//===- InstCombineSimplifyDemanded.cpp ------------------------------------===// // // The LLVM Compiler Infrastructure // // This file is distributed under the University of Illinois Open Source // License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// // // This file contains logic for simplifying instructions based on information // about how they are used. // //===----------------------------------------------------------------------===// #include "InstCombine.h" #include "llvm/Target/TargetData.h" #include "llvm/IntrinsicInst.h" using namespace llvm; /// 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. static bool ShrinkDemandedConstant(Instruction *I, unsigned OpNo, APInt Demanded) { assert(I && "No instruction?"); assert(OpNo < I->getNumOperands() && "Operand index too large"); // If the operand is not a constant integer, nothing to do. ConstantInt *OpC = dyn_cast(I->getOperand(OpNo)); if (!OpC) return false; // If there are no bits set that aren't demanded, nothing to do. Demanded.zextOrTrunc(OpC->getValue().getBitWidth()); if ((~Demanded & OpC->getValue()) == 0) return false; // This instruction is producing bits that are not demanded. Shrink the RHS. Demanded &= OpC->getValue(); I->setOperand(OpNo, ConstantInt::get(OpC->getType(), Demanded)); return true; } /// SimplifyDemandedInstructionBits - Inst is an integer instruction that /// SimplifyDemandedBits knows about. See if the instruction has any /// properties that allow us to simplify its operands. bool InstCombiner::SimplifyDemandedInstructionBits(Instruction &Inst) { unsigned BitWidth = Inst.getType()->getScalarSizeInBits(); APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0); APInt DemandedMask(APInt::getAllOnesValue(BitWidth)); Value *V = SimplifyDemandedUseBits(&Inst, DemandedMask, KnownZero, KnownOne, 0); if (V == 0) return false; if (V == &Inst) return true; ReplaceInstUsesWith(Inst, V); return true; } /// SimplifyDemandedBits - This form of SimplifyDemandedBits simplifies the /// specified instruction operand if possible, updating it in place. It returns /// true if it made any change and false otherwise. bool InstCombiner::SimplifyDemandedBits(Use &U, APInt DemandedMask, APInt &KnownZero, APInt &KnownOne, unsigned Depth) { Value *NewVal = SimplifyDemandedUseBits(U.get(), DemandedMask, KnownZero, KnownOne, Depth); if (NewVal == 0) return false; U = NewVal; return true; } /// SimplifyDemandedUseBits - This function attempts to replace V with a simpler /// value based on the demanded bits. When this function is called, it is known /// that only the bits set in DemandedMask of the result of V are ever used /// downstream. Consequently, depending on the mask and V, it may be possible /// to replace V with a constant or one of its operands. In such cases, this /// function does the replacement and returns true. In all other cases, it /// returns false after analyzing the expression and setting KnownOne and known /// to be one in the expression. KnownZero contains all the bits that are known /// to be zero in the expression. These are provided to potentially allow the /// caller (which might recursively be SimplifyDemandedBits itself) to simplify /// the expression. KnownOne and KnownZero always follow the invariant that /// KnownOne & KnownZero == 0. That is, a bit can't be both 1 and 0. Note that /// the bits in KnownOne and KnownZero may only be accurate for those bits set /// in DemandedMask. Note also that the bitwidth of V, DemandedMask, KnownZero /// and KnownOne must all be the same. /// /// This returns null if it did not change anything and it permits no /// simplification. This returns V itself if it did some simplification of V's /// operands based on the information about what bits are demanded. This returns /// some other non-null value if it found out that V is equal to another value /// in the context where the specified bits are demanded, but not for all users. Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask, APInt &KnownZero, APInt &KnownOne, unsigned Depth) { assert(V != 0 && "Null pointer of Value???"); assert(Depth <= 6 && "Limit Search Depth"); uint32_t BitWidth = DemandedMask.getBitWidth(); const Type *VTy = V->getType(); assert((TD || !VTy->isPointerTy()) && "SimplifyDemandedBits needs to know bit widths!"); assert((!TD || TD->getTypeSizeInBits(VTy->getScalarType()) == BitWidth) && (!VTy->isIntOrIntVectorTy() || VTy->getScalarSizeInBits() == BitWidth) && KnownZero.getBitWidth() == BitWidth && KnownOne.getBitWidth() == BitWidth && "Value *V, DemandedMask, KnownZero and KnownOne " "must have same BitWidth"); if (ConstantInt *CI = dyn_cast(V)) { // We know all of the bits for a constant! KnownOne = CI->getValue() & DemandedMask; KnownZero = ~KnownOne & DemandedMask; return 0; } if (isa(V)) { // We know all of the bits for a constant! KnownOne.clear(); KnownZero = DemandedMask; return 0; } KnownZero.clear(); KnownOne.clear(); if (DemandedMask == 0) { // Not demanding any bits from V. if (isa(V)) return 0; return UndefValue::get(VTy); } if (Depth == 6) // Limit search depth. return 0; APInt LHSKnownZero(BitWidth, 0), LHSKnownOne(BitWidth, 0); APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0); Instruction *I = dyn_cast(V); if (!I) { ComputeMaskedBits(V, DemandedMask, KnownZero, KnownOne, Depth); return 0; // Only analyze instructions. } // If there are multiple uses of this value and we aren't at the root, then // we can't do any simplifications of the operands, because DemandedMask // only reflects the bits demanded by *one* of the users. if (Depth != 0 && !I->hasOneUse()) { // Despite the fact that we can't simplify this instruction in all User's // context, we can at least compute the knownzero/knownone bits, and we can // do simplifications that apply to *just* the one user if we know that // this instruction has a simpler value in that context. if (I->getOpcode() == Instruction::And) { // If either the LHS or the RHS are Zero, the result is zero. ComputeMaskedBits(I->getOperand(1), DemandedMask, RHSKnownZero, RHSKnownOne, Depth+1); ComputeMaskedBits(I->getOperand(0), DemandedMask & ~RHSKnownZero, LHSKnownZero, LHSKnownOne, Depth+1); // If all of the demanded bits are known 1 on one side, return the other. // These bits cannot contribute to the result of the 'and' in this // context. if ((DemandedMask & ~LHSKnownZero & RHSKnownOne) == (DemandedMask & ~LHSKnownZero)) return I->getOperand(0); if ((DemandedMask & ~RHSKnownZero & LHSKnownOne) == (DemandedMask & ~RHSKnownZero)) return I->getOperand(1); // If all of the demanded bits in the inputs are known zeros, return zero. if ((DemandedMask & (RHSKnownZero|LHSKnownZero)) == DemandedMask) return Constant::getNullValue(VTy); } else if (I->getOpcode() == Instruction::Or) { // We can simplify (X|Y) -> X or Y in the user's context if we know that // only bits from X or Y are demanded. // If either the LHS or the RHS are One, the result is One. ComputeMaskedBits(I->getOperand(1), DemandedMask, RHSKnownZero, RHSKnownOne, Depth+1); ComputeMaskedBits(I->getOperand(0), DemandedMask & ~RHSKnownOne, LHSKnownZero, LHSKnownOne, Depth+1); // 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' in this // context. if ((DemandedMask & ~LHSKnownOne & RHSKnownZero) == (DemandedMask & ~LHSKnownOne)) return I->getOperand(0); if ((DemandedMask & ~RHSKnownOne & LHSKnownZero) == (DemandedMask & ~RHSKnownOne)) return I->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 & (~RHSKnownZero) & LHSKnownOne) == (DemandedMask & (~RHSKnownZero))) return I->getOperand(0); if ((DemandedMask & (~LHSKnownZero) & RHSKnownOne) == (DemandedMask & (~LHSKnownZero))) return I->getOperand(1); } // Compute the KnownZero/KnownOne bits to simplify things downstream. ComputeMaskedBits(I, DemandedMask, KnownZero, KnownOne, Depth); return 0; } // If this is the root being simplified, allow it to have multiple uses, // just set the DemandedMask to all bits so that we can try to simplify the // operands. This allows visitTruncInst (for example) to simplify the // operand of a trunc without duplicating all the logic below. if (Depth == 0 && !V->hasOneUse()) DemandedMask = APInt::getAllOnesValue(BitWidth); switch (I->getOpcode()) { default: ComputeMaskedBits(I, DemandedMask, KnownZero, KnownOne, Depth); break; case Instruction::And: // If either the LHS or the RHS are Zero, the result is zero. if (SimplifyDemandedBits(I->getOperandUse(1), DemandedMask, RHSKnownZero, RHSKnownOne, Depth+1) || SimplifyDemandedBits(I->getOperandUse(0), DemandedMask & ~RHSKnownZero, LHSKnownZero, LHSKnownOne, Depth+1)) return I; assert(!(RHSKnownZero & RHSKnownOne) && "Bits known to be one AND zero?"); assert(!(LHSKnownZero & LHSKnownOne) && "Bits known to be one AND zero?"); // If all of the demanded bits are known 1 on one side, return the other. // These bits cannot contribute to the result of the 'and'. if ((DemandedMask & ~LHSKnownZero & RHSKnownOne) == (DemandedMask & ~LHSKnownZero)) return I->getOperand(0); if ((DemandedMask & ~RHSKnownZero & LHSKnownOne) == (DemandedMask & ~RHSKnownZero)) return I->getOperand(1); // If all of the demanded bits in the inputs are known zeros, return zero. if ((DemandedMask & (RHSKnownZero|LHSKnownZero)) == DemandedMask) return Constant::getNullValue(VTy); // If the RHS is a constant, see if we can simplify it. if (ShrinkDemandedConstant(I, 1, DemandedMask & ~LHSKnownZero)) return I; // Output known-1 bits are only known if set in both the LHS & RHS. KnownOne = RHSKnownOne & LHSKnownOne; // Output known-0 are known to be clear if zero in either the LHS | RHS. KnownZero = RHSKnownZero | LHSKnownZero; break; case Instruction::Or: // If either the LHS or the RHS are One, the result is One. if (SimplifyDemandedBits(I->getOperandUse(1), DemandedMask, RHSKnownZero, RHSKnownOne, Depth+1) || SimplifyDemandedBits(I->getOperandUse(0), DemandedMask & ~RHSKnownOne, LHSKnownZero, LHSKnownOne, Depth+1)) return I; assert(!