) {
+ MVT::ValueType VT = Op.getValueType();
+ SDOperand New = DAG.getNode(Op.getOpcode(), VT, Op.getOperand(0),
+ DAG.getConstant(Demanded & C->getValue(),
+ VT));
+ return CombineTo(Op, New);
+ }
+ break;
+ }
+ return false;
+}
+
+/// SimplifyDemandedBits - Look at Op. At this point, we know that only the
+/// DemandedMask bits of the result of Op are ever used downstream. If we can
+/// use this information to simplify Op, create a new simplified DAG node and
+/// return true, returning the original and new nodes in Old and New. Otherwise,
+/// analyze the expression and return a mask of KnownOne and KnownZero bits for
+/// the expression (used to simplify the caller). The KnownZero/One bits may
+/// only be accurate for those bits in the DemandedMask.
+bool TargetLowering::SimplifyDemandedBits(SDOperand Op, uint64_t DemandedMask,
+ uint64_t &KnownZero,
+ uint64_t &KnownOne,
+ TargetLoweringOpt &TLO,
+ unsigned Depth) const {
+ KnownZero = KnownOne = 0; // Don't know anything.
+ // Other users may use these bits.
+ if (!Op.Val->hasOneUse()) {
+ if (Depth != 0) {
+ // If not at the root, Just compute the KnownZero/KnownOne bits to
+ // simplify things downstream.
+ ComputeMaskedBits(Op, DemandedMask, KnownZero, KnownOne, Depth);
+ return false;
+ }
+ // If this is the root being simplified, allow it to have multiple uses,
+ // just set the DemandedMask to all bits.
+ DemandedMask = MVT::getIntVTBitMask(Op.getValueType());
+ } else if (DemandedMask == 0) {
+ // Not demanding any bits from Op.
+ if (Op.getOpcode() != ISD::UNDEF)
+ return TLO.CombineTo(Op, TLO.DAG.getNode(ISD::UNDEF, Op.getValueType()));
return false;
-
+ } else if (Depth == 6) { // Limit search depth.
+ return false;
+ }
+
+ uint64_t KnownZero2, KnownOne2, KnownZeroOut, KnownOneOut;
switch (Op.getOpcode()) {
+ case ISD::Constant:
+ // We know all of the bits for a constant!
+ KnownOne = cast<ConstantSDNode>(Op)->getValue() & DemandedMask;
+ KnownZero = ~KnownOne & DemandedMask;
+ return false;
case ISD::AND:
- // (X & C1) & C2 == 0 iff C1 & C2 == 0.
- if (ConstantSDNode *AndRHS = dyn_cast<ConstantSDNode>(Op.getOperand(1))) {
- uint64_t NewVal = Mask & AndRHS->getValue();
- return DemandedBitsAreZero(Op.getOperand(0), NewVal, Old, New, DAG);
+ // If either the LHS or the RHS are Zero, the result is zero.
+ if (SimplifyDemandedBits(Op.getOperand(1), DemandedMask, KnownZero,
+ KnownOne, TLO, Depth+1))
+ return true;
+ assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
+ // If something is known zero on the RHS, the bits aren't demanded on the
+ // LHS.
+ if (SimplifyDemandedBits(Op.getOperand(0), DemandedMask & ~KnownZero,
+ KnownZero2, KnownOne2, TLO, Depth+1))
+ return true;
+ assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
+
+ // If all of the demanded bits are known one on one side, return the other.
+ // These bits cannot contribute to the result of the 'and'.
+ if ((DemandedMask & ~KnownZero2 & KnownOne)==(DemandedMask & ~KnownZero2))
+ return TLO.CombineTo(Op, Op.getOperand(0));
+ if ((DemandedMask & ~KnownZero & KnownOne2)==(DemandedMask & ~KnownZero))
+ return TLO.CombineTo(Op, Op.getOperand(1));
+ // If all of the demanded bits in the inputs are known zeros, return zero.
+ if ((DemandedMask & (KnownZero|KnownZero2)) == DemandedMask)
+ return TLO.CombineTo(Op, TLO.DAG.getConstant(0, Op.getValueType()));
+ // If the RHS is a constant, see if we can simplify it.
