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-rw-r--r--lib/Analysis/ValueTracking.cpp276
1 files changed, 159 insertions, 117 deletions
diff --git a/lib/Analysis/ValueTracking.cpp b/lib/Analysis/ValueTracking.cpp
index a7f3ff672aefc..cba7363a0afab 100644
--- a/lib/Analysis/ValueTracking.cpp
+++ b/lib/Analysis/ValueTracking.cpp
@@ -88,9 +88,8 @@ struct Query {
/// classic case of this is assume(x = y), which will attempt to determine
/// bits in x from bits in y, which will attempt to determine bits in y from
/// bits in x, etc. Regarding the mutual recursion, computeKnownBits can call
- /// isKnownNonZero, which calls computeKnownBits and ComputeSignBit and
- /// isKnownToBeAPowerOfTwo (all of which can call computeKnownBits), and so
- /// on.
+ /// isKnownNonZero, which calls computeKnownBits and isKnownToBeAPowerOfTwo
+ /// (all of which can call computeKnownBits), and so on.
std::array<const Value *, MaxDepth> Excluded;
unsigned NumExcluded;
@@ -143,6 +142,16 @@ void llvm::computeKnownBits(const Value *V, KnownBits &Known,
Query(DL, AC, safeCxtI(V, CxtI), DT, ORE));
}
+static KnownBits computeKnownBits(const Value *V, unsigned Depth,
+ const Query &Q);
+
+KnownBits llvm::computeKnownBits(const Value *V, const DataLayout &DL,
+ unsigned Depth, AssumptionCache *AC,
+ const Instruction *CxtI,
+ const DominatorTree *DT) {
+ return ::computeKnownBits(V, Depth, Query(DL, AC, safeCxtI(V, CxtI), DT));
+}
+
bool llvm::haveNoCommonBitsSet(const Value *LHS, const Value *RHS,
const DataLayout &DL,
AssumptionCache *AC, const Instruction *CxtI,
@@ -159,16 +168,6 @@ bool llvm::haveNoCommonBitsSet(const Value *LHS, const Value *RHS,
return (LHSKnown.Zero | RHSKnown.Zero).isAllOnesValue();
}
-static void ComputeSignBit(const Value *V, bool &KnownZero, bool &KnownOne,
- unsigned Depth, const Query &Q);
-
-void llvm::ComputeSignBit(const Value *V, bool &KnownZero, bool &KnownOne,
- const DataLayout &DL, unsigned Depth,
- AssumptionCache *AC, const Instruction *CxtI,
- const DominatorTree *DT) {
- ::ComputeSignBit(V, KnownZero, KnownOne, Depth,
- Query(DL, AC, safeCxtI(V, CxtI), DT));
-}
static bool isKnownToBeAPowerOfTwo(const Value *V, bool OrZero, unsigned Depth,
const Query &Q);
@@ -194,9 +193,8 @@ bool llvm::isKnownNonNegative(const Value *V, const DataLayout &DL,
unsigned Depth,
AssumptionCache *AC, const Instruction *CxtI,
const DominatorTree *DT) {
- bool NonNegative, Negative;
- ComputeSignBit(V, NonNegative, Negative, DL, Depth, AC, CxtI, DT);
- return NonNegative;
+ KnownBits Known = computeKnownBits(V, DL, Depth, AC, CxtI, DT);
+ return Known.isNonNegative();
}
bool llvm::isKnownPositive(const Value *V, const DataLayout &DL, unsigned Depth,
@@ -214,9 +212,8 @@ bool llvm::isKnownPositive(const Value *V, const DataLayout &DL, unsigned Depth,
bool llvm::isKnownNegative(const Value *V, const DataLayout &DL, unsigned Depth,
AssumptionCache *AC, const Instruction *CxtI,
const DominatorTree *DT) {
- bool NonNegative, Negative;
- ComputeSignBit(V, NonNegative, Negative, DL, Depth, AC, CxtI, DT);
- return Negative;
+ KnownBits Known = computeKnownBits(V, DL, Depth, AC, CxtI, DT);
+ return Known.isNegative();
}
static bool isKnownNonEqual(const Value *V1, const Value *V2, const Query &Q);
@@ -342,10 +339,10 @@ static void computeKnownBitsMul(const Value *Op0, const Value *Op1, bool NSW,
// Also compute a conservative estimate for high known-0 bits.