(RHSKnownZero & RHSKnownOne) && "Bits known to be one AND zero?"); assert(!(LHSKnownZero & LHSKnownOne) && "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 & ~LHSKnownOne & RHSKnownZero) == (DemandedMask & ~LHSKnownOne)) return I->getOperand(0); if ((DemandedMask & ~RHSKnownOne & LHSKnownZero) == (DemandedMask & ~RHSKnownOne)) return I->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 & (~RHSKnownZero) & LHSKnownOne) == (DemandedMask & (~RHSKnownZero))) return I->getOperand(0); if ((DemandedMask & (~LHSKnownZero) & RHSKnownOne) == (DemandedMask & (~LHSKnownZero))) return I->getOperand(1); // If the RHS is a constant, see if we can simplify it. if (ShrinkDemandedConstant(I, 1, DemandedMask)) return I; // Output known-0 bits are only known if clear in both the LHS & RHS. KnownZero = RHSKnownZero & LHSKnownZero; // Output known-1 are known to be set if set in either the LHS | RHS. KnownOne = RHSKnownOne | LHSKnownOne; break; case Instruction::Xor: { if (SimplifyDemandedBits(I->getOperandUse(1), DemandedMask, RHSKnownZero, RHSKnownOne, Depth+1) || SimplifyDemandedBits(I->getOperandUse(0), DemandedMask, LHSKnownZero, LHSKnownOne, Depth+1)) return I; assert(!(RHSKnownZero & RHSKnownOne) && "Bits known to be one AND zero?"); assert(!(LHSKnownZero & LHSKnownOne) && "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 & RHSKnownZero) == DemandedMask) return I->getOperand(0); if ((DemandedMask & LHSKnownZero) == DemandedMask) return I->getOperand(1); // If all of the demanded bits are known to be zero on one side or the // other, turn this into an *inclusive* or. // e.g. (A & C1)^(B & C2) -> (A & C1)|(B & C2) iff C1&C2 == 0 if ((DemandedMask & ~RHSKnownZero & ~LHSKnownZero) == 0) { Instruction *Or = BinaryOperator::CreateOr(I->getOperand(0), I->getOperand(1), I->getName()); return InsertNewInstBefore(Or, *I); } // 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 & (RHSKnownZero|RHSKnownOne)) == DemandedMask) { // all known if ((RHSKnownOne & LHSKnownOne) == RHSKnownOne) { Constant *AndC = Constant::getIntegerValue(VTy, ~RHSKnownOne & DemandedMask); Instruction *And = BinaryOperator::CreateAnd(I->getOperand(0), AndC, "tmp"); return InsertNewInstBefore(And, *I); } } // 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 (ShrinkDemandedConstant(I, 1, DemandedMask)) return I; // If our LHS is an 'and' and if it has one use, and if any of the bits we // are flipping are known to be set, then the xor is just resetting those // bits to zero. We can just knock out bits from the 'and' and the 'xor', // simplifying both of them. if (Instruction *LHSInst = dyn_cast(I->getOperand(0))) if (LHSInst->getOpcode() == Instruction::And && LHSInst->hasOneUse() && isa(I->getOperand(1)) && isa(LHSInst->getOperand(1)) && (LHSKnownOne & RHSKnownOne & DemandedMask) != 0) { ConstantInt *AndRHS = cast(LHSInst->getOperand(1)); ConstantInt *XorRHS = cast(I->getOperand(1)); APInt NewMask = ~(LHSKnownOne & RHSKnownOne & DemandedMask); Constant *AndC = ConstantInt::get(I->getType(), NewMask & AndRHS->getValue()); Instruction *NewAnd = BinaryOperator::CreateAnd(I->getOperand(0), AndC, "tmp"); InsertNewInstBefore(NewAnd, *I); Constant *XorC = ConstantInt::get(I->getType(), NewMask & XorRHS->getValue()); Instruction *NewXor = BinaryOperator::CreateXor(NewAnd, XorC, "tmp"); return InsertNewInstBefore(NewXor, *I); } // Output known-0 bits are known if clear or set in both the LHS & RHS. KnownZero= (RHSKnownZero & LHSKnownZero) | (RHSKnownOne & LHSKnownOne); // Output known-1 are known to be set if set in only one of the LHS, RHS. KnownOne = (RHSKnownZero & LHSKnownOne) | (RHSKnownOne & LHSKnownZero); break; } case Instruction::Select: if (SimplifyDemandedBits(I->getOperandUse(2), DemandedMask, RHSKnownZero, RHSKnownOne, Depth+1) || SimplifyDemandedBits(I->getOperandUse(1), DemandedMask, LHSKnownZero, LHSKnownOne, Depth+1)) return I; assert(!(RHSKnownZero & RHSKnownOne) && "Bits known to be one AND zero?"); assert(!