+ if (TLO.ShrinkDemandedConstant(Op, DemandedMask & ~KnownZero2))
+ return true;
+
+ // Output known-1 bits are only known if set in both the LHS & RHS.
+ KnownOne &= KnownOne2;
+ // Output known-0 are known to be clear if zero in either the LHS | RHS.
+ KnownZero |= KnownZero2;
+ break;
+ case ISD::OR:
+ if (SimplifyDemandedBits(Op.getOperand(1), DemandedMask, KnownZero,
+ KnownOne, TLO, Depth+1))
+ return true;
+ assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
+ if (SimplifyDemandedBits(Op.getOperand(0), DemandedMask & ~KnownOne,
+ KnownZero2, KnownOne2, TLO, Depth+1))
+ return true;
+ assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
+
+ // If all of the demanded bits are known zero on one side, return the other.
+ // These bits cannot contribute to the result of the 'or'.
+ if ((DemandedMask & ~KnownOne2 & KnownZero) == DemandedMask & ~KnownOne2)
+ return TLO.CombineTo(Op, Op.getOperand(0));
+ if ((DemandedMask & ~KnownOne & KnownZero2) == DemandedMask & ~KnownOne)
+ return TLO.CombineTo(Op, Op.getOperand(1));
+ // If all of the potentially set bits on one side are known to be set on
+ // the other side, just use the 'other' side.
+ if ((DemandedMask & (~KnownZero) & KnownOne2) ==
+ (DemandedMask & (~KnownZero)))
+ return TLO.CombineTo(Op, Op.getOperand(0));
+ if ((DemandedMask & (~KnownZero2) & KnownOne) ==
+ (DemandedMask & (~KnownZero2)))
+ return TLO.CombineTo(Op, Op.getOperand(1));
+ // If the RHS is a constant, see if we can simplify it.
+ if (TLO.ShrinkDemandedConstant(Op, DemandedMask))
+ return true;
+
+ // Output known-0 bits are only known if clear in both the LHS & RHS.
+ KnownZero &= KnownZero2;
+ // Output known-1 are known to be set if set in either the LHS | RHS.
+ KnownOne |= KnownOne2;
+ break;
+ case ISD::XOR:
+ if (SimplifyDemandedBits(Op.getOperand(1), DemandedMask, KnownZero,
+ KnownOne, TLO, Depth+1))
+ return true;
+ assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
+ if (SimplifyDemandedBits(Op.getOperand(0), DemandedMask, KnownZero2,
+ KnownOne2, TLO, Depth+1))
+ return true;
+ assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
+
+ // If all of the demanded bits are known zero on one side, return the other.
+ // These bits cannot contribute to the result of the 'xor'.
+ if ((DemandedMask & KnownZero) == DemandedMask)
+ return TLO.CombineTo(Op, Op.getOperand(0));
+ if ((DemandedMask & KnownZero2) == DemandedMask)
+ return TLO.CombineTo(Op, Op.getOperand(1));
+
+ // Output known-0 bits are known if clear or set in both the LHS & RHS.
+ KnownZeroOut = (KnownZero & KnownZero2) | (KnownOne & KnownOne2);
+ // Output known-1 are known to be set if set in only one of the LHS, RHS.
+ KnownOneOut = (KnownZero & KnownOne2) | (KnownOne & KnownZero2);
+
+ // If all of the unknown bits are known to be zero on one side or the other
+ // (but not both) turn this into an *inclusive* or.
+ // e.g. (A & C1)^(B & C2) -> (A & C1)|(B & C2) iff C1&C2 == 0
+ if (uint64_t UnknownBits = DemandedMask & ~(KnownZeroOut|KnownOneOut))
+ if ((UnknownBits & (KnownZero|KnownZero2)) == UnknownBits)
+ return TLO.CombineTo(Op, TLO.DAG.getNode(ISD::OR, Op.getValueType(),
+ Op.getOperand(0),
+ Op.getOperand(1)));
+ // If all of the demanded bits on one side are known, and all of the set
+ // bits on that side are also known to be set on the other side, turn this
+ // into an AND, as we know the bits will be cleared.
