Example #1
0
/// truncate - Return a new range in the specified integer type, which must be
/// strictly smaller than the current type.  The returned range will
/// correspond to the possible range of values as if the source range had been
/// truncated to the specified type.
ConstantRange ConstantRange::truncate(uint32_t DstTySize) const {
  unsigned SrcTySize = getBitWidth();
  assert(SrcTySize > DstTySize && "Not a value truncation");
  APInt Size(APInt::getLowBitsSet(SrcTySize, DstTySize));
  if (isFullSet() || getSetSize().ugt(Size))
    return ConstantRange(DstTySize);

  APInt L = Lower; L.trunc(DstTySize);
  APInt U = Upper; U.trunc(DstTySize);
  return ConstantRange(L, U);
}
Example #2
0
APInt swift::constantFoldCast(APInt val, const BuiltinInfo &BI) {
  // Get the cast result.
  Type SrcTy = BI.Types[0];
  Type DestTy = BI.Types.size() == 2 ? BI.Types[1] : Type();
  uint32_t SrcBitWidth =
  SrcTy->castTo<BuiltinIntegerType>()->getGreatestWidth();
  uint32_t DestBitWidth =
  DestTy->castTo<BuiltinIntegerType>()->getGreatestWidth();
  
  APInt CastResV;
  if (SrcBitWidth == DestBitWidth) {
    return val;
  } else switch (BI.ID) {
    default : llvm_unreachable("Invalid case.");
    case BuiltinValueKind::Trunc:
    case BuiltinValueKind::TruncOrBitCast:
      return val.trunc(DestBitWidth);
    case BuiltinValueKind::ZExt:
    case BuiltinValueKind::ZExtOrBitCast:
      return val.zext(DestBitWidth);
      break;
    case BuiltinValueKind::SExt:
    case BuiltinValueKind::SExtOrBitCast:
      return val.sext(DestBitWidth);
  }
}
Example #3
0
/// truncate - Return a new range in the specified integer type, which must be
/// strictly smaller than the current type.  The returned range will
/// correspond to the possible range of values as if the source range had been
/// truncated to the specified type.
ConstantRange ConstantRange::truncate(uint32_t DstTySize) const {
  assert(getBitWidth() > DstTySize && "Not a value truncation");
  if (isEmptySet())
    return ConstantRange(DstTySize, /*isFullSet=*/false);
  if (isFullSet())
    return ConstantRange(DstTySize, /*isFullSet=*/true);

  APInt MaxValue = APInt::getMaxValue(DstTySize).zext(getBitWidth());
  APInt MaxBitValue(getBitWidth(), 0);
  MaxBitValue.setBit(DstTySize);

  APInt LowerDiv(Lower), UpperDiv(Upper);
  ConstantRange Union(DstTySize, /*isFullSet=*/false);

  // Analyze wrapped sets in their two parts: [0, Upper) \/ [Lower, MaxValue]
  // We use the non-wrapped set code to analyze the [Lower, MaxValue) part, and
  // then we do the union with [MaxValue, Upper)
  if (isWrappedSet()) {
    // if Upper is greater than Max Value, it covers the whole truncated range.
    if (Upper.uge(MaxValue))
      return ConstantRange(DstTySize, /*isFullSet=*/true);

    Union = ConstantRange(APInt::getMaxValue(DstTySize),Upper.trunc(DstTySize));
    UpperDiv = APInt::getMaxValue(getBitWidth());

    // Union covers the MaxValue case, so return if the remaining range is just
    // MaxValue.
    if (LowerDiv == UpperDiv)
      return Union;
  }

  // Chop off the most significant bits that are past the destination bitwidth.
  if (LowerDiv.uge(MaxValue)) {
    APInt Div(getBitWidth(), 0);
    APInt::udivrem(LowerDiv, MaxBitValue, Div, LowerDiv);
    UpperDiv = UpperDiv - MaxBitValue * Div;
  }

  if (UpperDiv.ule(MaxValue))
    return ConstantRange(LowerDiv.trunc(DstTySize),
                         UpperDiv.trunc(DstTySize)).unionWith(Union);

  // The truncated value wrapps around. Check if we can do better than fullset.
  APInt UpperModulo = UpperDiv - MaxBitValue;
  if (UpperModulo.ult(LowerDiv))
    return ConstantRange(LowerDiv.trunc(DstTySize),
                         UpperModulo.trunc(DstTySize)).unionWith(Union);

  return ConstantRange(DstTySize, /*isFullSet=*/true);
}
Example #4
0
/// isBytewiseValue - If the specified value can be set by repeating the same
/// byte in memory, return the i8 value that it is represented with.  This is
/// true for all i8 values obviously, but is also true for i32 0, i32 -1,
/// i16 0xF0F0, double 0.0 etc.  If the value can't be handled with a repeated
/// byte store (e.g. i16 0x1234), return null.
static Value *isBytewiseValue(Value *V) {
  LLVMContext &Context = V->getContext();
  
  // All byte-wide stores are splatable, even of arbitrary variables.
  if (V->getType()->isIntegerTy(8)) return V;
  
  // Constant float and double values can be handled as integer values if the
  // corresponding integer value is "byteable".  An important case is 0.0. 
  if (ConstantFP *CFP = dyn_cast<ConstantFP>(V)) {
    if (CFP->getType()->isFloatTy())
      V = ConstantExpr::getBitCast(CFP, Type::getInt32Ty(Context));
    if (CFP->getType()->isDoubleTy())
      V = ConstantExpr::getBitCast(CFP, Type::getInt64Ty(Context));
    // Don't handle long double formats, which have strange constraints.
  }
  
  // We can handle constant integers that are power of two in size and a 
  // multiple of 8 bits.
  if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) {
    unsigned Width = CI->getBitWidth();
    if (isPowerOf2_32(Width) && Width > 8) {
      // We can handle this value if the recursive binary decomposition is the
      // same at all levels.
      APInt Val = CI->getValue();
      APInt Val2;
      while (Val.getBitWidth() != 8) {
        unsigned NextWidth = Val.getBitWidth()/2;
        Val2  = Val.lshr(NextWidth);
        Val2.trunc(Val.getBitWidth()/2);
        Val.trunc(Val.getBitWidth()/2);

        // If the top/bottom halves aren't the same, reject it.
        if (Val != Val2)
          return 0;
      }
      return ConstantInt::get(Context, Val);
    }
  }
  
  // Conceptually, we could handle things like:
  //   %a = zext i8 %X to i16
  //   %b = shl i16 %a, 8
  //   %c = or i16 %a, %b
  // but until there is an example that actually needs this, it doesn't seem
  // worth worrying about.
  return 0;
}
Example #5
0
llvm::Constant *irgen::emitConstantInt(IRGenModule &IGM,
                                       IntegerLiteralInst *ILI) {
  APInt value = ILI->getValue();
  BuiltinIntegerWidth width
    = ILI->getType().castTo<BuiltinIntegerType>()->getWidth();