(LHSKnownZero & LHSKnownOne) && "Bits known to be one AND zero?"); // If the operands are constants, see if we can simplify them. if (ShrinkDemandedConstant(I, 1, DemandedMask) || ShrinkDemandedConstant(I, 2, DemandedMask)) return I; // Only known if known in both the LHS and RHS. KnownOne = RHSKnownOne & LHSKnownOne; KnownZero = RHSKnownZero & LHSKnownZero; break; case Instruction::Trunc: { unsigned truncBf = I->getOperand(0)->getType()->getScalarSizeInBits(); DemandedMask.zext(truncBf); KnownZero.zext(truncBf); KnownOne.zext(truncBf); if (SimplifyDemandedBits(I->getOperandUse(0), DemandedMask, KnownZero, KnownOne, Depth+1)) return I; DemandedMask.trunc(BitWidth); KnownZero.trunc(BitWidth); KnownOne.trunc(BitWidth); assert(!(KnownZero & KnownOne) && "Bits known to be one AND zero?"); break; } case Instruction::BitCast: if (!I->getOperand(0)->getType()->isIntOrIntVectorTy()) return 0; // vector->int or fp->int? if (const VectorType *DstVTy = dyn_cast(I->getType())) { if (const VectorType *SrcVTy = dyn_cast(I->getOperand(0)->getType())) { if (DstVTy->getNumElements() != SrcVTy->getNumElements()) // Don't touch a bitcast between vectors of different element counts. return 0; } else // Don't touch a scalar-to-vector bitcast. return 0; } else if (I->getOperand(0)->getType()->isVectorTy()) // Don't touch a vector-to-scalar bitcast. return 0; if (SimplifyDemandedBits(I->getOperandUse(0), DemandedMask, KnownZero, KnownOne, Depth+1)) return I; assert(!(KnownZero & KnownOne) && "Bits known to be one AND zero?"); break; case Instruction::ZExt: { // Compute the bits in the result that are not present in the input. unsigned SrcBitWidth =I->getOperand(0)->getType()->getScalarSizeInBits(); DemandedMask.trunc(SrcBitWidth); KnownZero.trunc(SrcBitWidth); KnownOne.trunc(SrcBitWidth); if (SimplifyDemandedBits(I->getOperandUse(0), DemandedMask, KnownZero, KnownOne, Depth+1)) return I; DemandedMask.zext(BitWidth); KnownZero.zext(BitWidth); KnownOne.zext(BitWidth); assert(!(KnownZero & KnownOne) && "Bits known to be one AND zero?"); // The top bits are known to be zero. KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth); break; } case Instruction::SExt: { // Compute the bits in the result that are not present in the input. unsigned SrcBitWidth =I->getOperand(0)->getType()->getScalarSizeInBits(); APInt InputDemandedBits = DemandedMask & APInt::getLowBitsSet(BitWidth, SrcBitWidth); APInt NewBits(APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth)); // If any of the sign extended bits are demanded, we know that the sign // bit is demanded. if ((NewBits & DemandedMask) != 0) InputDemandedBits.set(SrcBitWidth-1); InputDemandedBits.trunc(SrcBitWidth); KnownZero.trunc(SrcBitWidth); KnownOne.trunc(SrcBitWidth); if (SimplifyDemandedBits(I->getOperandUse(0), InputDemandedBits, KnownZero, KnownOne, Depth+1)) return I; InputDemandedBits.zext(BitWidth); KnownZero.zext(BitWidth); KnownOne.zext(BitWidth); assert(!(KnownZero & KnownOne) && "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[SrcBitWidth-1] || (NewBits & ~DemandedMask) == NewBits) { // Convert to ZExt cast CastInst *NewCast = new ZExtInst(I->getOperand(0), VTy, I->getName()); return InsertNewInstBefore(NewCast, *I); } else if (KnownOne[SrcBitWidth-1]) { // Input sign bit known set KnownOne |= NewBits; } break; } case Instruction::Add: { // Figure out what the input bits are. If the top bits of the and result // are not demanded, then the add doesn't demand them from its input // either. unsigned NLZ = DemandedMask.countLeadingZeros(); // If there is a constant on the RHS, there are a variety of xformations // we can do. if (ConstantInt *RHS = dyn_cast(I->getOperand(1))) { // If null, this should be simplified elsewhere. Some of the xforms here // won't work if the RHS is zero. if (RHS->isZero()) break; // If the top bit of the output is demanded, demand everything from the // input. Otherwise, we demand all the input bits except NLZ top bits. APInt InDemandedBits(APInt::getLowBitsSet(BitWidth, BitWidth - NLZ)); // Find information about known zero/one bits in the input. if (SimplifyDemandedBits(I->getOperandUse(0), InDemandedBits, LHSKnownZero, LHSKnownOne, Depth+1)) return I; // If the RHS of the add has bits set that can't affect the input, reduce // the constant. if (ShrinkDemandedConstant(I, 1, InDemandedBits)) return I; // Avoid excess work. if (LHSKnownZero == 0 && LHSKnownOne == 0) break; // Turn it into OR if input bits are zero. if ((LHSKnownZero & RHS->getValue()) == RHS->getValue()) { Instruction *Or = BinaryOperator::CreateOr(I->getOperand(0), I->getOperand(1), I->getName()); return InsertNewInstBefore(Or, *I); } // We can say something about the output known-zero and known-one bits, // depending on potential carries from the input constant and the // unknowns. For example if the LHS is known to have at most the 0x0F0F0 // bits set and the RHS constant is 0x01001, then we know we have a known // one mask of 0x00001 