// More trickiness is possible, but this is sufficient for the
// interesting case of alignment computation.
- unsigned TrailZ = Known.Zero.countTrailingOnes() +
- Known2.Zero.countTrailingOnes();
- unsigned LeadZ = std::max(Known.Zero.countLeadingOnes() +
- Known2.Zero.countLeadingOnes(),
+ unsigned TrailZ = Known.countMinTrailingZeros() +
+ Known2.countMinTrailingZeros();
+ unsigned LeadZ = std::max(Known.countMinLeadingZeros() +
+ Known2.countMinLeadingZeros(),
BitWidth) - BitWidth;
TrailZ = std::min(TrailZ, BitWidth);
@@ -750,8 +747,8 @@ static void computeKnownBitsFromAssume(const Value *V, KnownBits &Known,
computeKnownBits(A, RHSKnown, Depth+1, Query(Q, I));
// Whatever high bits in c are zero are known to be zero.
- Known.Zero.setHighBits(RHSKnown.Zero.countLeadingOnes());
- // assume(v <_u c)
+ Known.Zero.setHighBits(RHSKnown.countMinLeadingZeros());
+ // assume(v <_u c)
} else if (match(Arg, m_ICmp(Pred, m_V, m_Value(A))) &&
Pred == ICmpInst::ICMP_ULT &&
isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
@@ -761,9 +758,9 @@ static void computeKnownBitsFromAssume(const Value *V, KnownBits &Known,
// Whatever high bits in c are zero are known to be zero (if c is a power
// of 2, then one more).
if (isKnownToBeAPowerOfTwo(A, false, Depth + 1, Query(Q, I)))
- Known.Zero.setHighBits(RHSKnown.Zero.countLeadingOnes()+1);
+ Known.Zero.setHighBits(RHSKnown.countMinLeadingZeros() + 1);
else
- Known.Zero.setHighBits(RHSKnown.Zero.countLeadingOnes());
+ Known.Zero.setHighBits(RHSKnown.countMinLeadingZeros());
}
}
@@ -916,7 +913,7 @@ static void computeKnownBitsFromOperator(const Operator *I, KnownBits &Known,
m_Value(Y))))) {
Known2.resetAll();
computeKnownBits(Y, Known2, Depth + 1, Q);
- if (Known2.One.countTrailingOnes() > 0)
+ if (Known2.countMinTrailingOnes() > 0)
Known.Zero.setBit(0);
}
break;
@@ -953,14 +950,13 @@ static void computeKnownBitsFromOperator(const Operator *I, KnownBits &Known,
// treat a udiv as a logical right shift by the power of 2 known to
// be less than the denominator.
computeKnownBits(I->getOperand(0), Known2, Depth + 1, Q);
- unsigned LeadZ = Known2.Zero.countLeadingOnes();
+ unsigned LeadZ = Known2.countMinLeadingZeros();
Known2.resetAll();
computeKnownBits(I->getOperand(1), Known2, Depth + 1, Q);
- unsigned RHSUnknownLeadingOnes = Known2.One.countLeadingZeros();
- if (RHSUnknownLeadingOnes != BitWidth)
- LeadZ = std::min(BitWidth,
- LeadZ + BitWidth - RHSUnknownLeadingOnes - 1);
+ unsigned RHSMaxLeadingZeros = Known2.countMaxLeadingZeros();
+ if (RHSMaxLeadingZeros != BitWidth)
+ LeadZ = std::min(BitWidth, LeadZ + BitWidth - RHSMaxLeadingZeros - 1);
Known.Zero.setHighBits(LeadZ);
break;
@@ -983,8 +979,8 @@ static void computeKnownBitsFromOperator(const Operator *I, KnownBits &Known,
if (Known.isNegative() && Known2.isNegative())
// We can derive a lower bound on the result by taking the max of the
// leading one bits.