  // The value may need truncation if its type had an abstract size.
  if (!width.isFixedWidth()) {
    assert(width.isPointerWidth() && "impossible width value");

    unsigned pointerWidth = IGM.getPointerSize().getValueInBits();
    assert(pointerWidth <= value.getBitWidth()
           && "lost precision at AST/SIL level?!");
    if (pointerWidth < value.getBitWidth())
      value = value.trunc(pointerWidth);
  }

  return llvm::ConstantInt::get(IGM.LLVMContext, value);
}
Example #6
0
void BDCE::determineLiveOperandBits(const Instruction *UserI,
                                    const Instruction *I, unsigned OperandNo,
                                    const APInt &AOut, APInt &AB,
                                    APInt &KnownZero, APInt &KnownOne,
                                    APInt &KnownZero2, APInt &KnownOne2) {
  unsigned BitWidth = AB.getBitWidth();

  // We're called once per operand, but for some instructions, we need to
  // compute known bits of both operands in order to determine the live bits of
  // either (when both operands are instructions themselves). We don't,
  // however, want to do this twice, so we cache the result in APInts that live
  // in the caller. For the two-relevant-operands case, both operand values are
  // provided here.
  auto ComputeKnownBits =
      [&](unsigned BitWidth, const Value *V1, const Value *V2) {
        const DataLayout &DL = I->getModule()->getDataLayout();
        KnownZero = APInt(BitWidth, 0);
        KnownOne = APInt(BitWidth, 0);
        computeKnownBits(const_cast<Value *>(V1), KnownZero, KnownOne, DL, 0,
                         AC, UserI, DT);

        if (V2) {
          KnownZero2 = APInt(BitWidth, 0);
          KnownOne2 = APInt(BitWidth, 0);
          computeKnownBits(const_cast<Value *>(V2), KnownZero2, KnownOne2, DL,
                           0, AC, UserI, DT);
        }
      };

  switch (UserI->getOpcode()) {
  default: break;
  case Instruction::Call:
  case Instruction::Invoke:
    if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(UserI))
      switch (II->getIntrinsicID()) {
      default: break;
      case Intrinsic::bswap:
        // The alive bits of the input are the swapped alive bits of
        // the output.
        AB = AOut.byteSwap();
        break;
      case Intrinsic::ctlz:
        if (OperandNo == 0) {
          // We need some output bits, so we need all bits of the
          // input to the left of, and including, the leftmost bit
          // known to be one.
          ComputeKnownBits(BitWidth, I, nullptr);
          AB = APInt::getHighBitsSet(BitWidth,
                 std::min(BitWidth, KnownOne.countLeadingZeros()+1));
        }
        break;
      case Intrinsic::cttz:
        if (OperandNo == 0) {
          // We need some output bits, so we need all bits of the
          // input to the right of, and including, the rightmost bit
          // known to be one.
          ComputeKnownBits(BitWidth, I, nullptr);
          AB = APInt::getLowBitsSet(BitWidth,
                 std::min(BitWidth, KnownOne.countTrailingZeros()+1));
        }
        break;
      }
    break;
  case Instruction::Add:
  case Instruction::Sub:
    // Find the highest live output bit. We don't need any more input
    // bits than that (adds, and thus subtracts, ripple only to the
    // left).
    AB = APInt::getLowBitsSet(BitWidth, AOut.getActiveBits());
    break;
  case Instruction::Shl:
    if (OperandNo == 0)
      if (ConstantInt *CI =
            dyn_cast<ConstantInt>(UserI->getOperand(1))) {
        uint64_t ShiftAmt = CI->getLimitedValue(BitWidth-1);
        AB = AOut.lshr(ShiftAmt);

        // If the shift is nuw/nsw, then the high bits are not dead
        // (because we've promised that they *must* be zero).
        const ShlOperator *S = cast<ShlOperator>(UserI);
        if (S->hasNoSignedWrap())
          AB |= APInt::getHighBitsSet(BitWidth, ShiftAmt+1);
        else if (S->hasNoUnsignedWrap())
          AB |= APInt::getHighBitsSet(BitWidth, ShiftAmt);
      }
    break;
  case Instruction::LShr:
    if (OperandNo == 0)
      if (ConstantInt *CI =
            dyn_cast<ConstantInt>(UserI->getOperand(1))) {
        uint64_t ShiftAmt = CI->getLimitedValue(BitWidth-1);
        AB = AOut.shl(ShiftAmt);

        // If the shift is exact, then the low bits are not dead
        // (they must be zero).
        if (cast<LShrOperator>(UserI)->isExact())
          AB |= APInt::getLowBitsSet(BitWidth, ShiftAmt);
      }
    break;
  case Instruction::AShr:
    if (OperandNo == 0)
      if (ConstantInt *CI =
            dyn_cast<ConstantInt>(UserI->getOperand(1))) {
        uint64_t ShiftAmt = CI->getLimitedValue(BitWidth-1);
        AB = AOut.shl(ShiftAmt);
        // Because the high input bit is replicated into the
        // high-order bits of the result, if we need any of those
        // bits, then we must keep the highest input bit.
        if ((AOut & APInt::getHighBitsSet(BitWidth, ShiftAmt))
            .getBoolValue())
          AB.setBit(BitWidth-1);

        // If the shift is exact, then the low bits are not dead
        // (they must be zero).
        if (cast<AShrOperator>(UserI)->isExact())
          AB |= APInt::getLowBitsSet(BitWidth, ShiftAmt);
      }
    break;
  case Instruction::And:
    AB = AOut;

    // For bits that are known zero, the corresponding bits in the
    // other operand are dead (unless they're both zero, in which
    // case they can't both be dead, so just mark the LHS bits as
    // dead).
    if (OperandNo == 0) {
      ComputeKnownBits(BitWidth, I, UserI->getOperand(1));
      AB &= ~KnownZero2;
    } else {
      if (!isa<Instruction>(UserI->getOperand(0)))
        ComputeKnownBits(BitWidth, UserI->getOperand(0), I);
      AB &= ~(KnownZero & ~KnownZero2);
    }
    break;
  case Instruction::Or:
    AB = AOut;

