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//===- 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 "InstCombineInternal.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/PatternMatch.h"
using namespace llvm;
using namespace llvm::PatternMatch;
#define DEBUG_TYPE "instcombine"
/// 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<ConstantInt>(I->getOperand(OpNo));
if (!OpC) return false;
// If there are no bits set that aren't demanded, nothing to do.
Demanded = 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;
}
/// 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, &Inst);
if (!V) return false;
if (V == &Inst) return true;
replaceInstUsesWith(Inst, V);
return true;
}
/// 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, const APInt &DemandedMask,
APInt &KnownZero, APInt &KnownOne,
unsigned Depth) {
auto *UserI = dyn_cast<Instruction>(U.getUser());
Value *NewVal = SimplifyDemandedUseBits(U.get(), DemandedMask, KnownZero,
KnownOne, Depth, UserI);
if (!NewVal) return false;
U = NewVal;
return true;
}
/// 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,
Instruction *CxtI) {
assert(V != nullptr && "Null pointer of Value???");
assert(Depth <= 6 && "Limit Search Depth");
uint32_t BitWidth = DemandedMask.getBitWidth();
Type *VTy = V->getType();
assert(
(!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<ConstantInt>(V)) {
// We know all of the bits for a constant!
KnownOne = CI->getValue() & DemandedMask;
KnownZero = ~KnownOne & DemandedMask;
return nullptr;
}
if (isa<ConstantPointerNull>(V)) {
// We know all of the bits for a constant!
KnownOne.clearAllBits();
KnownZero = DemandedMask;
return nullptr;
}
KnownZero.clearAllBits();
KnownOne.clearAllBits();
if (DemandedMask == 0) { // Not demanding any bits from V.
if (isa<UndefValue>(V))
return nullptr;
return UndefValue::get(VTy);
}
if (Depth == 6) // Limit search depth.
return nullptr;
APInt LHSKnownZero(BitWidth, 0), LHSKnownOne(BitWidth, 0);
APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
Instruction *I = dyn_cast<Instruction>(V);
if (!I) {
computeKnownBits(V, KnownZero, KnownOne, Depth, CxtI);
return nullptr; // 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.
computeKnownBits(I->getOperand(1), RHSKnownZero, RHSKnownOne, Depth + 1,
CxtI);
computeKnownBits(I->getOperand(0), LHSKnownZero, LHSKnownOne, Depth + 1,
CxtI);
// 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.
computeKnownBits(I->getOperand(1), RHSKnownZero, RHSKnownOne, Depth + 1,
CxtI);
computeKnownBits(I->getOperand(0), LHSKnownZero, LHSKnownOne, Depth + 1,
CxtI);
// 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);
} else if (I->getOpcode() == Instruction::Xor) {
// 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.
computeKnownBits(I->getOperand(1), RHSKnownZero, RHSKnownOne, Depth + 1,
CxtI);
computeKnownBits(I->getOperand(0), LHSKnownZero, LHSKnownOne, Depth + 1,
CxtI);
// If all of the demanded bits are known zero on one side, return the
// other.
if ((DemandedMask & RHSKnownZero) == DemandedMask)
return I->getOperand(0);
if ((DemandedMask & LHSKnownZero) == DemandedMask)
return I->getOperand(1);
}
// Compute the KnownZero/KnownOne bits to simplify things downstream.
computeKnownBits(I, KnownZero, KnownOne, Depth, CxtI);
return nullptr;
}
// 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:
computeKnownBits(I, KnownZero, KnownOne, Depth, CxtI);
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 the client is only demanding bits that we know, return the known
// constant.
if ((DemandedMask & ((RHSKnownZero | LHSKnownZero)|
(RHSKnownOne & LHSKnownOne))) == DemandedMask)
return Constant::getIntegerValue(VTy, RHSKnownOne & LHSKnownOne);
// 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 the client is only demanding bits that we know, return the known
// constant.
if ((DemandedMask & ((RHSKnownZero & LHSKnownZero)|
(RHSKnownOne | LHSKnownOne))) == DemandedMask)
return Constant::getIntegerValue(VTy, RHSKnownOne | LHSKnownOne);
// 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?");
// Output known-0 bits are known if clear or set in both the LHS & RHS.
APInt IKnownZero = (RHSKnownZero & LHSKnownZero) |
(RHSKnownOne & LHSKnownOne);
// Output known-1 are known to be set if set in only one of the LHS, RHS.