and a known zero mask of 0xE0F0E. // To compute this, we first compute the potential carry bits. These are // the bits which may be modified. I'm not aware of a better way to do // this scan. const APInt &RHSVal = RHS->getValue(); APInt CarryBits((~LHSKnownZero + RHSVal) ^ (~LHSKnownZero ^ RHSVal)); // Now that we know which bits have carries, compute the known-1/0 sets. // Bits are known one if they are known zero in one operand and one in the // other, and there is no input carry. KnownOne = ((LHSKnownZero & RHSVal) | (LHSKnownOne & ~RHSVal)) & ~CarryBits; // Bits are known zero if they are known zero in both operands and there // is no input carry. KnownZero = LHSKnownZero & ~RHSVal & ~CarryBits; } else { // If the high-bits of this ADD are not demanded, then it does not demand // the high bits of its LHS or RHS. if (DemandedMask[BitWidth-1] == 0) { // Right fill the mask of bits for this ADD to demand the most // significant bit and all those below it. APInt DemandedFromOps(APInt::getLowBitsSet(BitWidth, BitWidth-NLZ)); if (SimplifyDemandedBits(I->getOperandUse(0), DemandedFromOps, LHSKnownZero, LHSKnownOne, Depth+1) || SimplifyDemandedBits(I->getOperandUse(1), DemandedFromOps, LHSKnownZero, LHSKnownOne, Depth+1)) return I; } } break; } case Instruction::Sub: // If the high-bits of this SUB are not demanded, then it does not demand // the high bits of its LHS or RHS. if (DemandedMask[BitWidth-1] == 0) { // Right fill the mask of bits for this SUB to demand the most // significant bit and all those below it. uint32_t NLZ = DemandedMask.countLeadingZeros(); APInt DemandedFromOps(APInt::getLowBitsSet(BitWidth, BitWidth-NLZ)); if (SimplifyDemandedBits(I->getOperandUse(0), DemandedFromOps, LHSKnownZero, LHSKnownOne, Depth+1) || SimplifyDemandedBits(I->getOperandUse(1), DemandedFromOps, LHSKnownZero, LHSKnownOne, Depth+1)) return I; } // Otherwise just hand the sub off to ComputeMaskedBits to fill in // the known zeros and ones. ComputeMaskedBits(V, DemandedMask, KnownZero, KnownOne, Depth); break; case Instruction::Shl: if (ConstantInt *SA = dyn_cast(I->getOperand(1))) { uint64_t ShiftAmt = SA->getLimitedValue(BitWidth); APInt DemandedMaskIn(DemandedMask.lshr(ShiftAmt)); if (SimplifyDemandedBits(I->getOperandUse(0), DemandedMaskIn, KnownZero, KnownOne, Depth+1)) return I; assert(!(KnownZero & KnownOne) && "Bits known to be one AND zero?"); KnownZero <<= ShiftAmt; KnownOne <<= ShiftAmt; // low bits known zero. if (ShiftAmt) KnownZero |= APInt::getLowBitsSet(BitWidth, ShiftAmt); } break; case Instruction::LShr: // For a logical shift right if (ConstantInt *SA = dyn_cast(I->getOperand(1))) { uint64_t ShiftAmt = SA->getLimitedValue(BitWidth); // Unsigned shift right. APInt DemandedMaskIn(DemandedMask.shl(ShiftAmt)); if (SimplifyDemandedBits(I->getOperandUse(0), DemandedMaskIn, KnownZero, KnownOne, Depth+1)) return I; assert(!(KnownZero & KnownOne) && "Bits known to be one AND zero?"); KnownZero = APIntOps::lshr(KnownZero, ShiftAmt); KnownOne = APIntOps::lshr(KnownOne, ShiftAmt); if (ShiftAmt) { // Compute the new bits that are at the top now. APInt HighBits(APInt::getHighBitsSet(BitWidth, ShiftAmt)); KnownZero |= HighBits; // high bits known zero. } } break; case Instruction::AShr: // If this is an arithmetic shift right and only the low-bit is set, we can // always convert this into a logical shr, even if the shift amount is // variable. The low bit of the shift cannot be an input sign bit unless // the shift amount is >= the size of the datatype, which is undefined. if (DemandedMask == 1) { // Perform the logical shift right. Instruction *NewVal = BinaryOperator::CreateLShr( I->getOperand(0), I->getOperand(1), I->getName()); return InsertNewInstBefore(NewVal, *I); } // If the sign bit is the only bit demanded by this ashr, then there is no // need to do it, the shift doesn't change the high bit. if (DemandedMask.isSignBit()) return I->getOperand(0); if (ConstantInt *SA = dyn_cast(I->getOperand(1))) { uint32_t ShiftAmt = SA->getLimitedValue(BitWidth); // Signed shift right. APInt DemandedMaskIn(DemandedMask.shl(ShiftAmt)); // If any of the "high bits" are demanded, we should set the sign bit as // demanded. if (DemandedMask.countLeadingZeros() <= ShiftAmt) DemandedMaskIn.set(BitWidth-1); if (SimplifyDemandedBits(I->getOperandUse(0), DemandedMaskIn, KnownZero, KnownOne, Depth+1)) return I; assert(!