    // For bits that are known one, the corresponding bits in the
    // other operand are dead (unless they're both one, in which
    // case they can't both be dead, so just mark the LHS bits as
    // dead).
    if (OperandNo == 0) {
      ComputeKnownBits(BitWidth, I, UserI->getOperand(1));
      AB &= ~KnownOne2;
    } else {
      if (!isa<Instruction>(UserI->getOperand(0)))
        ComputeKnownBits(BitWidth, UserI->getOperand(0), I);
      AB &= ~(KnownOne & ~KnownOne2);
    }
    break;
  case Instruction::Xor:
  case Instruction::PHI:
    AB = AOut;
    break;
  case Instruction::Trunc:
    AB = AOut.zext(BitWidth);
    break;
  case Instruction::ZExt:
    AB = AOut.trunc(BitWidth);
    break;
  case Instruction::SExt:
    AB = AOut.trunc(BitWidth);
    // Because the high input bit is replicated into the
    // high-order bits of the result, if we need any of those
    // bits, then we must keep the highest input bit.
    if ((AOut & APInt::getHighBitsSet(AOut.getBitWidth(),
                                      AOut.getBitWidth() - BitWidth))
        .getBoolValue())
      AB.setBit(BitWidth-1);
    break;
  case Instruction::Select:
    if (OperandNo != 0)
      AB = AOut;
    break;
  }
}
/// ComputeMaskedBits - Determine which of the bits specified in Mask are
/// known to be either zero or one and return them in the KnownZero/KnownOne
/// bit sets.  This code only analyzes bits in Mask, in order to short-circuit
/// processing.
/// NOTE: we cannot consider 'undef' to be "IsZero" here.  The problem is that
/// we cannot optimize based on the assumption that it is zero without changing
/// it to be an explicit zero.  If we don't change it to zero, other code could
/// optimized based on the contradictory assumption that it is non-zero.
/// Because instcombine aggressively folds operations with undef args anyway,
/// this won't lose us code quality.
void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
                             APInt &KnownZero, APInt &KnownOne,
                             TargetData *TD, unsigned Depth) {
  const unsigned MaxDepth = 6;
  assert(V && "No Value?");
  assert(Depth <= MaxDepth && "Limit Search Depth");
  unsigned BitWidth = Mask.getBitWidth();
  assert((V->getType()->isInteger() || isa<PointerType>(V->getType())) &&
         "Not integer or pointer type!");
  assert((!TD || TD->getTypeSizeInBits(V->getType()) == BitWidth) &&
         (!isa<IntegerType>(V->getType()) ||
          V->getType()->getPrimitiveSizeInBits() == BitWidth) &&
         KnownZero.getBitWidth() == BitWidth && 
         KnownOne.getBitWidth() == BitWidth &&
         "V, Mask, KnownOne and KnownZero should have same BitWidth");

  if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) {
    // We know all of the bits for a constant!
    KnownOne = CI->getValue() & Mask;
    KnownZero = ~KnownOne & Mask;
    return;
  }
  // Null is all-zeros.
  if (isa<ConstantPointerNull>(V)) {
    KnownOne.clear();
    KnownZero = Mask;
    return;
  }
  // The address of an aligned GlobalValue has trailing zeros.
  if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
    unsigned Align = GV->getAlignment();
    if (Align == 0 && TD && GV->getType()->getElementType()->isSized()) 
      Align = TD->getPrefTypeAlignment(GV->getType()->getElementType());
    if (Align > 0)
      KnownZero = Mask & APInt::getLowBitsSet(BitWidth,
                                              CountTrailingZeros_32(Align));
    else
      KnownZero.clear();
    KnownOne.clear();
    return;
  }

  KnownZero.clear(); KnownOne.clear();   // Start out not knowing anything.

  if (Depth == MaxDepth || Mask == 0)
    return;  // Limit search depth.

  User *I = dyn_cast<User>(V);
  if (!I) return;

  APInt KnownZero2(KnownZero), KnownOne2(KnownOne);
  switch (getOpcode(I)) {
  default: break;
  case Instruction::And: {
    // If either the LHS or the RHS are Zero, the result is zero.
    ComputeMaskedBits(I->getOperand(1), Mask, KnownZero, KnownOne, TD, Depth+1);
    APInt Mask2(Mask & ~KnownZero);
    ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, TD,
                      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 Instruction::Or: {
    ComputeMaskedBits(I->getOperand(1), Mask, KnownZero, KnownOne, TD, Depth+1);
    APInt Mask2(Mask & ~KnownOne);
    ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, TD,
                      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 Instruction::Xor: {
    ComputeMaskedBits(I->getOperand(1), Mask, KnownZero, KnownOne, TD, Depth+1);
    ComputeMaskedBits(I->getOperand(0), Mask, KnownZero2, KnownOne2, TD,
                      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.
    APInt 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 Instruction::Mul: {
    APInt Mask2 = APInt::getAllOnesValue(BitWidth);
    ComputeMaskedBits(I->getOperand(1), Mask2, KnownZero, KnownOne, TD,Depth+1);
    ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, TD,
                      Depth+1);
    assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); 
    assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?"); 
    
    // If low bits are zero in either operand, output low known-0 bits.
    // Also compute a conserative estimate for high known-0 bits.
    // More trickiness is possible, but this is sufficient for the
    // interesting case of alignment computation.
    KnownOne.clear();
    unsigned TrailZ = KnownZero.countTrailingOnes() +
                      KnownZero2.countTrailingOnes();
    unsigned LeadZ =  std::max(KnownZero.countLeadingOnes() +
                               KnownZero2.countLeadingOnes(),
                               BitWidth) - BitWidth;

    TrailZ = std::min(TrailZ, BitWidth);
    LeadZ = std::min(LeadZ, BitWidth);
    KnownZero = APInt::getLowBitsSet(BitWidth, TrailZ) |
                APInt::getHighBitsSet(BitWidth, LeadZ);
    KnownZero &= Mask;
    return;
  }
  case Instruction::UDiv: {
    // For the purposes of computing leading zeros we can conservatively
    // treat a udiv as a logical right shift by the power of 2 known to
    // be less than the denominator.
    APInt AllOnes = APInt::getAllOnesValue(BitWidth);
    ComputeMaskedBits(I->getOperand(0),
                      AllOnes, KnownZero2, KnownOne2, TD, Depth+1);
    unsigned LeadZ = KnownZero2.countLeadingOnes();

    KnownOne2.clear();
    KnownZero2.clear();
    ComputeMaskedBits(I->getOperand(1),
                      AllOnes, KnownZero2, KnownOne2, TD, Depth+1);
    unsigned RHSUnknownLeadingOnes = KnownOne2.countLeadingZeros();
    if (RHSUnknownLeadingOnes != BitWidth)
      LeadZ = std::min(BitWidth,
                       LeadZ + BitWidth - RHSUnknownLeadingOnes - 1);