APInt IKnownOne = (RHSKnownZero & LHSKnownOne) |
(RHSKnownOne & LHSKnownZero);
// If the client is only demanding bits that we know, return the known
// constant.
if ((DemandedMask & (IKnownZero|IKnownOne)) == DemandedMask)
return Constant::getIntegerValue(VTy, IKnownOne);
// 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 InsertNewInstWith(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);
return InsertNewInstWith(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<Instruction>(I->getOperand(0)))
if (LHSInst->getOpcode() == Instruction::And && LHSInst->hasOneUse() &&
isa<ConstantInt>(I->getOperand(1)) &&
isa<ConstantInt>(LHSInst->getOperand(1)) &&
(LHSKnownOne & RHSKnownOne & DemandedMask) != 0) {
ConstantInt *AndRHS = cast<ConstantInt>(LHSInst->getOperand(1));
ConstantInt *XorRHS = cast<ConstantInt>(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);
InsertNewInstWith(NewAnd, *I);
Constant *XorC =
ConstantInt::get(I->getType(), NewMask & XorRHS->getValue());
Instruction *NewXor = BinaryOperator::CreateXor(NewAnd, XorC);
return InsertNewInstWith(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 this is a select as part of a min/max pattern, don't simplify any
// further in case we break the structure.
Value *LHS, *RHS;
if (matchSelectPattern(I, LHS, RHS).Flavor != SPF_UNKNOWN)
return nullptr;
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 = DemandedMask.zext(truncBf);
KnownZero = KnownZero.zext(truncBf);
KnownOne = KnownOne.zext(truncBf);
if (SimplifyDemandedBits(I->getOperandUse(0), DemandedMask, KnownZero,
KnownOne, Depth + 1))
return I;
DemandedMask = DemandedMask.trunc(BitWidth);
KnownZero = KnownZero.trunc(BitWidth);
KnownOne = KnownOne.trunc(BitWidth);
assert(!(KnownZero & KnownOne) && "Bits known to be one AND zero?");
break;
}
case Instruction::BitCast:
if (!I->getOperand(0)->getType()->isIntOrIntVectorTy())
return nullptr; // vector->int or fp->int?
if (VectorType *DstVTy = dyn_cast<VectorType>(I->getType())) {
if (VectorType *SrcVTy =
dyn_cast<VectorType>(I->getOperand(0)->getType())) {
if (DstVTy->getNumElements() != SrcVTy->getNumElements())
// Don't touch a bitcast between vectors of different element counts.
return nullptr;
} else
// Don't touch a scalar-to-vector bitcast.
return nullptr;
} else if (I->getOperand(0)->getType()->isVectorTy())
// Don't touch a vector-to-scalar bitcast.
return nullptr;
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 = DemandedMask.trunc(SrcBitWidth);
KnownZero = KnownZero.trunc(SrcBitWidth);
KnownOne = KnownOne.trunc(SrcBitWidth);
if (SimplifyDemandedBits(I->getOperandUse(0), DemandedMask, KnownZero,
KnownOne, Depth + 1))
return I;
DemandedMask = DemandedMask.zext(BitWidth);
KnownZero = KnownZero.zext(BitWidth);
KnownOne = 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.setBit(SrcBitWidth-1);
InputDemandedBits = InputDemandedBits.trunc(SrcBitWidth);
KnownZero = KnownZero.trunc(SrcBitWidth);
KnownOne = KnownOne.trunc(SrcBitWidth);
if (SimplifyDemandedBits(I->getOperandUse(0), InputDemandedBits, KnownZero,
KnownOne, Depth + 1))
return I;
InputDemandedBits = InputDemandedBits.zext(BitWidth);
KnownZero = KnownZero.zext(BitWidth);
KnownOne = 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 InsertNewInstWith(NewCast, *I);
} else if (KnownOne[SrcBitWidth-1]) { // Input sign bit known set
KnownOne |= NewBits;
}
break;
}
case Instruction::Add:
case Instruction::Sub: {
/// If the high-bits of an ADD/SUB are not demanded, then we do not care
/// about the high bits of the operands.
unsigned NLZ = DemandedMask.countLeadingZeros();
if (NLZ > 0) {
// Right fill the mask of bits for this ADD/SUB 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) ||
ShrinkDemandedConstant(I, 1, DemandedFromOps) ||
SimplifyDemandedBits(I->getOperandUse(1), DemandedFromOps,
LHSKnownZero, LHSKnownOne, Depth + 1)) {
// Disable the nsw and nuw flags here: We can no longer guarantee that
// we won't wrap after simplification. Removing the nsw/nuw flags is
// legal here because the top bit is not demanded.
BinaryOperator &BinOP = *cast<BinaryOperator>(I);
BinOP.setHasNoSignedWrap(false);
BinOP.setHasNoUnsignedWrap(false);
return I;
}
}
// Otherwise just hand the add/sub off to computeKnownBits to fill in
// the known zeros and ones.
computeKnownBits(V, KnownZero, KnownOne, Depth, CxtI);
break;
}
case Instruction::Shl:
if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) {
{
Value *VarX; ConstantInt *C1;
if (match(I->getOperand(0), m_Shr(m_Value(VarX), m_ConstantInt(C1)))) {
Instruction *Shr = cast<Instruction>(I->getOperand(0));
Value *R = SimplifyShrShlDemandedBits(Shr, I, DemandedMask,
KnownZero, KnownOne);
if (R)
return R;
}
}
uint64_t ShiftAmt = SA->getLimitedValue(BitWidth-1);
APInt DemandedMaskIn(DemandedMask.lshr(ShiftAmt));
// If the shift is NUW/NSW, then it does demand the high bits.