+ // e.g. (X | C1) ^ C2 --> (X | C1) & ~C2 iff (C1&C2) == C2
+ if ((DemandedMask & (KnownZero|KnownOne)) == DemandedMask) { // all known
+ if ((KnownOne & KnownOne2) == KnownOne) {
+ MVT::ValueType VT = Op.getValueType();
+ SDOperand ANDC = TLO.DAG.getConstant(~KnownOne & DemandedMask, VT);
+ return TLO.CombineTo(Op, TLO.DAG.getNode(ISD::AND, VT, Op.getOperand(0),
+ ANDC));
+ }
}
+
+ // If the RHS is a constant, see if we can simplify it.
+ // FIXME: for XOR, we prefer to force bits to 1 if they will make a -1.
+ if (TLO.ShrinkDemandedConstant(Op, DemandedMask))
+ return true;
+
+ KnownZero = KnownZeroOut;
+ KnownOne = KnownOneOut;
+ break;
+ case ISD::SETCC:
+ // If we know the result of a setcc has the top bits zero, use this info.
+ if (getSetCCResultContents() == TargetLowering::ZeroOrOneSetCCResult)
+ KnownZero |= (MVT::getIntVTBitMask(Op.getValueType()) ^ 1ULL);
+ break;
+ case ISD::SELECT:
+ if (SimplifyDemandedBits(Op.getOperand(2), DemandedMask, KnownZero,
+ KnownOne, TLO, Depth+1))
+ return true;
+ if (SimplifyDemandedBits(Op.getOperand(1), DemandedMask, KnownZero2,
+ KnownOne2, TLO, Depth+1))
+ return true;
+ assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
+ assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
+
+ // If the operands are constants, see if we can simplify them.
+ if (TLO.ShrinkDemandedConstant(Op, DemandedMask))
+ return true;
+
+ // Only known if known in both the LHS and RHS.
+ KnownOne &= KnownOne2;
+ KnownZero &= KnownZero2;
break;
case ISD::SHL:
- // (ushl X, C1) & C2 == 0 iff X & (C2 >> C1) == 0
- if (ConstantSDNode *ShAmt = dyn_cast<ConstantSDNode>(Op.getOperand(1))) {
- uint64_t NewVal = Mask >> ShAmt->getValue();
- return DemandedBitsAreZero(Op.getOperand(0), NewVal, Old, New, DAG);
+ if (ConstantSDNode *SA = dyn_cast<ConstantSDNode>(Op.getOperand(1))) {
+ if (SimplifyDemandedBits(Op.getOperand(0), DemandedMask >> SA->getValue(),
+ KnownZero, KnownOne, TLO, Depth+1))
+ return true;
+ KnownZero <<= SA->getValue();
+ KnownOne <<= SA->getValue();
+ KnownZero |= (1ULL << SA->getValue())-1; // low bits known zero.
+ }
+ break;
+ case ISD::SRL:
+ if (ConstantSDNode *SA = dyn_cast<ConstantSDNode>(Op.getOperand(1))) {
+ MVT::ValueType VT = Op.getValueType();
+ unsigned ShAmt = SA->getValue();
+
+ // Compute the new bits that are at the top now.
+ uint64_t HighBits = (1ULL << ShAmt)-1;
+ HighBits <<= MVT::getSizeInBits(VT) - ShAmt;
+ uint64_t TypeMask = MVT::getIntVTBitMask(VT);
+
+ if (SimplifyDemandedBits(Op.getOperand(0),
+ (DemandedMask << ShAmt) & TypeMask,
+ KnownZero, KnownOne, TLO, Depth+1))
+ return true;
+ assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
+ KnownZero &= TypeMask;
+ KnownOne &= TypeMask;
+ KnownZero >>= ShAmt;
+ KnownOne >>= ShAmt;
+ KnownZero |= HighBits; // high bits known zero.
+ }
+ break;
+ case ISD::SRA:
+ if (ConstantSDNode *SA = dyn_cast<ConstantSDNode>(Op.getOperand(1))) {
+ MVT::ValueType VT = Op.getValueType();
+ unsigned ShAmt = SA->getValue();
+
+ // Compute the new bits that are at the top now.