    KnownZero = APInt::getHighBitsSet(BitWidth, LeadZ) & Mask;
    return;
  }
  case Instruction::Select:
    ComputeMaskedBits(I->getOperand(2), Mask, KnownZero, KnownOne, TD, Depth+1);
    ComputeMaskedBits(I->getOperand(1), Mask, KnownZero2, KnownOne2, TD,
                      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 Instruction::FPTrunc:
  case Instruction::FPExt:
  case Instruction::FPToUI:
  case Instruction::FPToSI:
  case Instruction::SIToFP:
  case Instruction::UIToFP:
    return; // Can't work with floating point.
  case Instruction::PtrToInt:
  case Instruction::IntToPtr:
    // We can't handle these if we don't know the pointer size.
    if (!TD) return;
    // FALL THROUGH and handle them the same as zext/trunc.
  case Instruction::ZExt:
  case Instruction::Trunc: {
    // Note that we handle pointer operands here because of inttoptr/ptrtoint
    // which fall through here.
    const Type *SrcTy = I->getOperand(0)->getType();
    unsigned SrcBitWidth = TD ?
      TD->getTypeSizeInBits(SrcTy) :
      SrcTy->getPrimitiveSizeInBits();
    APInt MaskIn(Mask);
    MaskIn.zextOrTrunc(SrcBitWidth);
    KnownZero.zextOrTrunc(SrcBitWidth);
    KnownOne.zextOrTrunc(SrcBitWidth);
    ComputeMaskedBits(I->getOperand(0), MaskIn, KnownZero, KnownOne, TD,
                      Depth+1);
    KnownZero.zextOrTrunc(BitWidth);
    KnownOne.zextOrTrunc(BitWidth);
    // Any top bits are known to be zero.
    if (BitWidth > SrcBitWidth)
      KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth);
    return;
  }
  case Instruction::BitCast: {
    const Type *SrcTy = I->getOperand(0)->getType();
    if (SrcTy->isInteger() || isa<PointerType>(SrcTy)) {
      ComputeMaskedBits(I->getOperand(0), Mask, KnownZero, KnownOne, TD,
                        Depth+1);
      return;
    }
    break;
  }
  case Instruction::SExt: {
    // Compute the bits in the result that are not present in the input.
    const IntegerType *SrcTy = cast<IntegerType>(I->getOperand(0)->getType());
    unsigned SrcBitWidth = SrcTy->getBitWidth();
      
    APInt MaskIn(Mask); 
    MaskIn.trunc(SrcBitWidth);
    KnownZero.trunc(SrcBitWidth);
    KnownOne.trunc(SrcBitWidth);
    ComputeMaskedBits(I->getOperand(0), MaskIn, KnownZero, KnownOne, TD,
                      Depth+1);
    assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); 
    KnownZero.zext(BitWidth);
    KnownOne.zext(BitWidth);

    // If the sign bit of the input is known set or clear, then we know the
    // top bits of the result.
    if (KnownZero[SrcBitWidth-1])             // Input sign bit known zero
      KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth);
    else if (KnownOne[SrcBitWidth-1])           // Input sign bit known set
      KnownOne |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth);
    return;
  }
  case Instruction::Shl:
    // (shl X, C1) & C2 == 0   iff   (X & C2 >>u C1) == 0
    if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) {
      uint64_t ShiftAmt = SA->getLimitedValue(BitWidth);
      APInt Mask2(Mask.lshr(ShiftAmt));
      ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero, KnownOne, TD,
                        Depth+1);
      assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); 
      KnownZero <<= ShiftAmt;
      KnownOne  <<= ShiftAmt;
      KnownZero |= APInt::getLowBitsSet(BitWidth, ShiftAmt); // low bits known 0
      return;
    }
    break;
  case Instruction::LShr:
    // (ushr X, C1) & C2 == 0   iff  (-1 >> C1) & C2 == 0
    if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) {
      // Compute the new bits that are at the top now.
      uint64_t ShiftAmt = SA->getLimitedValue(BitWidth);
      
      // Unsigned shift right.
      APInt Mask2(Mask.shl(ShiftAmt));
      ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero,KnownOne, TD,
                        Depth+1);
      assert((KnownZero & KnownOne) == 0&&"Bits known to be one AND zero?"); 
      KnownZero = APIntOps::lshr(KnownZero, ShiftAmt);
      KnownOne  = APIntOps::lshr(KnownOne, ShiftAmt);
      // high bits known zero.
      KnownZero |= APInt::getHighBitsSet(BitWidth, ShiftAmt);
      return;
    }
    break;
  case Instruction::AShr:
    // (ashr X, C1) & C2 == 0   iff  (-1 >> C1) & C2 == 0
    if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) {
      // Compute the new bits that are at the top now.
      uint64_t ShiftAmt = SA->getLimitedValue(BitWidth);
      
      // Signed shift right.
      APInt Mask2(Mask.shl(ShiftAmt));
      ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero, KnownOne, TD,
                        Depth+1);
      assert((KnownZero & KnownOne) == 0&&"Bits known to be one AND zero?"); 
      KnownZero = APIntOps::lshr(KnownZero, ShiftAmt);
      KnownOne  = APIntOps::lshr(KnownOne, ShiftAmt);
        
      APInt HighBits(APInt::getHighBitsSet(BitWidth, ShiftAmt));
      if (KnownZero[BitWidth-ShiftAmt-1])    // New bits are known zero.
        KnownZero |= HighBits;
      else if (KnownOne[BitWidth-ShiftAmt-1])  // New bits are known one.
        KnownOne |= HighBits;
      return;
    }
    break;
  case Instruction::Sub: {
    if (ConstantInt *CLHS = dyn_cast<ConstantInt>(I->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.
      if (!CLHS->getValue().isNegative()) {
        unsigned NLZ = (CLHS->getValue()+1).countLeadingZeros();
        // NLZ can't be BitWidth with no sign bit
        APInt MaskV = APInt::getHighBitsSet(BitWidth, NLZ+1);
        ComputeMaskedBits(I->getOperand(1), MaskV, KnownZero2, KnownOne2,
                          TD, Depth+1);
    
        // If all of the MaskV bits are known to be zero, then we know the
        // output top bits are zero, because we now know that the output is
        // from [0-C].
        if ((KnownZero2 & MaskV) == MaskV) {
          unsigned NLZ2 = CLHS->getValue().countLeadingZeros();
          // Top bits known zero.
          KnownZero = APInt::getHighBitsSet(BitWidth, NLZ2) & Mask;
        }
      }        
    }
  }
  // fall through
  case Instruction::Add: {
    // If one of the operands has trailing zeros, than the bits that the
    // other operand has in those bit positions will be preserved in the
    // result. For an add, this works with either operand. For a subtract,
    // this only works if the known zeros are in the right operand.
    APInt LHSKnownZero(BitWidth, 0), LHSKnownOne(BitWidth, 0);
    APInt Mask2 = APInt::getLowBitsSet(BitWidth,
                                       BitWidth - Mask.countLeadingZeros());
    ComputeMaskedBits(I->getOperand(0), Mask2, LHSKnownZero, LHSKnownOne, TD,
                      Depth+1);
    assert((LHSKnownZero & LHSKnownOne) == 0 &&
           "Bits known to be one AND zero?");
    unsigned LHSKnownZeroOut = LHSKnownZero.countTrailingOnes();