ShlOperator *IOp = cast<ShlOperator>(I);
if (IOp->hasNoSignedWrap())
DemandedMaskIn |= APInt::getHighBitsSet(BitWidth, ShiftAmt+1);
else if (IOp->hasNoUnsignedWrap())
DemandedMaskIn |= APInt::getHighBitsSet(BitWidth, 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<ConstantInt>(I->getOperand(1))) {
uint64_t ShiftAmt = SA->getLimitedValue(BitWidth-1);
// Unsigned shift right.
APInt DemandedMaskIn(DemandedMask.shl(ShiftAmt));
// If the shift is exact, then it does demand the low bits (and knows that
// they are zero).
if (cast<LShrOperator>(I)->isExact())
DemandedMaskIn |= APInt::getLowBitsSet(BitWidth, 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 InsertNewInstWith(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<ConstantInt>(I->getOperand(1))) {
uint32_t ShiftAmt = SA->getLimitedValue(BitWidth-1);
// 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.setBit(BitWidth-1);
// If the shift is exact, then it does demand the low bits (and knows that
// they are zero).
if (cast<AShrOperator>(I)->isExact())
DemandedMaskIn |= APInt::getLowBitsSet(BitWidth, ShiftAmt);
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.
BinaryOperator *NewVal = BinaryOperator::CreateLShr(I->getOperand(0),
SA, I->getName());
NewVal->setIsExact(cast<BinaryOperator>(I)->isExact());
return InsertNewInstWith(NewVal, *I);
} else if ((KnownOne & SignBit) != 0) { // New bits are known one.
KnownOne |= HighBits;
}
}
break;
case Instruction::SRem:
if (ConstantInt *Rem = dyn_cast<ConstantInt>(I->getOperand(1))) {
// X % -1 demands all the bits because we don't want to introduce
// INT_MIN % -1 (== undef) by accident.
if (Rem->isAllOnesValue())
break;
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?");
}
}
// The sign bit is the LHS's sign bit, except when the result of the
// remainder is zero.
if (DemandedMask.isNegative() && KnownZero.isNonNegative()) {
APInt LHSKnownZero(BitWidth, 0), LHSKnownOne(BitWidth, 0);
computeKnownBits(I->getOperand(0), LHSKnownZero, LHSKnownOne, Depth + 1,
CxtI);
// If it's known zero, our sign bit is also zero.
if (LHSKnownZero.isNegative())
KnownZero.setBit(KnownZero.getBitWidth() - 1);
}
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<IntrinsicInst>(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(II->getArgOperand(0),
ConstantInt::get(I->getType(), InputBit-ResultBit));
else
NewVal = BinaryOperator::CreateShl(II->getArgOperand(0),
ConstantInt::get(I->getType(), ResultBit-InputBit));
NewVal->takeName(I);
return InsertNewInstWith(NewVal, *I);
}
// TODO: Could compute known zero/one bits based on the input.
break;
}
case Intrinsic::x86_mmx_pmovmskb:
case Intrinsic::x86_sse_movmsk_ps:
case Intrinsic::x86_sse2_movmsk_pd:
case Intrinsic::x86_sse2_pmovmskb_128:
case Intrinsic::x86_avx_movmsk_ps_256:
case Intrinsic::x86_avx_movmsk_pd_256:
case Intrinsic::x86_avx2_pmovmskb: {
// MOVMSK copies the vector elements' sign bits to the low bits
// and zeros the high bits.
unsigned ArgWidth;
if (II->getIntrinsicID() == Intrinsic::x86_mmx_pmovmskb) {
ArgWidth = 8; // Arg is x86_mmx, but treated as <8 x i8>.
} else {
auto Arg = II->getArgOperand(0);
auto ArgType = cast<VectorType>(Arg->getType());
ArgWidth = ArgType->getNumElements();
}
// If we don't need any of low bits then return zero,
// we know that DemandedMask is non-zero already.
APInt DemandedElts = DemandedMask.zextOrTrunc(ArgWidth);
if (DemandedElts == 0)
return ConstantInt::getNullValue(VTy);
// We know that the upper bits are set to zero.