+ uint64_t HighBits = (1ULL << ShAmt)-1;
+ HighBits <<= MVT::getSizeInBits(VT) - ShAmt;
+ uint64_t TypeMask = MVT::getIntVTBitMask(VT);
+
+ if (SimplifyDemandedBits(Op.getOperand(0),
+ (DemandedMask << ShAmt) & TypeMask,
+ KnownZero, KnownOne, TLO, Depth+1))
+ return true;
+ assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
+ KnownZero &= TypeMask;
+ KnownOne &= TypeMask;
+ KnownZero >>= SA->getValue();
+ KnownOne >>= SA->getValue();
+
+ // Handle the sign bits.
+ uint64_t SignBit = MVT::getIntVTSignBit(VT);
+ SignBit >>= SA->getValue(); // Adjust to where it is now in the mask.
+
+ // If the input sign bit is known to be zero, or if none of the top bits
+ // are demanded, turn this into an unsigned shift right.
+ if ((KnownZero & SignBit) || (HighBits & ~DemandedMask) == HighBits) {
+ return TLO.CombineTo(Op, TLO.DAG.getNode(ISD::SRL, VT, Op.getOperand(0),
+ Op.getOperand(1)));
+ } else if (KnownOne & SignBit) { // New bits are known one.
+ KnownOne |= HighBits;
+ }
}
break;
case ISD::SIGN_EXTEND_INREG: {
+ MVT::ValueType VT = Op.getValueType();
MVT::ValueType EVT = cast<VTSDNode>(Op.getOperand(1))->getVT();
- unsigned ExtendBits = MVT::getSizeInBits(EVT);
- // If we're extending from something smaller than MVT::i64 and all of the
- // sign extension bits are masked, return true and set New to be the
- // first operand, since we no longer care what the high bits are.
- if (ExtendBits < 64 && ((Mask & (~0ULL << ExtendBits)) == 0)) {
- Old = Op;
- New = Op.getOperand(0);
+
+ // Sign or Zero extension. Compute the bits in the result that are not
+ // present in the input.
+ uint64_t NotIn = ~MVT::getIntVTBitMask(EVT);
+ uint64_t NewBits = MVT::getIntVTBitMask(VT) & NotIn;
+
+ // Sign extension.
+ uint64_t InSignBit = MVT::getIntVTSignBit(EVT);
+ int64_t InputDemandedBits = DemandedMask & MVT::getIntVTBitMask(EVT);
+
+ // If any of the sign extended bits are demanded, we know that the sign
+ // bit is demanded.
+ if (NewBits & DemandedMask)
+ InputDemandedBits |= InSignBit;
+
+ if (SimplifyDemandedBits(Op.getOperand(0), InputDemandedBits,
+ KnownZero, KnownOne, TLO, Depth+1))
return true;
+ assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
+
+ // If the sign bit of the input is known set or clear, then we know the
+ // top bits of the result.
+
+ // If the input sign bit is known zero, or if the NewBits are not demanded
+ // convert this into a zero extension.
+ if ((KnownZero & InSignBit) || (NewBits & ~DemandedMask) == NewBits) {
+ return TLO.CombineTo(Op, Op.getOperand(0));
+ } else if (KnownOne & InSignBit) { // Input sign bit known set
+ KnownOne |= NewBits;
+ KnownZero &= ~NewBits;
+ } else { // Input sign bit unknown
+ KnownZero &= ~NewBits;
+ KnownOne &= ~NewBits;
}
break;
}
- case ISD::SRA:
- if (ConstantSDNode *ShAmt = dyn_cast<ConstantSDNode>(Op.getOperand(1))) {
- unsigned OpBits = MVT::getSizeInBits(Op.getValueType());
- unsigned SH = ShAmt->getValue();
- if (SH && ((Mask & (~0ULL << (OpBits-SH))) == 0)) {
- Old = Op;
- New = DAG.getNode(ISD::SRL, Op.getValueType(), Op.getOperand(0),
- Op.getOperand(1));
+ case ISD::ADD:
+ if (ConstantSDNode *AA = dyn_cast<ConstantSDNode>(Op.getOperand(1))) {
+ if (SimplifyDemandedBits(Op.getOperand(0), DemandedMask, KnownZero,
+ KnownOne, TLO, Depth+1))
return true;
- }
+ // Compute the KnownOne/KnownZero masks for the constant, so we can set
+ // KnownZero appropriately if we're adding a constant that has all low
+ // bits cleared.