    ComputeMaskedBits(I->getOperand(1), Mask2, KnownZero2, KnownOne2, TD, 
                      Depth+1);
    assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?"); 
    unsigned RHSKnownZeroOut = KnownZero2.countTrailingOnes();

    // Determine which operand has more trailing zeros, and use that
    // many bits from the other operand.
    if (LHSKnownZeroOut > RHSKnownZeroOut) {
      if (getOpcode(I) == Instruction::Add) {
        APInt Mask = APInt::getLowBitsSet(BitWidth, LHSKnownZeroOut);
        KnownZero |= KnownZero2 & Mask;
        KnownOne  |= KnownOne2 & Mask;
      } else {
        // If the known zeros are in the left operand for a subtract,
        // fall back to the minimum known zeros in both operands.
        KnownZero |= APInt::getLowBitsSet(BitWidth,
                                          std::min(LHSKnownZeroOut,
                                                   RHSKnownZeroOut));
      }
    } else if (RHSKnownZeroOut >= LHSKnownZeroOut) {
      APInt Mask = APInt::getLowBitsSet(BitWidth, RHSKnownZeroOut);
      KnownZero |= LHSKnownZero & Mask;
      KnownOne  |= LHSKnownOne & Mask;
    }
    return;
  }
  case Instruction::SRem:
    if (ConstantInt *Rem = dyn_cast<ConstantInt>(I->getOperand(1))) {
      APInt RA = Rem->getValue();
      if (RA.isPowerOf2() || (-RA).isPowerOf2()) {
        APInt LowBits = RA.isStrictlyPositive() ? (RA - 1) : ~RA;
        APInt Mask2 = LowBits | APInt::getSignBit(BitWidth);
        ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, TD, 
                          Depth+1);

        // If the sign bit of the first operand is zero, the sign bit of
        // the result is zero. If the first operand has no one bits below
        // the second operand's single 1 bit, its sign will be zero.
        if (KnownZero2[BitWidth-1] || ((KnownZero2 & LowBits) == LowBits))
          KnownZero2 |= ~LowBits;

        KnownZero |= KnownZero2 & Mask;

        assert((KnownZero & KnownOne) == 0&&"Bits known to be one AND zero?"); 
      }
    }
    break;
  case Instruction::URem: {
    if (ConstantInt *Rem = dyn_cast<ConstantInt>(I->getOperand(1))) {
      APInt RA = Rem->getValue();
      if (RA.isPowerOf2()) {
        APInt LowBits = (RA - 1);
        APInt Mask2 = LowBits & Mask;
        KnownZero |= ~LowBits & Mask;
        ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero, KnownOne, TD,
                          Depth+1);
        assert((KnownZero & KnownOne) == 0&&"Bits known to be one AND zero?");
        break;
      }
    }

    // Since the result is less than or equal to either operand, any leading
    // zero bits in either operand must also exist in the result.
    APInt AllOnes = APInt::getAllOnesValue(BitWidth);
    ComputeMaskedBits(I->getOperand(0), AllOnes, KnownZero, KnownOne,
                      TD, Depth+1);
    ComputeMaskedBits(I->getOperand(1), AllOnes, KnownZero2, KnownOne2,
                      TD, Depth+1);

    unsigned Leaders = std::max(KnownZero.countLeadingOnes(),
                                KnownZero2.countLeadingOnes());
    KnownOne.clear();
    KnownZero = APInt::getHighBitsSet(BitWidth, Leaders) & Mask;
    break;
  }

  case Instruction::Alloca:
  case Instruction::Malloc: {
    AllocationInst *AI = cast<AllocationInst>(V);
    unsigned Align = AI->getAlignment();
    if (Align == 0 && TD) {
      if (isa<AllocaInst>(AI))
        Align = TD->getABITypeAlignment(AI->getType()->getElementType());
      else if (isa<MallocInst>(AI)) {
        // Malloc returns maximally aligned memory.
        Align = TD->getABITypeAlignment(AI->getType()->getElementType());
        Align =
          std::max(Align,
                   (unsigned)TD->getABITypeAlignment(Type::DoubleTy));
        Align =
          std::max(Align,
                   (unsigned)TD->getABITypeAlignment(Type::Int64Ty));
      }
    }
    
    if (Align > 0)
      KnownZero = Mask & APInt::getLowBitsSet(BitWidth,
                                              CountTrailingZeros_32(Align));
    break;
  }
  case Instruction::GetElementPtr: {
    // Analyze all of the subscripts of this getelementptr instruction
    // to determine if we can prove known low zero bits.
    APInt LocalMask = APInt::getAllOnesValue(BitWidth);
    APInt LocalKnownZero(BitWidth, 0), LocalKnownOne(BitWidth, 0);
    ComputeMaskedBits(I->getOperand(0), LocalMask,
                      LocalKnownZero, LocalKnownOne, TD, Depth+1);
    unsigned TrailZ = LocalKnownZero.countTrailingOnes();

    gep_type_iterator GTI = gep_type_begin(I);
    for (unsigned i = 1, e = I->getNumOperands(); i != e; ++i, ++GTI) {
      Value *Index = I->getOperand(i);
      if (const StructType *STy = dyn_cast<StructType>(*GTI)) {
        // Handle struct member offset arithmetic.
        if (!TD) return;
        const StructLayout *SL = TD->getStructLayout(STy);
        unsigned Idx = cast<ConstantInt>(Index)->getZExtValue();
        uint64_t Offset = SL->getElementOffset(Idx);
        TrailZ = std::min(TrailZ,
                          CountTrailingZeros_64(Offset));
      } else {
        // Handle array index arithmetic.
        const Type *IndexedTy = GTI.getIndexedType();
        if (!IndexedTy->isSized()) return;
        unsigned GEPOpiBits = Index->getType()->getPrimitiveSizeInBits();
        uint64_t TypeSize = TD ? TD->getTypeAllocSize(IndexedTy) : 1;
        LocalMask = APInt::getAllOnesValue(GEPOpiBits);
        LocalKnownZero = LocalKnownOne = APInt(GEPOpiBits, 0);
        ComputeMaskedBits(Index, LocalMask,
                          LocalKnownZero, LocalKnownOne, TD, Depth+1);
        TrailZ = std::min(TrailZ,
                          unsigned(CountTrailingZeros_64(TypeSize) +
                                   LocalKnownZero.countTrailingOnes()));
      }
    }
    