KnownZero = APInt::getHighBitsSet(BitWidth, BitWidth - ArgWidth);
return nullptr;
}
case Intrinsic::x86_sse42_crc32_64_64:
KnownZero = APInt::getHighBitsSet(64, 32);
return nullptr;
}
}
computeKnownBits(V, KnownZero, KnownOne, Depth, CxtI);
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 nullptr;
}
/// Helper routine of SimplifyDemandedUseBits. It tries to simplify
/// "E1 = (X lsr C1) << C2", where the C1 and C2 are constant, into
/// "E2 = X << (C2 - C1)" or "E2 = X >> (C1 - C2)", depending on the sign
/// of "C2-C1".
///
/// Suppose E1 and E2 are generally different in bits S={bm, bm+1,
/// ..., bn}, without considering the specific value X is holding.
/// This transformation is legal iff one of following conditions is hold:
/// 1) All the bit in S are 0, in this case E1 == E2.
/// 2) We don't care those bits in S, per the input DemandedMask.
/// 3) Combination of 1) and 2). Some bits in S are 0, and we don't care the
/// rest bits.
///
/// Currently we only test condition 2).
///
/// As with SimplifyDemandedUseBits, it returns NULL if the simplification was
/// not successful.
Value *InstCombiner::SimplifyShrShlDemandedBits(Instruction *Shr,
Instruction *Shl,
const APInt &DemandedMask,
APInt &KnownZero,
APInt &KnownOne) {
const APInt &ShlOp1 = cast<ConstantInt>(Shl->getOperand(1))->getValue();
const APInt &ShrOp1 = cast<ConstantInt>(Shr->getOperand(1))->getValue();
if (!ShlOp1 || !ShrOp1)
return nullptr; // Noop.
Value *VarX = Shr->getOperand(0);
Type *Ty = VarX->getType();
unsigned BitWidth = Ty->getIntegerBitWidth();
if (ShlOp1.uge(BitWidth) || ShrOp1.uge(BitWidth))
return nullptr; // Undef.
unsigned ShlAmt = ShlOp1.getZExtValue();
unsigned ShrAmt = ShrOp1.getZExtValue();
KnownOne.clearAllBits();
KnownZero = APInt::getBitsSet(KnownZero.getBitWidth(), 0, ShlAmt-1);
KnownZero &= DemandedMask;
APInt BitMask1(APInt::getAllOnesValue(BitWidth));
APInt BitMask2(APInt::getAllOnesValue(BitWidth));
bool isLshr = (Shr->getOpcode() == Instruction::LShr);
BitMask1 = isLshr ? (BitMask1.lshr(ShrAmt) << ShlAmt) :
(BitMask1.ashr(ShrAmt) << ShlAmt);
if (ShrAmt <= ShlAmt) {
BitMask2 <<= (ShlAmt - ShrAmt);
} else {
BitMask2 = isLshr ? BitMask2.lshr(ShrAmt - ShlAmt):
BitMask2.ashr(ShrAmt - ShlAmt);
}
// Check if condition-2 (see the comment to this function) is satified.
if ((BitMask1 & DemandedMask) == (BitMask2 & DemandedMask)) {
if (ShrAmt == ShlAmt)
return VarX;
if (!Shr->hasOneUse())
return nullptr;
BinaryOperator *New;
if (ShrAmt < ShlAmt) {
Constant *Amt = ConstantInt::get(VarX->getType(), ShlAmt - ShrAmt);
New = BinaryOperator::CreateShl(VarX, Amt);
BinaryOperator *Orig = cast<BinaryOperator>(Shl);
New->setHasNoSignedWrap(Orig->hasNoSignedWrap());
New->setHasNoUnsignedWrap(Orig->hasNoUnsignedWrap());
} else {
Constant *Amt = ConstantInt::get(VarX->getType(), ShrAmt - ShlAmt);
New = isLshr ? BinaryOperator::CreateLShr(VarX, Amt) :
BinaryOperator::CreateAShr(VarX, Amt);
if (cast<BinaryOperator>(Shr)->isExact())
New->setIsExact(true);
}
return InsertNewInstWith(New, *Shl);
}
return nullptr;
}
/// 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 = V->getType()->getVectorNumElements();
APInt EltMask(APInt::getAllOnesValue(VWidth));
assert((DemandedElts & ~EltMask) == 0 && "Invalid DemandedElts!");
if (isa<UndefValue>(V)) {
// If the entire vector is undefined, just return this info.
UndefElts = EltMask;
return nullptr;
}
if (DemandedElts == 0) { // If nothing is demanded, provide undef.
UndefElts = EltMask;
return UndefValue::get(V->getType());
}
UndefElts = 0;
// Handle ConstantAggregateZero, ConstantVector, ConstantDataSequential.
if (Constant *C = dyn_cast<Constant>(V)) {
// Check if this is identity. If so, return 0 since we are not simplifying
// anything.
if (DemandedElts.isAllOnesValue())
return nullptr;
Type *EltTy = cast<VectorType>(V->getType())->getElementType();
Constant *Undef = UndefValue::get(EltTy);
SmallVector<Constant*, 16> Elts;
for (unsigned i = 0; i != VWidth; ++i) {
if (!DemandedElts[i]) { // If not demanded, set to undef.