(KnownZero & KnownOne) && "Bits known to be one AND zero?"); // Compute the new bits that are at the top now. APInt HighBits(APInt::getHighBitsSet(BitWidth, ShiftAmt)); KnownZero = APIntOps::lshr(KnownZero, ShiftAmt); KnownOne = APIntOps::lshr(KnownOne, ShiftAmt); // Handle the sign bits. APInt SignBit(APInt::getSignBit(BitWidth)); // Adjust to where it is now in the mask. SignBit = APIntOps::lshr(SignBit, ShiftAmt); // 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 (BitWidth <= ShiftAmt || KnownZero[BitWidth-ShiftAmt-1] || (HighBits & ~DemandedMask) == HighBits) { // Perform the logical shift right. Instruction *NewVal = BinaryOperator::CreateLShr( I->getOperand(0), SA, I->getName()); return InsertNewInstBefore(NewVal, *I); } else if ((KnownOne & SignBit) != 0) { // New bits are known one. KnownOne |= HighBits; } } break; case Instruction::SRem: if (ConstantInt *Rem = dyn_cast(I->getOperand(1))) { APInt RA = Rem->getValue().abs(); if (RA.isPowerOf2()) { if (DemandedMask.ult(RA)) // srem won't affect demanded bits return I->getOperand(0); APInt LowBits = RA - 1; APInt Mask2 = LowBits | APInt::getSignBit(BitWidth); if (SimplifyDemandedBits(I->getOperandUse(0), Mask2, LHSKnownZero, LHSKnownOne, Depth+1)) return I; // The low bits of LHS are unchanged by the srem. KnownZero = LHSKnownZero & LowBits; KnownOne = LHSKnownOne & LowBits; // If LHS is non-negative or has all low bits zero, then the upper bits // are all zero. if (LHSKnownZero[BitWidth-1] || ((LHSKnownZero & LowBits) == LowBits)) KnownZero |= ~LowBits; // If LHS is negative and not all low bits are zero, then the upper bits // are all one. if (LHSKnownOne[BitWidth-1] && ((LHSKnownOne & LowBits) != 0)) KnownOne |= ~LowBits; assert(!(KnownZero & KnownOne) && "Bits known to be one AND zero?"); } } break; case Instruction::URem: { APInt KnownZero2(BitWidth, 0), KnownOne2(BitWidth, 0); APInt AllOnes = APInt::getAllOnesValue(BitWidth); if (SimplifyDemandedBits(I->getOperandUse(0), AllOnes, KnownZero2, KnownOne2, Depth+1) || SimplifyDemandedBits(I->getOperandUse(1), AllOnes, KnownZero2, KnownOne2, Depth+1)) return I; unsigned Leaders = KnownZero2.countLeadingOnes(); Leaders = std::max(Leaders, KnownZero2.countLeadingOnes()); KnownZero = APInt::getHighBitsSet(BitWidth, Leaders) & DemandedMask; break; } case Instruction::Call: if (IntrinsicInst *II = dyn_cast(I)) { switch (II->getIntrinsicID()) { default: break; case Intrinsic::bswap: { // If the only bits demanded come from one byte of the bswap result, // just shift the input byte into position to eliminate the bswap. unsigned NLZ = DemandedMask.countLeadingZeros(); unsigned NTZ = DemandedMask.countTrailingZeros(); // Round NTZ down to the next byte. If we have 11 trailing zeros, then // we need all the bits down to bit 8. Likewise, round NLZ. If we // have 14 leading zeros, round to 8. NLZ &= ~7; NTZ &= ~7; // If we need exactly one byte, we can do this transformation. if (BitWidth-NLZ-NTZ == 8) { unsigned ResultBit = NTZ; unsigned InputBit = BitWidth-NTZ-8; // Replace this with either a left or right shift to get the byte into // the right place. Instruction *NewVal; if (InputBit > ResultBit) NewVal = BinaryOperator::CreateLShr(I->getOperand(1), ConstantInt::get(I->getType(), InputBit-ResultBit)); else NewVal = BinaryOperator::CreateShl(I->getOperand(1), ConstantInt::get(I->getType(), ResultBit-InputBit)); NewVal->takeName(I); return InsertNewInstBefore(NewVal, *I); } // TODO: Could compute known zero/one bits based on the input. break; } } } ComputeMaskedBits(V, DemandedMask, KnownZero, KnownOne, Depth); break; } // If the client is only demanding bits that we know, return the known // constant. if ((DemandedMask & (KnownZero|KnownOne)) == DemandedMask) return Constant::getIntegerValue(VTy, KnownOne); return 0; } /// SimplifyDemandedVectorElts - The specified value produces a vector with /// any number of elements. DemandedElts contains the set of elements that are /// actually used by the caller. This method analyzes which elements of the /// operand are undef and returns that information in UndefElts. /// /// If the information about demanded elements can be used to simplify the /// operation, the operation is simplified, then the resultant value is /// returned. This returns null if no change was made. Value *InstCombiner::SimplifyDemandedVectorElts(Value *V, APInt DemandedElts, APInt &UndefElts, unsigned Depth) { unsigned VWidth = cast(V->getType())->getNumElements(); APInt EltMask(APInt::getAllOnesValue(VWidth)); assert((DemandedElts & ~EltMask) == 0 && "Invalid DemandedElts!"); if (isa(V)) { // If the entire vector is undefined, just return this info. UndefElts = EltMask; return 0; } if (DemandedElts == 0) { // If nothing is demanded, provide undef. UndefElts = EltMask; return UndefValue::get(V->getType()); } UndefElts = 0; if (ConstantVector *CV = dyn_cast(V)) { const Type *EltTy = cast(V->getType())->getElementType(); Constant *Undef = UndefValue::get(EltTy); std::vector Elts; for (unsigned i = 0; i != VWidth; ++i) if (!DemandedElts[i]) { // If