- MaxHighOnes = std::max(Known.One.countLeadingOnes(),
- Known2.One.countLeadingOnes());
+ MaxHighOnes =
+ std::max(Known.countMinLeadingOnes(), Known2.countMinLeadingOnes());
// If either side is non-negative, the result is non-negative.
else if (Known.isNonNegative() || Known2.isNonNegative())
MaxHighZeros = 1;
@@ -993,8 +989,8 @@ static void computeKnownBitsFromOperator(const Operator *I, KnownBits &Known,
if (Known.isNonNegative() && Known2.isNonNegative())
// We can derive an upper bound on the result by taking the max of the
// leading zero bits.
- MaxHighZeros = std::max(Known.Zero.countLeadingOnes(),
- Known2.Zero.countLeadingOnes());
+ MaxHighZeros = std::max(Known.countMinLeadingZeros(),
+ Known2.countMinLeadingZeros());
// If either side is negative, the result is negative.
else if (Known.isNegative() || Known2.isNegative())
MaxHighOnes = 1;
@@ -1002,12 +998,12 @@ static void computeKnownBitsFromOperator(const Operator *I, KnownBits &Known,
// We can derive a lower bound on the result by taking the max of the
// leading one bits.
MaxHighOnes =
- std::max(Known.One.countLeadingOnes(), Known2.One.countLeadingOnes());
+ std::max(Known.countMinLeadingOnes(), Known2.countMinLeadingOnes());
} else if (SPF == SPF_UMIN) {
// We can derive an upper bound on the result by taking the max of the
// leading zero bits.
MaxHighZeros =
- std::max(Known.Zero.countLeadingOnes(), Known2.Zero.countLeadingOnes());
+ std::max(Known.countMinLeadingZeros(), Known2.countMinLeadingZeros());
}
// Only known if known in both the LHS and RHS.
@@ -1185,8 +1181,8 @@ static void computeKnownBitsFromOperator(const Operator *I, KnownBits &Known,
computeKnownBits(I->getOperand(0), Known, Depth + 1, Q);
computeKnownBits(I->getOperand(1), Known2, Depth + 1, Q);
- unsigned Leaders = std::max(Known.Zero.countLeadingOnes(),
- Known2.Zero.countLeadingOnes());
+ unsigned Leaders =
+ std::max(Known.countMinLeadingZeros(), Known2.countMinLeadingZeros());
Known.resetAll();
Known.Zero.setHighBits(Leaders);
break;
@@ -1207,7 +1203,7 @@ static void computeKnownBitsFromOperator(const Operator *I, KnownBits &Known,
// to determine if we can prove known low zero bits.
KnownBits LocalKnown(BitWidth);
computeKnownBits(I->getOperand(0), LocalKnown, Depth + 1, Q);
- unsigned TrailZ = LocalKnown.Zero.countTrailingOnes();
+ unsigned TrailZ = LocalKnown.countMinTrailingZeros();
gep_type_iterator GTI = gep_type_begin(I);
for (unsigned i = 1, e = I->getNumOperands(); i != e; ++i, ++GTI) {
@@ -1241,7 +1237,7 @@ static void computeKnownBitsFromOperator(const Operator *I, KnownBits &Known,
computeKnownBits(Index, LocalKnown, Depth + 1, Q);
TrailZ = std::min(TrailZ,
unsigned(countTrailingZeros(TypeSize) +
- LocalKnown.Zero.countTrailingOnes()));
+ LocalKnown.countMinTrailingZeros()));
}
}
@@ -1286,8 +1282,8 @@ static void computeKnownBitsFromOperator(const Operator *I, KnownBits &Known,
KnownBits Known3(Known);
computeKnownBits(L, Known3, Depth + 1, Q);
- Known.Zero.setLowBits(std::min(Known2.Zero.countTrailingOnes(),
- Known3.Zero.countTrailingOnes()));
+ Known.Zero.setLowBits(std::min(Known2.countMinTrailingZeros(),
+ Known3.countMinTrailingZeros()));
if (DontImproveNonNegativePhiBits)
break;
@@ -1386,12 +1382,25 @@ static void computeKnownBitsFromOperator(const Operator *I, KnownBits &Known,
Known.Zero |= Known2.Zero.byteSwap();
Known.One |= Known2.One.byteSwap();
break;
- case Intrinsic::ctlz:
+ case Intrinsic::ctlz: {
+ computeKnownBits(I->getOperand(0), Known2, Depth + 1, Q);
+ // If we have a known 1, its position is our upper bound.