+ ComputeMaskedBits(Op.getOperand(1),
+ MVT::getIntVTBitMask(Op.getValueType()),
+ KnownZero2, KnownOne2, Depth+1);
+
+ uint64_t KnownZeroOut = std::min(CountTrailingZeros_64(~KnownZero),
+ CountTrailingZeros_64(~KnownZero2));
+ KnownZero = (1ULL << KnownZeroOut) - 1;
+ KnownOne = 0;
}
break;
+ case ISD::CTTZ:
+ case ISD::CTLZ:
+ case ISD::CTPOP: {
+ MVT::ValueType VT = Op.getValueType();
+ unsigned LowBits = Log2_32(MVT::getSizeInBits(VT))+1;
+ KnownZero = ~((1ULL << LowBits)-1) & MVT::getIntVTBitMask(VT);
+ KnownOne = 0;
+ break;
+ }
}
return false;
}
-/// MaskedValueIsZero - Return true if 'Op & Mask' is known to be zero. We use
-/// this predicate to simplify operations downstream. Op and Mask are known to
-/// be the same type.
-bool TargetLowering::MaskedValueIsZero(const SDOperand &Op,
- uint64_t Mask) const {
- unsigned SrcBits;
- if (Mask == 0) return true;
+/// MaskedValueIsZero - Return true if 'V & Mask' is known to be zero. We use
+/// this predicate to simplify operations downstream. Mask is known to be zero
+/// for bits that V cannot have.
+bool TargetLowering::MaskedValueIsZero(SDOperand Op, uint64_t Mask,
+ unsigned Depth) const {
+ uint64_t KnownZero, KnownOne;
+ ComputeMaskedBits(Op, Mask, KnownZero, KnownOne, Depth);
+ assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
+ return (KnownZero & Mask) == Mask;
+}
+
+/// ComputeMaskedBits - Determine which of the bits specified in Mask are
+/// known to be either zero or one and return them in the KnownZero/KnownOne
+/// bitsets. This code only analyzes bits in Mask, in order to short-circuit
+/// processing.
+void TargetLowering::ComputeMaskedBits(SDOperand Op, uint64_t Mask,
+ uint64_t &KnownZero, uint64_t &KnownOne,
+ unsigned Depth) const {
+ KnownZero = KnownOne = 0; // Don't know anything.
+ if (Depth == 6 || Mask == 0)
+ return; // Limit search depth.
- // If we know the result of a setcc has the top bits zero, use this info.
+ uint64_t KnownZero2, KnownOne2;
+
switch (Op.getOpcode()) {
case ISD::Constant:
- return (cast<ConstantSDNode>(Op)->getValue() & Mask) == 0;
- case ISD::SETCC:
- return ((Mask & 1) == 0) &&
- getSetCCResultContents() == TargetLowering::ZeroOrOneSetCCResult;
- case ISD::ZEXTLOAD:
- SrcBits = MVT::getSizeInBits(cast<VTSDNode>(Op.getOperand(3))->getVT());
- return (Mask & ((1ULL << SrcBits)-1)) == 0; // Returning only the zext bits.
- case ISD::ZERO_EXTEND:
- SrcBits = MVT::getSizeInBits(Op.getOperand(0).getValueType());
- return MaskedValueIsZero(Op.getOperand(0),Mask & (~0ULL >> (64-SrcBits)));
- case ISD::ANY_EXTEND:
- // If the mask only includes bits in the low part, recurse.
- SrcBits = MVT::getSizeInBits(Op.getOperand(0).getValueType());
- if (Mask >> SrcBits) return false; // Use of unknown top bits.
- return MaskedValueIsZero(Op.getOperand(0), Mask);
- case ISD::AssertZext:
- SrcBits = MVT::getSizeInBits(cast<VTSDNode>(Op.getOperand(1))->getVT());
- return (Mask & ((1ULL << SrcBits)-1)) == 0; // Returning only the zext bits.
+ // We know all of the bits for a constant!
+ KnownOne = cast<ConstantSDNode>(Op)->getValue() & Mask;
+ KnownZero = ~KnownOne & Mask;
+ return;
case ISD::AND:
- // If either of the operands has zero bits, the result will too.