Elts.push_back(Undef);
UndefElts.setBit(i);
continue;
}
Constant *Elt = C->getAggregateElement(i);
if (!Elt) return nullptr;
if (isa<UndefValue>(Elt)) { // Already undef.
Elts.push_back(Undef);
UndefElts.setBit(i);
} else { // Otherwise, defined.
Elts.push_back(Elt);
}
}
// If we changed the constant, return it.
Constant *NewCV = ConstantVector::get(Elts);
return NewCV != C ? NewCV : nullptr;
}
// Limit search depth.
if (Depth == 10)
return nullptr;
// If multiple users are using the root value, proceed 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 nullptr;
// Conservatively assume that all elements are needed.
DemandedElts = EltMask;
}
Instruction *I = dyn_cast<Instruction>(V);
if (!I) return nullptr; // Only analyze instructions.
bool MadeChange = false;
APInt UndefElts2(VWidth, 0);
APInt UndefElts3(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<ConstantInt>(I->getOperand(2));
if (!Idx) {
// 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.clearBit(IdxNo);
TmpV = SimplifyDemandedVectorElts(I->getOperand(0), DemandedElts2,
UndefElts, Depth + 1);
if (TmpV) { I->setOperand(0, TmpV); MadeChange = true; }
// The inserted element is defined.
UndefElts.clearBit(IdxNo);
break;
}
case Instruction::ShuffleVector: {
ShuffleVectorInst *Shuffle = cast<ShuffleVectorInst>(I);
unsigned LHSVWidth =
Shuffle->getOperand(0)->getType()->getVectorNumElements();
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.setBit(MaskVal);
else
RightDemanded.setBit(MaskVal - LHSVWidth);
}
}
}
APInt LHSUndefElts(LHSVWidth, 0);
TmpV = SimplifyDemandedVectorElts(I->getOperand(0), LeftDemanded,
LHSUndefElts, Depth + 1);
if (TmpV) { I->setOperand(0, TmpV); MadeChange = true; }
APInt RHSUndefElts(LHSVWidth, 0);
TmpV = SimplifyDemandedVectorElts(I->getOperand(1), RightDemanded,
RHSUndefElts, Depth + 1);
if (TmpV) { I->setOperand(1, TmpV); MadeChange = true; }
bool NewUndefElts = false;
unsigned LHSIdx = -1u, LHSValIdx = -1u;
unsigned RHSIdx = -1u, RHSValIdx = -1u;
bool LHSUniform = true;
bool RHSUniform = true;
for (unsigned i = 0; i < VWidth; i++) {
unsigned MaskVal = Shuffle->getMaskValue(i);
if (MaskVal == -1u) {
UndefElts.setBit(i);
} else if (!DemandedElts[i]) {
NewUndefElts = true;
UndefElts.setBit(i);
} else if (MaskVal < LHSVWidth) {
if (LHSUndefElts[MaskVal]) {
NewUndefElts = true;
UndefElts.setBit(i);
} else {
LHSIdx = LHSIdx == -1u ? i : LHSVWidth;
LHSValIdx = LHSValIdx == -1u ? MaskVal : LHSVWidth;
LHSUniform = LHSUniform && (MaskVal == i);
}
} else {
if (RHSUndefElts[MaskVal - LHSVWidth]) {
NewUndefElts = true;
UndefElts.setBit(i);
} else {
RHSIdx = RHSIdx == -1u ? i : LHSVWidth;
RHSValIdx = RHSValIdx == -1u ? MaskVal - LHSVWidth : LHSVWidth;
RHSUniform = RHSUniform && (MaskVal - LHSVWidth == i);
}
}
}
// Try to transform shuffle with constant vector and single element from
// this constant vector to single insertelement instruction.
// shufflevector V, C, <v1, v2, .., ci, .., vm> ->
// insertelement V, C[ci], ci-n
if (LHSVWidth == Shuffle->getType()->getNumElements()) {
Value *Op = nullptr;
Constant *Value = nullptr;
unsigned Idx = -1u;
// Find constant vector with the single element in shuffle (LHS or RHS).
if (LHSIdx < LHSVWidth && RHSUniform) {
if (auto *CV = dyn_cast<ConstantVector>(Shuffle->getOperand(0))) {
Op = Shuffle->getOperand(1);
Value = CV->getOperand(LHSValIdx);
Idx = LHSIdx;
}
}
if (RHSIdx < LHSVWidth && LHSUniform) {
if (auto *CV = dyn_cast<ConstantVector>(Shuffle->getOperand(1))) {
Op = Shuffle->getOperand(0);
Value = CV->getOperand(RHSValIdx);
Idx = RHSIdx;
}
}
// Found constant vector with single element - convert to insertelement.
if (Op && Value) {
Instruction *New = InsertElementInst::Create(
Op, Value, ConstantInt::get(Type::getInt32Ty(I->getContext()), Idx),
Shuffle->getName());
InsertNewInstWith(New, *Shuffle);
return New;
}
}
if (NewUndefElts) {
// Add additional discovered undefs.