    KnownZero = APInt::getLowBitsSet(BitWidth, TrailZ) & Mask;
    break;
  }
  case Instruction::PHI: {
    PHINode *P = cast<PHINode>(I);
    // Handle the case of a simple two-predecessor recurrence PHI.
    // There's a lot more that could theoretically be done here, but
    // this is sufficient to catch some interesting cases.
    if (P->getNumIncomingValues() == 2) {
      for (unsigned i = 0; i != 2; ++i) {
        Value *L = P->getIncomingValue(i);
        Value *R = P->getIncomingValue(!i);
        User *LU = dyn_cast<User>(L);
        if (!LU)
          continue;
        unsigned Opcode = getOpcode(LU);
        // Check for operations that have the property that if
        // both their operands have low zero bits, the result
        // will have low zero bits.
        if (Opcode == Instruction::Add ||
            Opcode == Instruction::Sub ||
            Opcode == Instruction::And ||
            Opcode == Instruction::Or ||
            Opcode == Instruction::Mul) {
          Value *LL = LU->getOperand(0);
          Value *LR = LU->getOperand(1);
          // Find a recurrence.
          if (LL == I)
            L = LR;
          else if (LR == I)
            L = LL;
          else
            break;
          // Ok, we have a PHI of the form L op= R. Check for low
          // zero bits.
          APInt Mask2 = APInt::getAllOnesValue(BitWidth);
          ComputeMaskedBits(R, Mask2, KnownZero2, KnownOne2, TD, Depth+1);
          Mask2 = APInt::getLowBitsSet(BitWidth,
                                       KnownZero2.countTrailingOnes());

          // We need to take the minimum number of known bits
          APInt KnownZero3(KnownZero), KnownOne3(KnownOne);
          ComputeMaskedBits(L, Mask2, KnownZero3, KnownOne3, TD, Depth+1);

          KnownZero = Mask &
                      APInt::getLowBitsSet(BitWidth,
                                           std::min(KnownZero2.countTrailingOnes(),
                                                    KnownZero3.countTrailingOnes()));
          break;
        }
      }
    }

    // Otherwise take the unions of the known bit sets of the operands,
    // taking conservative care to avoid excessive recursion.
    if (Depth < MaxDepth - 1 && !KnownZero && !KnownOne) {
      KnownZero = APInt::getAllOnesValue(BitWidth);
      KnownOne = APInt::getAllOnesValue(BitWidth);
      for (unsigned i = 0, e = P->getNumIncomingValues(); i != e; ++i) {
        // Skip direct self references.
        if (P->getIncomingValue(i) == P) continue;

        KnownZero2 = APInt(BitWidth, 0);
        KnownOne2 = APInt(BitWidth, 0);
        // Recurse, but cap the recursion to one level, because we don't
        // want to waste time spinning around in loops.
        ComputeMaskedBits(P->getIncomingValue(i), KnownZero | KnownOne,
                          KnownZero2, KnownOne2, TD, MaxDepth-1);
        KnownZero &= KnownZero2;
        KnownOne &= KnownOne2;
        // If all bits have been ruled out, there's no need to check
        // more operands.
        if (!KnownZero && !KnownOne)
          break;
      }
    }
    break;
  }
  case Instruction::Call:
    if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
      switch (II->getIntrinsicID()) {
      default: break;
      case Intrinsic::ctpop:
      case Intrinsic::ctlz:
      case Intrinsic::cttz: {
        unsigned LowBits = Log2_32(BitWidth)+1;
        KnownZero = APInt::getHighBitsSet(BitWidth, BitWidth - LowBits);
        break;
      }
      }
    }
    break;
  }
}
Example #8
0
SymbolicValue
ConstExprFunctionState::computeConstantValueBuiltin(BuiltinInst *inst) {
  const BuiltinInfo &builtin = inst->getBuiltinInfo();

  // Handle various cases in groups.
  auto unknownResult = [&]() -> SymbolicValue {
    return evaluator.getUnknown(SILValue(inst), UnknownReason::Default);
  };

  // Unary operations.
  if (inst->getNumOperands() == 1) {
    auto operand = getConstantValue(inst->getOperand(0));
    // TODO: Could add a "value used here" sort of diagnostic.
    if (!operand.isConstant())
      return operand;

    // TODO: SUCheckedConversion/USCheckedConversion

    // Implement support for s_to_s_checked_trunc_Int2048_Int64 and other
    // checking integer truncates.  These produce a tuple of the result value
    // and an overflow bit.
    //
    // TODO: We can/should diagnose statically detectable integer overflow
    // errors and subsume the ConstantFolding.cpp mandatory SIL pass.
    auto IntCheckedTruncFn = [&](bool srcSigned,
                                 bool dstSigned) -> SymbolicValue {
      if (operand.getKind() != SymbolicValue::Integer)
        return unknownResult();

      auto operandVal = operand.getIntegerValue();
      uint32_t srcBitWidth = operandVal.getBitWidth();
      auto dstBitWidth =
          builtin.Types[1]->castTo<BuiltinIntegerType>()->getGreatestWidth();

      APInt result = operandVal.trunc(dstBitWidth);

      // Compute the overflow by re-extending the value back to its source and
      // checking for loss of value.
      APInt reextended =
          dstSigned ? result.sext(srcBitWidth) : result.zext(srcBitWidth);
      bool overflowed = (operandVal != reextended);

      if (!srcSigned && dstSigned)
        overflowed |= result.isSignBitSet();

      if (overflowed)
        return evaluator.getUnknown(SILValue(inst), UnknownReason::Overflow);

      auto &astContext = evaluator.getASTContext();
      // Build the Symbolic value result for our truncated value.
      return SymbolicValue::getAggregate(
          {SymbolicValue::getInteger(result, astContext),
           SymbolicValue::getInteger(APInt(1, overflowed), astContext)},
          astContext);
    };

    switch (builtin.ID) {
    default:
      break;
    case BuiltinValueKind::SToSCheckedTrunc:
      return IntCheckedTruncFn(true, true);
    case BuiltinValueKind::UToSCheckedTrunc:
      return IntCheckedTruncFn(false, true);
    case BuiltinValueKind::SToUCheckedTrunc:
      return IntCheckedTruncFn(true, false);
    case BuiltinValueKind::UToUCheckedTrunc:
      return IntCheckedTruncFn(false, false);

    case BuiltinValueKind::Trunc:
    case BuiltinValueKind::TruncOrBitCast:
    case BuiltinValueKind::ZExt:
    case BuiltinValueKind::ZExtOrBitCast:
    case BuiltinValueKind::SExt:
    case BuiltinValueKind::SExtOrBitCast: {
      if (operand.getKind() != SymbolicValue::Integer)
        return unknownResult();

      unsigned destBitWidth =
          inst->getType().castTo<BuiltinIntegerType>()->getGreatestWidth();

      APInt result = operand.getIntegerValue();
      if (result.getBitWidth() != destBitWidth) {
        switch (builtin.ID) {
        default:
          assert(0 && "Unknown case");
        case BuiltinValueKind::Trunc:
        case BuiltinValueKind::TruncOrBitCast:
          result = result.trunc(destBitWidth);
          break;
        case BuiltinValueKind::ZExt:
        case BuiltinValueKind::ZExtOrBitCast:
          result = result.zext(destBitWidth);
          break;
        case BuiltinValueKind::SExt:
        case BuiltinValueKind::SExtOrBitCast:
          result = result.sext(destBitWidth);
          break;
        }
      }
      return SymbolicValue::getInteger(result, evaluator.getASTContext());
    }
    }
  }