- if (MaskedValueIsZero(Op.getOperand(1), Mask) ||
- MaskedValueIsZero(Op.getOperand(0), Mask))
- return true;
- // (X & C1) & C2 == 0 iff C1 & C2 == 0.
- if (ConstantSDNode *AndRHS = dyn_cast<ConstantSDNode>(Op.getOperand(1)))
- return MaskedValueIsZero(Op.getOperand(0),AndRHS->getValue() & Mask);
- return false;
+ // If either the LHS or the RHS are Zero, the result is zero.
+ ComputeMaskedBits(Op.getOperand(1), Mask, KnownZero, KnownOne, Depth+1);
+ Mask &= ~KnownZero;
+ ComputeMaskedBits(Op.getOperand(0), Mask, KnownZero2, KnownOne2, Depth+1);
+ assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
+ assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
+
+ // Output known-1 bits are only known if set in both the LHS & RHS.
+ KnownOne &= KnownOne2;
+ // Output known-0 are known to be clear if zero in either the LHS | RHS.
+ KnownZero |= KnownZero2;
+ return;
case ISD::OR:
- case ISD::XOR:
- return MaskedValueIsZero(Op.getOperand(0), Mask) &&
- MaskedValueIsZero(Op.getOperand(1), Mask);
+ ComputeMaskedBits(Op.getOperand(1), Mask, KnownZero, KnownOne, Depth+1);
+ Mask &= ~KnownOne;
+ ComputeMaskedBits(Op.getOperand(0), Mask, KnownZero2, KnownOne2, Depth+1);
+ assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
+ assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
+
+ // Output known-0 bits are only known if clear in both the LHS & RHS.
+ KnownZero &= KnownZero2;
+ // Output known-1 are known to be set if set in either the LHS | RHS.
+ KnownOne |= KnownOne2;
+ return;
+ case ISD::XOR: {
+ ComputeMaskedBits(Op.getOperand(1), Mask, KnownZero, KnownOne, Depth+1);
+ ComputeMaskedBits(Op.getOperand(0), Mask, KnownZero2, KnownOne2, Depth+1);
+ assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
+ assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
+
+ // Output known-0 bits are known if clear or set in both the LHS & RHS.
+ uint64_t KnownZeroOut = (KnownZero & KnownZero2) | (KnownOne & KnownOne2);
+ // Output known-1 are known to be set if set in only one of the LHS, RHS.
+ KnownOne = (KnownZero & KnownOne2) | (KnownOne & KnownZero2);
+ KnownZero = KnownZeroOut;
+ return;
+ }
case ISD::SELECT:
- return MaskedValueIsZero(Op.getOperand(1), Mask) &&
- MaskedValueIsZero(Op.getOperand(2), Mask);
+ ComputeMaskedBits(Op.getOperand(2), Mask, KnownZero, KnownOne, Depth+1);
+ ComputeMaskedBits(Op.getOperand(1), Mask, KnownZero2, KnownOne2, Depth+1);
+ assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
+ assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
+
+ // Only known if known in both the LHS and RHS.
+ KnownOne &= KnownOne2;
+ KnownZero &= KnownZero2;
+ return;
case ISD::SELECT_CC:
- return MaskedValueIsZero(Op.getOperand(2), Mask) &&
- MaskedValueIsZero(Op.getOperand(3), Mask);
- case ISD::SRL:
- // (ushr X, C1) & C2 == 0 iff X & (C2 << C1) == 0
- if (ConstantSDNode *ShAmt = dyn_cast<ConstantSDNode>(Op.getOperand(1))) {
- uint64_t NewVal = Mask << ShAmt->getValue();
- SrcBits = MVT::getSizeInBits(Op.getValueType());
- if (SrcBits != 64) NewVal &= (1ULL << SrcBits)-1;
- return MaskedValueIsZero(Op.getOperand(0), NewVal);
- }
- return false;
+ ComputeMaskedBits(Op.getOperand(3), Mask, KnownZero, KnownOne, Depth+1);
+ ComputeMaskedBits(Op.getOperand(2), Mask, KnownZero2, KnownOne2, Depth+1);
+ assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
+ assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
+
+ // Only known if known in both the LHS and RHS.