+ unsigned PossibleLZ = Known2.One.countLeadingZeros();
+ // If this call is undefined for 0, the result will be less than 2^n.
+ if (II->getArgOperand(1) == ConstantInt::getTrue(II->getContext()))
+ PossibleLZ = std::min(PossibleLZ, BitWidth - 1);
+ unsigned LowBits = Log2_32(PossibleLZ)+1;
+ Known.Zero.setBitsFrom(LowBits);
+ break;
+ }
case Intrinsic::cttz: {
- unsigned LowBits = Log2_32(BitWidth)+1;
+ computeKnownBits(I->getOperand(0), Known2, Depth + 1, Q);
+ // If we have a known 1, its position is our upper bound.
+ unsigned PossibleTZ = Known2.One.countTrailingZeros();
// If this call is undefined for 0, the result will be less than 2^n.
if (II->getArgOperand(1) == ConstantInt::getTrue(II->getContext()))
- LowBits -= 1;
+ PossibleTZ = std::min(PossibleTZ, BitWidth - 1);
+ unsigned LowBits = Log2_32(PossibleTZ)+1;
Known.Zero.setBitsFrom(LowBits);
break;
}
@@ -1399,7 +1408,7 @@ static void computeKnownBitsFromOperator(const Operator *I, KnownBits &Known,
computeKnownBits(I->getOperand(0), Known2, Depth + 1, Q);
// We can bound the space the count needs. Also, bits known to be zero
// can't contribute to the population.
- unsigned BitsPossiblySet = BitWidth - Known2.Zero.countPopulation();
+ unsigned BitsPossiblySet = Known2.countMaxPopulation();
unsigned LowBits = Log2_32(BitsPossiblySet)+1;
Known.Zero.setBitsFrom(LowBits);
// TODO: we could bound KnownOne using the lower bound on the number
@@ -1450,6 +1459,14 @@ static void computeKnownBitsFromOperator(const Operator *I, KnownBits &Known,
}
/// Determine which bits of V are known to be either zero or one and return
+/// them.
+KnownBits computeKnownBits(const Value *V, unsigned Depth, const Query &Q) {
+ KnownBits Known(getBitWidth(V->getType(), Q.DL));
+ computeKnownBits(V, Known, Depth, Q);
+ return Known;
+}
+
+/// Determine which bits of V are known to be either zero or one and return
/// them in the Known bit set.
///
/// NOTE: we cannot consider 'undef' to be "IsZero" here. The problem is that
@@ -1568,16 +1585,6 @@ void computeKnownBits(const Value *V, KnownBits &Known, unsigned Depth,
assert((Known.Zero & Known.One) == 0 && "Bits known to be one AND zero?");
}
-/// Determine whether the sign bit is known to be zero or one.
-/// Convenience wrapper around computeKnownBits.
-void ComputeSignBit(const Value *V, bool &KnownZero, bool &KnownOne,
- unsigned Depth, const Query &Q) {
- KnownBits Bits(getBitWidth(V->getType(), Q.DL));
- computeKnownBits(V, Bits, Depth, Q);
- KnownOne = Bits.isNegative();
- KnownZero = Bits.isNonNegative();
-}
-
/// Return true if the given value is known to have exactly one
/// bit set when defined. For vectors return true if every element is known to
/// be a power of two when defined. Supports values with integer or pointer
@@ -1842,24 +1849,20 @@ bool isKnownNonZero(const Value *V, unsigned Depth, const Query &Q) {
if (BO->isExact())
return isKnownNonZero(X, Depth, Q);
- bool XKnownNonNegative, XKnownNegative;
- ComputeSignBit(X, XKnownNonNegative, XKnownNegative, Depth, Q);
- if (XKnownNegative)
+ KnownBits Known = computeKnownBits(X, Depth, Q);
+ if (Known.isNegative())
return true;
// If the shifter operand is a constant, and all of the bits shifted
// out are known to be zero, and X is known non-zero then at least one
// non-zero bit must remain.
if (ConstantInt *Shift = dyn_cast<ConstantInt>(Y)) {
- KnownBits Known(BitWidth);
- computeKnownBits(X, Known, Depth, Q);
-
auto ShiftVal = Shift->getLimitedValue(BitWidth - 1);
// Is there a known one in the portion not shifted out?