  // Binary operations.
  if (inst->getNumOperands() == 2) {
    auto operand0 = getConstantValue(inst->getOperand(0));
    auto operand1 = getConstantValue(inst->getOperand(1));
    if (!operand0.isConstant())
      return operand0;
    if (!operand1.isConstant())
      return operand1;

    auto constFoldIntCompare =
        [&](const std::function<bool(const APInt &, const APInt &)> &fn)
        -> SymbolicValue {
      if (operand0.getKind() != SymbolicValue::Integer ||
          operand1.getKind() != SymbolicValue::Integer)
        return unknownResult();

      auto result = fn(operand0.getIntegerValue(), operand1.getIntegerValue());
      return SymbolicValue::getInteger(APInt(1, result),
                                       evaluator.getASTContext());
    };

#define REQUIRE_KIND(KIND)                                                     \
  if (operand0.getKind() != SymbolicValue::KIND ||                             \
      operand1.getKind() != SymbolicValue::KIND)                               \
    return unknownResult();

    switch (builtin.ID) {
    default:
      break;
#define INT_BINOP(OPCODE, EXPR)                                                \
  case BuiltinValueKind::OPCODE: {                                             \
    REQUIRE_KIND(Integer)                                                      \
    auto l = operand0.getIntegerValue(), r = operand1.getIntegerValue();       \
    return SymbolicValue::getInteger((EXPR), evaluator.getASTContext());       \
  }
      INT_BINOP(Add, l + r)
      INT_BINOP(And, l & r)
      INT_BINOP(AShr, l.ashr(r))
      INT_BINOP(LShr, l.lshr(r))
      INT_BINOP(Or, l | r)
      INT_BINOP(Mul, l * r)
      INT_BINOP(SDiv, l.sdiv(r))
      INT_BINOP(Shl, l << r)
      INT_BINOP(SRem, l.srem(r))
      INT_BINOP(Sub, l - r)
      INT_BINOP(UDiv, l.udiv(r))
      INT_BINOP(URem, l.urem(r))
      INT_BINOP(Xor, l ^ r)
#undef INT_BINOP

#define INT_COMPARE(OPCODE, EXPR)                                              \
  case BuiltinValueKind::OPCODE:                                               \
    REQUIRE_KIND(Integer)                                                      \
    return constFoldIntCompare(                                                \
        [&](const APInt &l, const APInt &r) -> bool { return (EXPR); })
      INT_COMPARE(ICMP_EQ, l == r);
      INT_COMPARE(ICMP_NE, l != r);
      INT_COMPARE(ICMP_SLT, l.slt(r));
      INT_COMPARE(ICMP_SGT, l.sgt(r));
      INT_COMPARE(ICMP_SLE, l.sle(r));
      INT_COMPARE(ICMP_SGE, l.sge(r));
      INT_COMPARE(ICMP_ULT, l.ult(r));
      INT_COMPARE(ICMP_UGT, l.ugt(r));
      INT_COMPARE(ICMP_ULE, l.ule(r));
      INT_COMPARE(ICMP_UGE, l.uge(r));
#undef INT_COMPARE
#undef REQUIRE_KIND
    }
  }

  // Three operand builtins.
  if (inst->getNumOperands() == 3) {
    auto operand0 = getConstantValue(inst->getOperand(0));
    auto operand1 = getConstantValue(inst->getOperand(1));
    auto operand2 = getConstantValue(inst->getOperand(2));
    if (!operand0.isConstant())
      return operand0;
    if (!operand1.isConstant())
      return operand1;
    if (!operand2.isConstant())
      return operand2;

    // Overflowing integer operations like sadd_with_overflow take three
    // operands: the last one is a "should report overflow" bit.
    auto constFoldIntOverflow =
        [&](const std::function<APInt(const APInt &, const APInt &, bool &)>
                &fn) -> SymbolicValue {
      if (operand0.getKind() != SymbolicValue::Integer ||
          operand1.getKind() != SymbolicValue::Integer ||
          operand2.getKind() != SymbolicValue::Integer)
        return unknownResult();

      auto l = operand0.getIntegerValue(), r = operand1.getIntegerValue();
      bool overflowed = false;
      auto result = fn(l, r, overflowed);

      // Return a statically diagnosed overflow if the operation is supposed to
      // trap on overflow.
      if (overflowed && !operand2.getIntegerValue().isNullValue())
        return evaluator.getUnknown(SILValue(inst), UnknownReason::Overflow);

      auto &astContext = evaluator.getASTContext();
      // Build the Symbolic value result for our normal and overflow bit.
      return SymbolicValue::getAggregate(
          {SymbolicValue::getInteger(result, astContext),
           SymbolicValue::getInteger(APInt(1, overflowed), astContext)},
          astContext);
    };

    switch (builtin.ID) {
    default:
      break;

#define INT_OVERFLOW(OPCODE, METHOD)                                           \
  case BuiltinValueKind::OPCODE:                                               \
    return constFoldIntOverflow(                                               \
        [&](const APInt &l, const APInt &r, bool &overflowed) -> APInt {       \
          return l.METHOD(r, overflowed);                                      \
        })
      INT_OVERFLOW(SAddOver, sadd_ov);
      INT_OVERFLOW(UAddOver, uadd_ov);
      INT_OVERFLOW(SSubOver, ssub_ov);
      INT_OVERFLOW(USubOver, usub_ov);
      INT_OVERFLOW(SMulOver, smul_ov);
      INT_OVERFLOW(UMulOver, umul_ov);
#undef INT_OVERFLOW
    }
  }

  LLVM_DEBUG(llvm::dbgs() << "ConstExpr Unknown Builtin: " << *inst << "\n");

  // Otherwise, we don't know how to handle this builtin.
  return unknownResult();
}
static SILInstruction *
constantFoldAndCheckIntegerConversions(BuiltinInst *BI,
                                       const BuiltinInfo &Builtin,
                                       Optional<bool> &ResultsInError) {
  assert(Builtin.ID == BuiltinValueKind::SToSCheckedTrunc ||
         Builtin.ID == BuiltinValueKind::UToUCheckedTrunc ||
         Builtin.ID == BuiltinValueKind::SToUCheckedTrunc ||
         Builtin.ID == BuiltinValueKind::UToSCheckedTrunc ||
         Builtin.ID == BuiltinValueKind::SUCheckedConversion ||
         Builtin.ID == BuiltinValueKind::USCheckedConversion);

  // Check if we are converting a constant integer.
  OperandValueArrayRef Args = BI->getArguments();
  auto *V = dyn_cast<IntegerLiteralInst>(Args[0]);
  if (!V)
    return nullptr;
  APInt SrcVal = V->getValue();