not demanded, set to undef. Elts.push_back(Undef); UndefElts.set(i); } else if (isa(CV->getOperand(i))) { // Already undef. Elts.push_back(Undef); UndefElts.set(i); } else { // Otherwise, defined. Elts.push_back(CV->getOperand(i)); } // If we changed the constant, return it. Constant *NewCP = ConstantVector::get(Elts); return NewCP != CV ? NewCP : 0; } if (isa(V)) { // Simplify the CAZ to a ConstantVector where the non-demanded elements are // set to undef. // Check if this is identity. If so, return 0 since we are not simplifying // anything. if (DemandedElts.isAllOnesValue()) return 0; const Type *EltTy = cast(V->getType())->getElementType(); Constant *Zero = Constant::getNullValue(EltTy); Constant *Undef = UndefValue::get(EltTy); std::vector Elts; for (unsigned i = 0; i != VWidth; ++i) { Constant *Elt = DemandedElts[i] ? Zero : Undef; Elts.push_back(Elt); } UndefElts = DemandedElts ^ EltMask; return ConstantVector::get(Elts); } // Limit search depth. if (Depth == 10) return 0; // If multiple users are using the root value, procede with // simplification conservatively assuming that all elements // are needed. if (!V->hasOneUse()) { // Quit if we find multiple users of a non-root value though. // They'll be handled when it's their turn to be visited by // the main instcombine process. if (Depth != 0) // TODO: Just compute the UndefElts information recursively. return 0; // Conservatively assume that all elements are needed. DemandedElts = EltMask; } Instruction *I = dyn_cast(V); if (!I) return 0; // Only analyze instructions. bool MadeChange = false; APInt UndefElts2(VWidth, 0); Value *TmpV; switch (I->getOpcode()) { default: break; case Instruction::InsertElement: { // If this is a variable index, we don't know which element it overwrites. // demand exactly the same input as we produce. ConstantInt *Idx = dyn_cast(I->getOperand(2)); if (Idx == 0) { // Note that we can't propagate undef elt info, because we don't know // which elt is getting updated. TmpV = SimplifyDemandedVectorElts(I->getOperand(0), DemandedElts, UndefElts2, Depth+1); if (TmpV) { I->setOperand(0, TmpV); MadeChange = true; } break; } // If this is inserting an element that isn't demanded, remove this // insertelement. unsigned IdxNo = Idx->getZExtValue(); if (IdxNo >= VWidth || !DemandedElts[IdxNo]) { Worklist.Add(I); return I->getOperand(0); } // Otherwise, the element inserted overwrites whatever was there, so the // input demanded set is simpler than the output set. APInt DemandedElts2 = DemandedElts; DemandedElts2.clear(IdxNo); TmpV = SimplifyDemandedVectorElts(I->getOperand(0), DemandedElts2, UndefElts, Depth+1); if (TmpV) { I->setOperand(0, TmpV); MadeChange = true; } // The inserted element is defined. UndefElts.clear(IdxNo); break; } case Instruction::ShuffleVector: { ShuffleVectorInst *Shuffle = cast(I); uint64_t LHSVWidth = cast(Shuffle->getOperand(0)->getType())->getNumElements(); APInt LeftDemanded(LHSVWidth, 0), RightDemanded(LHSVWidth, 0); for (unsigned i = 0; i < VWidth; i++) { if (DemandedElts[i]) { unsigned MaskVal = Shuffle->getMaskValue(i); if (MaskVal != -1u) { assert(MaskVal < LHSVWidth * 2 && "shufflevector mask index out of range!"); if (MaskVal < LHSVWidth) LeftDemanded.set(MaskVal); else RightDemanded.set(MaskVal - LHSVWidth); } } } APInt UndefElts4(LHSVWidth, 0); TmpV = SimplifyDemandedVectorElts(I->getOperand(0), LeftDemanded, UndefElts4, Depth+1); if (TmpV) { I->setOperand(0, TmpV); MadeChange = true; } APInt UndefElts3(LHSVWidth, 0); TmpV = SimplifyDemandedVectorElts(I->getOperand(1), RightDemanded, UndefElts3, Depth+1); if (TmpV) { I->setOperand(1, TmpV); MadeChange = true; } bool NewUndefElts = false; for (unsigned i = 0; i < VWidth; i++) { unsigned MaskVal = Shuffle->getMaskValue(i); if (MaskVal == -1u) { UndefElts.set(i); } else if (MaskVal < LHSVWidth) { if (UndefElts4[MaskVal]) { NewUndefElts = true; UndefElts.set(i); } } else { if (UndefElts3[MaskVal - LHSVWidth]) { NewUndefElts = true; UndefElts.set(i); } } } if (NewUndefElts) { // Add additional discovered undefs. std::vector Elts; for (unsigned i = 0; i < VWidth; ++i) { if (UndefElts[i]) Elts.push_back(UndefValue::get(Type::getInt32Ty(I->getContext()))); else Elts.push_back(ConstantInt::get(Type::getInt32Ty(I->getContext()), Shuffle->getMaskValue(i))); } I->setOperand(2, ConstantVector::get(Elts)); MadeChange = true; } break; } case Instruction::BitCast: { // Vector->vector casts only. const VectorType *VTy = dyn_cast(I->getOperand(0)->getType()); if (!VTy) break; unsigned InVWidth = VTy->getNumElements(); APInt InputDemandedElts(InVWidth, 0); unsigned Ratio; if (VWidth == InVWidth) { // If we are converting from <4 x i32> -> <4 x f32>, we demand the same // elements as