- if (Known.One.countLeadingZeros() < BitWidth - ShiftVal)
+ if (Known.countMaxLeadingZeros() < BitWidth - ShiftVal)
return true;
// Are all the bits to be shifted out known zero?
- if (Known.Zero.countTrailingOnes() >= ShiftVal)
+ if (Known.countMinTrailingZeros() >= ShiftVal)
return isKnownNonZero(X, Depth, Q);
}
}
@@ -1869,39 +1872,34 @@ bool isKnownNonZero(const Value *V, unsigned Depth, const Query &Q) {
}
// X + Y.
else if (match(V, m_Add(m_Value(X), m_Value(Y)))) {
- bool XKnownNonNegative, XKnownNegative;
- bool YKnownNonNegative, YKnownNegative;
- ComputeSignBit(X, XKnownNonNegative, XKnownNegative, Depth, Q);
- ComputeSignBit(Y, YKnownNonNegative, YKnownNegative, Depth, Q);
+ KnownBits XKnown = computeKnownBits(X, Depth, Q);
+ KnownBits YKnown = computeKnownBits(Y, Depth, Q);
// If X and Y are both non-negative (as signed values) then their sum is not
// zero unless both X and Y are zero.
- if (XKnownNonNegative && YKnownNonNegative)
+ if (XKnown.isNonNegative() && YKnown.isNonNegative())
if (isKnownNonZero(X, Depth, Q) || isKnownNonZero(Y, Depth, Q))
return true;
// If X and Y are both negative (as signed values) then their sum is not
// zero unless both X and Y equal INT_MIN.
- if (XKnownNegative && YKnownNegative) {
- KnownBits Known(BitWidth);
+ if (XKnown.isNegative() && YKnown.isNegative()) {
APInt Mask = APInt::getSignedMaxValue(BitWidth);
// The sign bit of X is set. If some other bit is set then X is not equal
// to INT_MIN.
- computeKnownBits(X, Known, Depth, Q);
- if (Known.One.intersects(Mask))
+ if (XKnown.One.intersects(Mask))
return true;
// The sign bit of Y is set. If some other bit is set then Y is not equal
// to INT_MIN.
- computeKnownBits(Y, Known, Depth, Q);
- if (Known.One.intersects(Mask))
+ if (YKnown.One.intersects(Mask))
return true;
}
// The sum of a non-negative number and a power of two is not zero.
- if (XKnownNonNegative &&
+ if (XKnown.isNonNegative() &&
isKnownToBeAPowerOfTwo(Y, /*OrZero*/ false, Depth, Q))
return true;
- if (YKnownNonNegative &&
+ if (YKnown.isNonNegative() &&
isKnownToBeAPowerOfTwo(X, /*OrZero*/ false, Depth, Q))
return true;
}
@@ -2276,14 +2274,7 @@ static unsigned ComputeNumSignBitsImpl(const Value *V, unsigned Depth,
// If we know that the sign bit is either zero or one, determine the number of
// identical bits in the top of the input value.
- if (Known.isNonNegative())
- return std::max(FirstAnswer, Known.Zero.countLeadingOnes());
-
- if (Known.isNegative())
- return std::max(FirstAnswer, Known.One.countLeadingOnes());
-
- // computeKnownBits gave us no extra information about the top bits.
- return FirstAnswer;
+ return std::max(FirstAnswer, Known.countMinSignBits());
}
/// This function computes the integer multiple of Base that equals V.
@@ -3441,8 +3432,8 @@ OverflowResult llvm::computeOverflowForUnsignedMul(const Value *LHS,
computeKnownBits(RHS, RHSKnown, DL, /*Depth=*/0, AC, CxtI, DT);
// Note that underestimating the number of zero bits gives a more
// conservative answer.