  // Get source type and bit width.
  Type SrcTy = Builtin.Types[0];
  uint32_t SrcBitWidth =
    Builtin.Types[0]->castTo<BuiltinIntegerType>()->getGreatestWidth();

  // Compute the destination (for SrcBitWidth < DestBitWidth) and enough info
  // to check for overflow.
  APInt Result;
  bool OverflowError;
  Type DstTy;

  // Process conversions signed <-> unsigned for same size integers.
  if (Builtin.ID == BuiltinValueKind::SUCheckedConversion ||
      Builtin.ID == BuiltinValueKind::USCheckedConversion) {
    DstTy = SrcTy;
    Result = SrcVal;
    // Report an error if the sign bit is set.
    OverflowError = SrcVal.isNegative();

  // Process truncation from unsigned to signed.
  } else if (Builtin.ID != BuiltinValueKind::UToSCheckedTrunc) {
    assert(Builtin.Types.size() == 2);
    DstTy = Builtin.Types[1];
    uint32_t DstBitWidth =
      DstTy->castTo<BuiltinIntegerType>()->getGreatestWidth();
    //     Result = trunc_IntFrom_IntTo(Val)
    //   For signed destination:
    //     sext_IntFrom(Result) == Val ? Result : overflow_error
    //   For signed destination:
    //     zext_IntFrom(Result) == Val ? Result : overflow_error
    Result = SrcVal.trunc(DstBitWidth);
    // Get the signedness of the destination.
    bool Signed = (Builtin.ID == BuiltinValueKind::SToSCheckedTrunc);
    APInt Ext = Signed ? Result.sext(SrcBitWidth) : Result.zext(SrcBitWidth);
    OverflowError = (SrcVal != Ext);

  // Process the rest of truncations.
  } else {
    assert(Builtin.Types.size() == 2);
    DstTy = Builtin.Types[1];
    uint32_t DstBitWidth =
      Builtin.Types[1]->castTo<BuiltinIntegerType>()->getGreatestWidth();
    // Compute the destination (for SrcBitWidth < DestBitWidth):
    //   Result = trunc_IntTo(Val)
    //   Trunc  = trunc_'IntTo-1bit'(Val)
    //   zext_IntFrom(Trunc) == Val ? Result : overflow_error
    Result = SrcVal.trunc(DstBitWidth);
    APInt TruncVal = SrcVal.trunc(DstBitWidth - 1);
    OverflowError = (SrcVal != TruncVal.zext(SrcBitWidth));
  }

  // Check for overflow.
  if (OverflowError) {
    // If we are not asked to emit overflow diagnostics, just return nullptr on
    // overflow.
    if (!ResultsInError.hasValue())
      return nullptr;

    SILLocation Loc = BI->getLoc();
    SILModule &M = BI->getModule();
    const ApplyExpr *CE = Loc.getAsASTNode<ApplyExpr>();
    Type UserSrcTy;
    Type UserDstTy;
    // Primitive heuristics to get the user-written type.
    // Eventually we might be able to use SILLocation (when it contains info
    // about inlined call chains).
    if (CE) {
      if (const TupleType *RTy = CE->getArg()->getType()->getAs<TupleType>()) {
        if (RTy->getNumElements() == 1) {
          UserSrcTy = RTy->getElementType(0);
          UserDstTy = CE->getType();
        }
      } else {
        UserSrcTy = CE->getArg()->getType();
        UserDstTy = CE->getType();
      }
    }
    
 
    // Assume that we are converting from a literal if the Source size is
    // 2048. Is there a better way to identify conversions from literals?
    bool Literal = (SrcBitWidth == 2048);

    // FIXME: This will prevent hard error in cases the error is coming
    // from ObjC interoperability code. Currently, we treat NSUInteger as
    // Int.
    if (Loc.getSourceLoc().isInvalid()) {
      // Otherwise emit the appropriate diagnostic and set ResultsInError.
      if (Literal)
        diagnose(M.getASTContext(), Loc.getSourceLoc(),
                 diag::integer_literal_overflow_warn,
                 UserDstTy.isNull() ? DstTy : UserDstTy);
      else
        diagnose(M.getASTContext(), Loc.getSourceLoc(),
                 diag::integer_conversion_overflow_warn,
                 UserSrcTy.isNull() ? SrcTy : UserSrcTy,
                 UserDstTy.isNull() ? DstTy : UserDstTy);

      ResultsInError = Optional<bool>(true);
      return nullptr;
    }

    // Otherwise report the overflow error.
    if (Literal) {
      bool SrcTySigned, DstTySigned;
      std::tie(SrcTySigned, DstTySigned) = getTypeSignedness(Builtin);
      SmallString<10> SrcAsString;
      SrcVal.toString(SrcAsString, /*radix*/10, SrcTySigned);

      // Try to print user-visible types if they are available.
      if (!UserDstTy.isNull()) {
        auto diagID = diag::integer_literal_overflow;
        
        // If this is a negative literal in an unsigned type, use a specific
        // diagnostic.
        if (SrcTySigned && !DstTySigned && SrcVal.isNegative())
          diagID = diag::negative_integer_literal_overflow_unsigned;
        
        diagnose(M.getASTContext(), Loc.getSourceLoc(),
                 diagID, UserDstTy, SrcAsString);
      // Otherwise, print the Builtin Types.
      } else {
        bool SrcTySigned, DstTySigned;
        std::tie(SrcTySigned, DstTySigned) = getTypeSignedness(Builtin);
        diagnose(M.getASTContext(), Loc.getSourceLoc(),
                 diag::integer_literal_overflow_builtin_types,
                 DstTySigned, DstTy, SrcAsString);
      }
    } else {
      if (Builtin.ID == BuiltinValueKind::SUCheckedConversion) {
        diagnose(M.getASTContext(), Loc.getSourceLoc(),
                 diag::integer_conversion_sign_error,
                 UserDstTy.isNull() ? DstTy : UserDstTy);
      } else {
        // Try to print user-visible types if they are available.
        if (!UserSrcTy.isNull()) {
          diagnose(M.getASTContext(), Loc.getSourceLoc(),
                   diag::integer_conversion_overflow,
                   UserSrcTy, UserDstTy);

        // Otherwise, print the Builtin Types.
        } else {
          // Since builtin types are sign-agnostic, print the signedness
          // separately.
          bool SrcTySigned, DstTySigned;
          std::tie(SrcTySigned, DstTySigned) = getTypeSignedness(Builtin);
          diagnose(M.getASTContext(), Loc.getSourceLoc(),
                   diag::integer_conversion_overflow_builtin_types,
                   SrcTySigned, SrcTy, DstTySigned, DstTy);
        }
      }
    }

    ResultsInError = Optional<bool>(true);
    return nullptr;
  }

  // The call to the builtin should be replaced with the constant value.
  return constructResultWithOverflowTuple(BI, Result, false);

}