+ KnownOne &= KnownOne2;
+ KnownZero &= KnownZero2;
+ return;
+ case ISD::SETCC:
+ // If we know the result of a setcc has the top bits zero, use this info.
+ if (getSetCCResultContents() == TargetLowering::ZeroOrOneSetCCResult)
+ KnownZero |= (MVT::getIntVTBitMask(Op.getValueType()) ^ 1ULL);
+ return;
case ISD::SHL:
- // (ushl X, C1) & C2 == 0 iff X & (C2 >> C1) == 0
- if (ConstantSDNode *ShAmt = dyn_cast<ConstantSDNode>(Op.getOperand(1))) {
- uint64_t NewVal = Mask >> ShAmt->getValue();
- return MaskedValueIsZero(Op.getOperand(0), NewVal);
+ // (shl X, C1) & C2 == 0 iff (X & C2 >>u C1) == 0
+ if (ConstantSDNode *SA = dyn_cast<ConstantSDNode>(Op.getOperand(1))) {
+ Mask >>= SA->getValue();
+ ComputeMaskedBits(Op.getOperand(0), Mask, KnownZero, KnownOne, Depth+1);
+ assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
+ KnownZero <<= SA->getValue();
+ KnownOne <<= SA->getValue();
+ KnownZero |= (1ULL << SA->getValue())-1; // low bits known zero.
}
- return false;
- case ISD::ADD:
- // (add X, Y) & C == 0 iff (X&C)|(Y&C) == 0 and all bits are low bits.
- if ((Mask&(Mask+1)) == 0) { // All low bits
- if (MaskedValueIsZero(Op.getOperand(0), Mask) &&
- MaskedValueIsZero(Op.getOperand(1), Mask))
- return true;
+ break;
+ case ISD::SRL:
+ // (ushr X, C1) & C2 == 0 iff (-1 >> C1) & C2 == 0
+ if (ConstantSDNode *SA = dyn_cast<ConstantSDNode>(Op.getOperand(1))) {
+ uint64_t HighBits = (1ULL << SA->getValue())-1;
+ HighBits <<= MVT::getSizeInBits(Op.getValueType())-SA->getValue();
+ Mask <<= SA->getValue();
+ ComputeMaskedBits(Op.getOperand(0), Mask, KnownZero, KnownOne, Depth+1);
+ assert((KnownZero & KnownOne) == 0&&"Bits known to be one AND zero?");
+ KnownZero >>= SA->getValue();
+ KnownOne >>= SA->getValue();
+ KnownZero |= HighBits; // high bits known zero.
}
break;
- case ISD::SUB:
- if (ConstantSDNode *CLHS = dyn_cast<ConstantSDNode>(Op.getOperand(0))) {
- // We know that the top bits of C-X are clear if X contains less bits
- // than C (i.e. no wrap-around can happen). For example, 20-X is
- // positive if we can prove that X is >= 0 and < 16.
- unsigned Bits = MVT::getSizeInBits(CLHS->getValueType(0));
- if ((CLHS->getValue() & (1 << (Bits-1))) == 0) { // sign bit clear
- unsigned NLZ = CountLeadingZeros_64(CLHS->getValue()+1);
- uint64_t MaskV = (1ULL << (63-NLZ))-1;
- if (MaskedValueIsZero(Op.getOperand(1), ~MaskV)) {
- // High bits are clear this value is known to be >= C.
- unsigned NLZ2 = CountLeadingZeros_64(CLHS->getValue());
- if ((Mask & ((1ULL << (64-NLZ2))-1)) == 0)
- return true;
- }
+ case ISD::SRA:
+ if (ConstantSDNode *SA = dyn_cast<ConstantSDNode>(Op.getOperand(1))) {
+ uint64_t HighBits = (1ULL << SA->getValue())-1;
+ HighBits <<= MVT::getSizeInBits(Op.getValueType())-SA->getValue();
+ Mask <<= SA->getValue();
+ ComputeMaskedBits(Op.getOperand(0), Mask, KnownZero, KnownOne, Depth+1);
+ assert((KnownZero & KnownOne) == 0&&"Bits known to be one AND zero?");
+ KnownZero >>= SA->getValue();
+ KnownOne >>= SA->getValue();
+
+ // Handle the sign bits.