SmallVector<Constant*, 16> 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::Select: {
APInt LeftDemanded(DemandedElts), RightDemanded(DemandedElts);
if (ConstantVector* CV = dyn_cast<ConstantVector>(I->getOperand(0))) {
for (unsigned i = 0; i < VWidth; i++) {
Constant *CElt = CV->getAggregateElement(i);
// Method isNullValue always returns false when called on a
// ConstantExpr. If CElt is a ConstantExpr then skip it in order to
// to avoid propagating incorrect information.
if (isa<ConstantExpr>(CElt))
continue;
if (CElt->isNullValue())
LeftDemanded.clearBit(i);
else
RightDemanded.clearBit(i);
}
}
TmpV = SimplifyDemandedVectorElts(I->getOperand(1), LeftDemanded, UndefElts,
Depth + 1);
if (TmpV) { I->setOperand(1, TmpV); MadeChange = true; }
TmpV = SimplifyDemandedVectorElts(I->getOperand(2), RightDemanded,
UndefElts2, Depth + 1);
if (TmpV) { I->setOperand(2, TmpV); MadeChange = true; }
// Output elements are undefined if both are undefined.
UndefElts &= UndefElts2;
break;
}
case Instruction::BitCast: {
// Vector->vector casts only.
VectorType *VTy = dyn_cast<VectorType>(I->getOperand(0)->getType());
if (!VTy) break;
unsigned InVWidth = VTy->getNumElements();
APInt InputDemandedElts(InVWidth, 0);
UndefElts2 = APInt(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) == 0) {
// If the number of elements in the output is a multiple of the number of
// elements in the input 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.setBit(OutIdx / Ratio);
} else if ((InVWidth % VWidth) == 0) {
// If the number of elements in the input is a multiple of the number of
// elements in the output 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.setBit(InIdx);
} else {
// Unsupported so far.
break;
}
// 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;
}
if (VWidth == InVWidth) {
UndefElts = UndefElts2;
} else if ((VWidth % InVWidth) == 0) {
// If the number of elements in the output is a multiple of the number of
// elements in the input 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.setBit(OutIdx);
} else if ((InVWidth % VWidth) == 0) {
// If the number of elements in the input is a multiple of the number of
// elements in the output then an output element is undef if all of the
// corresponding input elements are undef.
for (unsigned OutIdx = 0; OutIdx != VWidth; ++OutIdx) {
APInt SubUndef = UndefElts2.lshr(OutIdx * Ratio).zextOrTrunc(Ratio);
if (SubUndef.countPopulation() == Ratio)
UndefElts.setBit(OutIdx);
}
} else {
llvm_unreachable("Unimp");
}
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::FPTrunc:
case Instruction::FPExt:
TmpV = SimplifyDemandedVectorElts(I->getOperand(0), DemandedElts, UndefElts,
Depth + 1);
if (TmpV) { I->setOperand(0, TmpV); MadeChange = true; }
break;
case Instruction::Call: {
IntrinsicInst *II = dyn_cast<IntrinsicInst>(I);
if (!II) break;
switch (II->getIntrinsicID()) {
default: break;
case Intrinsic::x86_xop_vfrcz_ss:
case Intrinsic::x86_xop_vfrcz_sd:
// The instructions for these intrinsics are speced to zero upper bits not
// pass them through like other scalar intrinsics. So we shouldn't just
// use Arg0 if DemandedElts[0] is clear like we do for other intrinsics.
// Instead we should return a zero vector.
if (!DemandedElts[0]) {
Worklist.Add(II);
return ConstantAggregateZero::get(II->getType());
}
// Only the lower element is used.
DemandedElts = 1;
TmpV = SimplifyDemandedVectorElts(II->getArgOperand(0), DemandedElts,
UndefElts, Depth + 1);
if (TmpV) { II->setArgOperand(0, TmpV); MadeChange = true; }
// Only the lower element is undefined. The high elements are zero.