are demanded of us. Ratio = 1; InputDemandedElts = DemandedElts; } else if (VWidth > InVWidth) { // Untested so far. break; // If there are more elements in the result than there are in the source, // then an input element is live if any of the corresponding output // elements are live. Ratio = VWidth/InVWidth; for (unsigned OutIdx = 0; OutIdx != VWidth; ++OutIdx) { if (DemandedElts[OutIdx]) InputDemandedElts.set(OutIdx/Ratio); } } else { // Untested so far. break; // If there are more elements in the source than there are in the result, // then an input element is live if the corresponding output element is // live. Ratio = InVWidth/VWidth; for (unsigned InIdx = 0; InIdx != InVWidth; ++InIdx) if (DemandedElts[InIdx/Ratio]) InputDemandedElts.set(InIdx); } // div/rem demand all inputs, because they don't want divide by zero. TmpV = SimplifyDemandedVectorElts(I->getOperand(0), InputDemandedElts, UndefElts2, Depth+1); if (TmpV) { I->setOperand(0, TmpV); MadeChange = true; } UndefElts = UndefElts2; if (VWidth > InVWidth) { llvm_unreachable("Unimp"); // If there are more elements in the result than there are in the source, // then an output element is undef if the corresponding input element is // undef. for (unsigned OutIdx = 0; OutIdx != VWidth; ++OutIdx) if (UndefElts2[OutIdx/Ratio]) UndefElts.set(OutIdx); } else if (VWidth < InVWidth) { llvm_unreachable("Unimp"); // If there are more elements in the source than there are in the result, // then a result element is undef if all of the corresponding input // elements are undef. UndefElts = ~0ULL >> (64-VWidth); // Start out all undef. for (unsigned InIdx = 0; InIdx != InVWidth; ++InIdx) if (!UndefElts2[InIdx]) // Not undef? UndefElts.clear(InIdx/Ratio); // Clear undef bit. } break; } case Instruction::And: case Instruction::Or: case Instruction::Xor: case Instruction::Add: case Instruction::Sub: case Instruction::Mul: // div/rem demand all inputs, because they don't want divide by zero. TmpV = SimplifyDemandedVectorElts(I->getOperand(0), DemandedElts, UndefElts, Depth+1); if (TmpV) { I->setOperand(0, TmpV); MadeChange = true; } TmpV = SimplifyDemandedVectorElts(I->getOperand(1), DemandedElts, UndefElts2, Depth+1); if (TmpV) { I->setOperand(1, TmpV); MadeChange = true; } // Output elements are undefined if both are undefined. Consider things // like undef&0. The result is known zero, not undef. UndefElts &= UndefElts2; break; case Instruction::Call: { IntrinsicInst *II = dyn_cast(I); if (!II) break; switch (II->getIntrinsicID()) { default: break; // Binary vector operations that work column-wise. A dest element is a // function of the corresponding input elements from the two inputs. case Intrinsic::x86_sse_sub_ss: case Intrinsic::x86_sse_mul_ss: case Intrinsic::x86_sse_min_ss: case Intrinsic::x86_sse_max_ss: case Intrinsic::x86_sse2_sub_sd: case Intrinsic::x86_sse2_mul_sd: case Intrinsic::x86_sse2_min_sd: case Intrinsic::x86_sse2_max_sd: TmpV = SimplifyDemandedVectorElts(II->getOperand(1), DemandedElts, UndefElts, Depth+1); if (TmpV) { II->setOperand(1, TmpV); MadeChange = true; } TmpV = SimplifyDemandedVectorElts(II->getOperand(2), DemandedElts, UndefElts2, Depth+1); if (TmpV) { II->setOperand(2, TmpV); MadeChange = true; } // If only the low elt is demanded and this is a scalarizable intrinsic, // scalarize it now. if (DemandedElts == 1) { switch (II->getIntrinsicID()) { default: break; case Intrinsic::x86_sse_sub_ss: case Intrinsic::x86_sse_mul_ss: case Intrinsic::x86_sse2_sub_sd: case Intrinsic::x86_sse2_mul_sd: // TODO: Lower MIN/MAX/ABS/etc Value *LHS = II->getOperand(1); Value *RHS = II->getOperand(2); // Extract the element as scalars. LHS = InsertNewInstBefore(ExtractElementInst::Create(LHS, ConstantInt::get(Type::getInt32Ty(I->getContext()), 0U)), *II); RHS = InsertNewInstBefore(ExtractElementInst::Create(RHS, ConstantInt::get(Type::getInt32Ty(I->getContext()), 0U)), *II); switch (II->getIntrinsicID()) { default: llvm_unreachable("Case stmts out of sync!"); case Intrinsic::x86_sse_sub_ss: case Intrinsic::x86_sse2_sub_sd: TmpV = InsertNewInstBefore(BinaryOperator::CreateFSub(LHS, RHS, II->getName()), *II); break; case Intrinsic::x86_sse_mul_ss: case Intrinsic::x86_sse2_mul_sd: TmpV = InsertNewInstBefore(BinaryOperator::CreateFMul(LHS, RHS, II->getName()), *II); break; } Instruction *New = InsertElementInst::Create( UndefValue::get(II->getType()), TmpV, ConstantInt::get(Type::getInt32Ty(I->getContext()), 0U, false), II->getName()); InsertNewInstBefore(New, *II); return New; } } // Output elements are undefined if both are undefined. Consider things // like undef&0. The result is known zero, not undef. UndefElts &= UndefElts2; break; } break; } } return MadeChange ? I : 0; }