- unsigned ZeroBits = LHSKnown.Zero.countLeadingOnes() +
- RHSKnown.Zero.countLeadingOnes();
+ unsigned ZeroBits = LHSKnown.countMinLeadingZeros() +
+ RHSKnown.countMinLeadingZeros();
// First handle the easy case: if we have enough zero bits there's
// definitely no overflow.
if (ZeroBits >= BitWidth)
@@ -3475,21 +3466,17 @@ OverflowResult llvm::computeOverflowForUnsignedAdd(const Value *LHS,
AssumptionCache *AC,
const Instruction *CxtI,
const DominatorTree *DT) {
- bool LHSKnownNonNegative, LHSKnownNegative;
- ComputeSignBit(LHS, LHSKnownNonNegative, LHSKnownNegative, DL, /*Depth=*/0,
- AC, CxtI, DT);
- if (LHSKnownNonNegative || LHSKnownNegative) {
- bool RHSKnownNonNegative, RHSKnownNegative;
- ComputeSignBit(RHS, RHSKnownNonNegative, RHSKnownNegative, DL, /*Depth=*/0,
- AC, CxtI, DT);
-
- if (LHSKnownNegative && RHSKnownNegative) {
+ KnownBits LHSKnown = computeKnownBits(LHS, DL, /*Depth=*/0, AC, CxtI, DT);
+ if (LHSKnown.isNonNegative() || LHSKnown.isNegative()) {
+ KnownBits RHSKnown = computeKnownBits(RHS, DL, /*Depth=*/0, AC, CxtI, DT);
+
+ if (LHSKnown.isNegative() && RHSKnown.isNegative()) {
// The sign bit is set in both cases: this MUST overflow.
// Create a simple add instruction, and insert it into the struct.
return OverflowResult::AlwaysOverflows;
}
- if (LHSKnownNonNegative && RHSKnownNonNegative) {
+ if (LHSKnown.isNonNegative() && RHSKnown.isNonNegative()) {
// The sign bit is clear in both cases: this CANNOT overflow.
// Create a simple add instruction, and insert it into the struct.
return OverflowResult::NeverOverflows;
@@ -3499,6 +3486,51 @@ OverflowResult llvm::computeOverflowForUnsignedAdd(const Value *LHS,
return OverflowResult::MayOverflow;
}
+/// \brief Return true if we can prove that adding the two values of the
+/// knownbits will not overflow.
+/// Otherwise return false.
+static bool checkRippleForSignedAdd(const KnownBits &LHSKnown,
+ const KnownBits &RHSKnown) {
+ // Addition of two 2's complement numbers having opposite signs will never
+ // overflow.
+ if ((LHSKnown.isNegative() && RHSKnown.isNonNegative()) ||
+ (LHSKnown.isNonNegative() && RHSKnown.isNegative()))
+ return true;
+
+ // If either of the values is known to be non-negative, adding them can only
+ // overflow if the second is also non-negative, so we can assume that.
+ // Two non-negative numbers will only overflow if there is a carry to the
+ // sign bit, so we can check if even when the values are as big as possible
+ // there is no overflow to the sign bit.
+ if (LHSKnown.isNonNegative() || RHSKnown.isNonNegative()) {
+ APInt MaxLHS = ~LHSKnown.Zero;
+ MaxLHS.clearSignBit();
+ APInt MaxRHS = ~RHSKnown.Zero;
+ MaxRHS.clearSignBit();
+ APInt Result = std::move(MaxLHS) + std::move(MaxRHS);
+ return Result.isSignBitClear();
+ }
+
+ // If either of the values is known to be negative, adding them can only
+ // overflow if the second is also negative, so we can assume that.
+ // Two negative number will only overflow if there is no carry to the sign
+ // bit, so we can check if even when the values are as small as possible
+ // there is overflow to the sign bit.