UndefElts = UndefElts[0];
break;
// Unary scalar-as-vector operations that work column-wise.
case Intrinsic::x86_sse_rcp_ss:
case Intrinsic::x86_sse_rsqrt_ss:
case Intrinsic::x86_sse_sqrt_ss:
case Intrinsic::x86_sse2_sqrt_sd:
TmpV = SimplifyDemandedVectorElts(II->getArgOperand(0), DemandedElts,
UndefElts, Depth + 1);
if (TmpV) { II->setArgOperand(0, TmpV); MadeChange = true; }
// If lowest element of a scalar op isn't used then use Arg0.
if (!DemandedElts[0]) {
Worklist.Add(II);
return II->getArgOperand(0);
}
// TODO: If only low elt lower SQRT to FSQRT (with rounding/exceptions
// checks).
break;
// Binary scalar-as-vector operations that work column-wise. The high
// elements come from operand 0. The low element is a function of both
// operands.
case Intrinsic::x86_sse_min_ss:
case Intrinsic::x86_sse_max_ss:
case Intrinsic::x86_sse_cmp_ss:
case Intrinsic::x86_sse2_min_sd:
case Intrinsic::x86_sse2_max_sd:
case Intrinsic::x86_sse2_cmp_sd: {
TmpV = SimplifyDemandedVectorElts(II->getArgOperand(0), DemandedElts,
UndefElts, Depth + 1);
if (TmpV) { II->setArgOperand(0, TmpV); MadeChange = true; }
// If lowest element of a scalar op isn't used then use Arg0.
if (!DemandedElts[0]) {
Worklist.Add(II);
return II->getArgOperand(0);
}
// Only lower element is used for operand 1.
DemandedElts = 1;
TmpV = SimplifyDemandedVectorElts(II->getArgOperand(1), DemandedElts,
UndefElts2, Depth + 1);
if (TmpV) { II->setArgOperand(1, TmpV); MadeChange = true; }
// Lower element is undefined if both lower elements are undefined.
// Consider things like undef&0. The result is known zero, not undef.
if (!UndefElts2[0])
UndefElts.clearBit(0);
break;
}
// Binary scalar-as-vector operations that work column-wise. The high
// elements come from operand 0 and the low element comes from operand 1.
case Intrinsic::x86_sse41_round_ss:
case Intrinsic::x86_sse41_round_sd: {
// Don't use the low element of operand 0.
APInt DemandedElts2 = DemandedElts;
DemandedElts2.clearBit(0);
TmpV = SimplifyDemandedVectorElts(II->getArgOperand(0), DemandedElts2,
UndefElts, Depth + 1);
if (TmpV) { II->setArgOperand(0, TmpV); MadeChange = true; }
// If lowest element of a scalar op isn't used then use Arg0.
if (!DemandedElts[0]) {
Worklist.Add(II);
return II->getArgOperand(0);
}
// Only lower element is used for operand 1.
DemandedElts = 1;
TmpV = SimplifyDemandedVectorElts(II->getArgOperand(1), DemandedElts,
UndefElts2, Depth + 1);
if (TmpV) { II->setArgOperand(1, TmpV); MadeChange = true; }
// Take the high undef elements from operand 0 and take the lower element
// from operand 1.
UndefElts.clearBit(0);
UndefElts |= UndefElts2[0];
break;
}
// Three input scalar-as-vector operations that work column-wise. The high
// elements come from operand 0 and the low element is a function of all
// three inputs.
case Intrinsic::x86_avx512_mask_add_ss_round:
case Intrinsic::x86_avx512_mask_div_ss_round:
case Intrinsic::x86_avx512_mask_mul_ss_round:
case Intrinsic::x86_avx512_mask_sub_ss_round:
case Intrinsic::x86_avx512_mask_max_ss_round:
case Intrinsic::x86_avx512_mask_min_ss_round:
case Intrinsic::x86_avx512_mask_add_sd_round:
case Intrinsic::x86_avx512_mask_div_sd_round:
case Intrinsic::x86_avx512_mask_mul_sd_round:
case Intrinsic::x86_avx512_mask_sub_sd_round:
case Intrinsic::x86_avx512_mask_max_sd_round:
case Intrinsic::x86_avx512_mask_min_sd_round:
case Intrinsic::x86_fma_vfmadd_ss:
case Intrinsic::x86_fma_vfmsub_ss:
case Intrinsic::x86_fma_vfnmadd_ss:
case Intrinsic::x86_fma_vfnmsub_ss:
case Intrinsic::x86_fma_vfmadd_sd:
case Intrinsic::x86_fma_vfmsub_sd:
case Intrinsic::x86_fma_vfnmadd_sd:
case Intrinsic::x86_fma_vfnmsub_sd:
case Intrinsic::x86_avx512_mask_vfmadd_ss:
case Intrinsic::x86_avx512_mask_vfmadd_sd:
case Intrinsic::x86_avx512_maskz_vfmadd_ss:
case Intrinsic::x86_avx512_maskz_vfmadd_sd:
TmpV = SimplifyDemandedVectorElts(II->getArgOperand(0), DemandedElts,
UndefElts, Depth + 1);
if (TmpV) { II->setArgOperand(0, TmpV); MadeChange = true; }
// If lowest element of a scalar op isn't used then use Arg0.
if (!DemandedElts[0]) {
Worklist.Add(II);
return II->getArgOperand(0);
}
// Only lower element is used for operand 1 and 2.