+ uint64_t SignBit = 1ULL << (MVT::getSizeInBits(Op.getValueType())-1);
+ SignBit >>= SA->getValue(); // Adjust to where it is now in the mask.
+
+ if (KnownZero & SignBit) { // New bits are known zero.
+ KnownZero |= HighBits;
+ } else if (KnownOne & SignBit) { // New bits are known one.
+ KnownOne |= HighBits;
}
}
break;
case ISD::CTTZ:
case ISD::CTLZ:
- case ISD::CTPOP:
- // Bit counting instructions can not set the high bits of the result
- // register. The max number of bits sets depends on the input.
- return (Mask & (MVT::getSizeInBits(Op.getValueType())*2-1)) == 0;
+ case ISD::CTPOP: {
+ MVT::ValueType VT = Op.getValueType();
+ unsigned LowBits = Log2_32(MVT::getSizeInBits(VT))+1;
+ KnownZero = ~((1ULL << LowBits)-1) & MVT::getIntVTBitMask(VT);
+ KnownOne = 0;
+ return;
+ }
+ case ISD::ZEXTLOAD: {
+ unsigned SrcBits =
+ MVT::getSizeInBits(cast<VTSDNode>(Op.getOperand(3))->getVT());
+ KnownZero |= ~((1ULL << SrcBits)-1);
+ return;
+ }
+ case ISD::ZERO_EXTEND: {
+ unsigned SrcBits =
+ MVT::getSizeInBits(Op.getOperand(0).getValueType());
+ KnownZero |= ~((1ULL << SrcBits)-1);
+ return;
+ }
+ case ISD::ANY_EXTEND: {
+ unsigned SrcBits =
+ MVT::getSizeInBits(Op.getOperand(0).getValueType());
+ KnownZero &= ((1ULL << SrcBits)-1);
+ KnownOne &= ((1ULL << SrcBits)-1);
+ return;
+ }
+ case ISD::AssertZext: {
+ unsigned SrcBits =
+ MVT::getSizeInBits(cast<VTSDNode>(Op.getOperand(1))->getVT());
+ KnownZero |= ~((1ULL << SrcBits)-1);
+ return;
+ }
+ case ISD::ADD: {
+ // If either the LHS or the RHS are Zero, the result is zero.
+ ComputeMaskedBits(Op.getOperand(1), Mask, KnownZero, KnownOne, Depth+1);
+ ComputeMaskedBits(Op.getOperand(0), Mask, KnownZero2, KnownOne2, Depth+1);
+ assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
+ assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
+
+ // Output known-0 bits are known if clear or set in both the low clear bits
+ // common to both LHS & RHS;
+ uint64_t KnownZeroOut = std::min(CountTrailingZeros_64(~KnownZero),
+ CountTrailingZeros_64(~KnownZero2));
+
+ KnownZero = (1ULL << KnownZeroOut) - 1;
+ KnownOne = 0;
+ return;
+ }
+ case ISD::SUB:
+ // We know that the top bits of C-X are clear if X contains less bits
+ // than C (i.e. no wrap-around can happen). For example, 20-X is
+ // positive if we can prove that X is >= 0 and < 16.
+ break;
default:
// Allow the target to implement this method for its nodes.
if (Op.getOpcode() >= ISD::BUILTIN_OP_END)
- return isMaskedValueZeroForTargetNode(Op, Mask);
+ computeMaskedBitsForTargetNode(Op, Mask, KnownZero, KnownOne);
break;
}
- return false;
}
-bool TargetLowering::isMaskedValueZeroForTargetNode(const SDOperand &Op,
- uint64_t Mask) const {
+/// computeMaskedBitsForTargetNode - Determine which of the bits specified
+/// in Mask are known to be either zero or one and return them in the
+/// KnownZero/KnownOne bitsets.
+void TargetLowering::computeMaskedBitsForTargetNode(const SDOperand Op,
+ uint64_t Mask,
+ uint64_t &KnownZero,
+ uint64_t &KnownOne,
+ unsigned Depth) const {
assert(Op.getOpcode() >= ISD::BUILTIN_OP_END &&
"Should use MaskedValueIsZero if you don't know whether Op"
" is a target node!");
- return false;
+ KnownZero = 0;
+ KnownOne = 0;
}
//===----------------------------------------------------------------------===//
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