+ if (LHSKnown.isNegative() || RHSKnown.isNegative()) {
+ APInt MinLHS = LHSKnown.One;
+ MinLHS.clearSignBit();
+ APInt MinRHS = RHSKnown.One;
+ MinRHS.clearSignBit();
+ APInt Result = std::move(MinLHS) + std::move(MinRHS);
+ return Result.isSignBitSet();
+ }
+
+ // If we reached here it means that we know nothing about the sign bits.
+ // In this case we can't know if there will be an overflow, since by
+ // changing the sign bits any two values can be made to overflow.
+ return false;
+}
+
static OverflowResult computeOverflowForSignedAdd(const Value *LHS,
const Value *RHS,
const AddOperator *Add,
@@ -3510,18 +3542,29 @@ static OverflowResult computeOverflowForSignedAdd(const Value *LHS,
return OverflowResult::NeverOverflows;
}
- bool LHSKnownNonNegative, LHSKnownNegative;
- bool RHSKnownNonNegative, RHSKnownNegative;
- ComputeSignBit(LHS, LHSKnownNonNegative, LHSKnownNegative, DL, /*Depth=*/0,
- AC, CxtI, DT);
- ComputeSignBit(RHS, RHSKnownNonNegative, RHSKnownNegative, DL, /*Depth=*/0,
- AC, CxtI, DT);
+ // If LHS and RHS each have at least two sign bits, the addition will look
+ // like
+ //
+ // XX..... +
+ // YY.....
+ //
+ // If the carry into the most significant position is 0, X and Y can't both
+ // be 1 and therefore the carry out of the addition is also 0.
+ //
+ // If the carry into the most significant position is 1, X and Y can't both
+ // be 0 and therefore the carry out of the addition is also 1.
+ //
+ // Since the carry into the most significant position is always equal to
+ // the carry out of the addition, there is no signed overflow.
+ if (ComputeNumSignBits(LHS, DL, 0, AC, CxtI, DT) > 1 &&
+ ComputeNumSignBits(RHS, DL, 0, AC, CxtI, DT) > 1)
+ return OverflowResult::NeverOverflows;
+
+ KnownBits LHSKnown = computeKnownBits(LHS, DL, /*Depth=*/0, AC, CxtI, DT);
+ KnownBits RHSKnown = computeKnownBits(RHS, DL, /*Depth=*/0, AC, CxtI, DT);
- if ((LHSKnownNonNegative && RHSKnownNegative) ||
- (LHSKnownNegative && RHSKnownNonNegative)) {
- // The sign bits are opposite: this CANNOT overflow.
+ if (checkRippleForSignedAdd(LHSKnown, RHSKnown))
return OverflowResult::NeverOverflows;
- }
// The remaining code needs Add to be available. Early returns if not so.
if (!Add)
@@ -3532,14 +3575,13 @@ static OverflowResult computeOverflowForSignedAdd(const Value *LHS,
// @llvm.assume'ed non-negative rather than proved so from analyzing its
// operands.
bool LHSOrRHSKnownNonNegative =
- (LHSKnownNonNegative || RHSKnownNonNegative);
- bool LHSOrRHSKnownNegative = (LHSKnownNegative || RHSKnownNegative);
+ (LHSKnown.isNonNegative() || RHSKnown.isNonNegative());
+ bool LHSOrRHSKnownNegative =
+ (LHSKnown.isNegative() || RHSKnown.isNegative());
if (LHSOrRHSKnownNonNegative || LHSOrRHSKnownNegative) {
- bool AddKnownNonNegative, AddKnownNegative;
- ComputeSignBit(Add, AddKnownNonNegative, AddKnownNegative, DL,
- /*Depth=*/0, AC, CxtI, DT);
- if ((AddKnownNonNegative && LHSOrRHSKnownNonNegative) ||
- (AddKnownNegative && LHSOrRHSKnownNegative)) {
+ KnownBits AddKnown = computeKnownBits(Add, DL, /*Depth=*/0, AC, CxtI, DT);
+ if ((AddKnown.isNonNegative() && LHSOrRHSKnownNonNegative) ||
+ (AddKnown.isNegative() && LHSOrRHSKnownNegative)) {
return OverflowResult::NeverOverflows;
}
}
generated by cgit v1.2.3 (git 2.25.1) at 2025-06-22 08:45:20 +0000