DemandedElts = 1;
TmpV = SimplifyDemandedVectorElts(II->getArgOperand(1), DemandedElts,
UndefElts2, Depth + 1);
if (TmpV) { II->setArgOperand(1, TmpV); MadeChange = true; }
TmpV = SimplifyDemandedVectorElts(II->getArgOperand(2), DemandedElts,
UndefElts3, Depth + 1);
if (TmpV) { II->setArgOperand(2, TmpV); MadeChange = true; }
// Lower element is undefined if all three lower elements are undefined.
// Consider things like undef&0. The result is known zero, not undef.
if (!UndefElts2[0] || !UndefElts3[0])
UndefElts.clearBit(0);
break;
case Intrinsic::x86_avx512_mask3_vfmadd_ss:
case Intrinsic::x86_avx512_mask3_vfmadd_sd:
case Intrinsic::x86_avx512_mask3_vfmsub_ss:
case Intrinsic::x86_avx512_mask3_vfmsub_sd:
case Intrinsic::x86_avx512_mask3_vfnmsub_ss:
case Intrinsic::x86_avx512_mask3_vfnmsub_sd:
// These intrinsics get the passthru bits from operand 2.
TmpV = SimplifyDemandedVectorElts(II->getArgOperand(2), DemandedElts,
UndefElts, Depth + 1);
if (TmpV) { II->setArgOperand(2, TmpV); MadeChange = true; }
// If lowest element of a scalar op isn't used then use Arg2.
if (!DemandedElts[0]) {
Worklist.Add(II);
return II->getArgOperand(2);
}
// Only lower element is used for operand 0 and 1.
DemandedElts = 1;
TmpV = SimplifyDemandedVectorElts(II->getArgOperand(0), DemandedElts,
UndefElts2, Depth + 1);
if (TmpV) { II->setArgOperand(0, TmpV); MadeChange = true; }
TmpV = SimplifyDemandedVectorElts(II->getArgOperand(1), DemandedElts,
UndefElts3, Depth + 1);
if (TmpV) { II->setArgOperand(1, TmpV); MadeChange = true; }
// Lower element is undefined if all three lower elements are undefined.
// Consider things like undef&0. The result is known zero, not undef.
if (!UndefElts2[0] || !UndefElts3[0])
UndefElts.clearBit(0);
break;
case Intrinsic::x86_sse2_pmulu_dq:
case Intrinsic::x86_sse41_pmuldq:
case Intrinsic::x86_avx2_pmul_dq:
case Intrinsic::x86_avx2_pmulu_dq:
case Intrinsic::x86_avx512_pmul_dq_512:
case Intrinsic::x86_avx512_pmulu_dq_512: {
Value *Op0 = II->getArgOperand(0);
Value *Op1 = II->getArgOperand(1);
unsigned InnerVWidth = Op0->getType()->getVectorNumElements();
assert((VWidth * 2) == InnerVWidth && "Unexpected input size");
APInt InnerDemandedElts(InnerVWidth, 0);
for (unsigned i = 0; i != VWidth; ++i)
if (DemandedElts[i])
InnerDemandedElts.setBit(i * 2);
UndefElts2 = APInt(InnerVWidth, 0);
TmpV = SimplifyDemandedVectorElts(Op0, InnerDemandedElts, UndefElts2,
Depth + 1);
if (TmpV) { II->setArgOperand(0, TmpV); MadeChange = true; }
UndefElts3 = APInt(InnerVWidth, 0);
TmpV = SimplifyDemandedVectorElts(Op1, InnerDemandedElts, UndefElts3,
Depth + 1);
if (TmpV) { II->setArgOperand(1, TmpV); MadeChange = true; }
break;
}
case Intrinsic::x86_ssse3_pshuf_b_128:
case Intrinsic::x86_avx2_pshuf_b:
case Intrinsic::x86_avx512_pshuf_b_512: {
Value *Op1 = II->getArgOperand(1);
TmpV = SimplifyDemandedVectorElts(Op1, DemandedElts, UndefElts,
Depth + 1);
if (TmpV) { II->setArgOperand(1, TmpV); MadeChange = true; }
break;
}
// SSE4A instructions leave the upper 64-bits of the 128-bit result
// in an undefined state.
case Intrinsic::x86_sse4a_extrq:
case Intrinsic::x86_sse4a_extrqi:
case Intrinsic::x86_sse4a_insertq:
case Intrinsic::x86_sse4a_insertqi:
UndefElts |= APInt::getHighBitsSet(VWidth, VWidth / 2);
break;
}
break;
}
}
return MadeChange ? I : nullptr;
}
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