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llvm-6502/lib/Analysis/ValueTracking.cpp
Sanjay Patel d2c64e2df9 Fix really obscure bug in CannotBeNegativeZero() (PR22688) 
With a diabolically crafted test case, we could recurse
through this code and return true instead of false.

The larger engineering crime is the use of magic numbers. 
Added FIXME comments for those.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@230515 91177308-0d34-0410-b5e6-96231b3b80d8
2015-02-25 18:00:15 +00:00

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//===- ValueTracking.cpp - Walk computations to compute properties --------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file contains routines that help analyze properties that chains of
// computations have.
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/MemoryBuiltins.h"
#include "llvm/IR/CallSite.h"
#include "llvm/IR/ConstantRange.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/GetElementPtrTypeIterator.h"
#include "llvm/IR/GlobalAlias.h"
#include "llvm/IR/GlobalVariable.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Metadata.h"
#include "llvm/IR/Operator.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/MathExtras.h"
#include <cstring>
using namespace llvm;
using namespace llvm::PatternMatch;
const unsigned MaxDepth = 6;
/// Returns the bitwidth of the given scalar or pointer type (if unknown returns
/// 0). For vector types, returns the element type's bitwidth.
static unsigned getBitWidth(Type *Ty, const DataLayout *TD) {
if (unsigned BitWidth = Ty->getScalarSizeInBits())
return BitWidth;
return TD ? TD->getPointerTypeSizeInBits(Ty) : 0;
}
// Many of these functions have internal versions that take an assumption
// exclusion set. This is because of the potential for mutual recursion to
// cause computeKnownBits to repeatedly visit the same assume intrinsic. The
// 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.
typedef SmallPtrSet<const Value *, 8> ExclInvsSet;
namespace {
// Simplifying using an assume can only be done in a particular control-flow
// context (the context instruction provides that context). If an assume and
// the context instruction are not in the same block then the DT helps in
// figuring out if we can use it.
struct Query {
ExclInvsSet ExclInvs;
AssumptionCache *AC;
const Instruction *CxtI;
const DominatorTree *DT;
Query(AssumptionCache *AC = nullptr, const Instruction *CxtI = nullptr,
const DominatorTree *DT = nullptr)
: AC(AC), CxtI(CxtI), DT(DT) {}
Query(const Query &Q, const Value *NewExcl)
: ExclInvs(Q.ExclInvs), AC(Q.AC), CxtI(Q.CxtI), DT(Q.DT) {
ExclInvs.insert(NewExcl);
}
};
} // end anonymous namespace
// Given the provided Value and, potentially, a context instruction, return
// the preferred context instruction (if any).
static const Instruction *safeCxtI(const Value *V, const Instruction *CxtI) {
// If we've been provided with a context instruction, then use that (provided
// it has been inserted).
if (CxtI && CxtI->getParent())
return CxtI;
// If the value is really an already-inserted instruction, then use that.
CxtI = dyn_cast<Instruction>(V);
if (CxtI && CxtI->getParent())
return CxtI;
return nullptr;
}
static void computeKnownBits(Value *V, APInt &KnownZero, APInt &KnownOne,
const DataLayout *TD, unsigned Depth,
const Query &Q);
void llvm::computeKnownBits(Value *V, APInt &KnownZero, APInt &KnownOne,
const DataLayout *TD, unsigned Depth,
AssumptionCache *AC, const Instruction *CxtI,
const DominatorTree *DT) {
::computeKnownBits(V, KnownZero, KnownOne, TD, Depth,
Query(AC, safeCxtI(V, CxtI), DT));
}
static void ComputeSignBit(Value *V, bool &KnownZero, bool &KnownOne,
const DataLayout *TD, unsigned Depth,
const Query &Q);
void llvm::ComputeSignBit(Value *V, bool &KnownZero, bool &KnownOne,
const DataLayout *TD, unsigned Depth,
AssumptionCache *AC, const Instruction *CxtI,
const DominatorTree *DT) {
::ComputeSignBit(V, KnownZero, KnownOne, TD, Depth,
Query(AC, safeCxtI(V, CxtI), DT));
}
static bool isKnownToBeAPowerOfTwo(Value *V, bool OrZero, unsigned Depth,
const Query &Q);
bool llvm::isKnownToBeAPowerOfTwo(Value *V, bool OrZero, unsigned Depth,
AssumptionCache *AC, const Instruction *CxtI,
const DominatorTree *DT) {
return ::isKnownToBeAPowerOfTwo(V, OrZero, Depth,
Query(AC, safeCxtI(V, CxtI), DT));
}
static bool isKnownNonZero(Value *V, const DataLayout *TD, unsigned Depth,
const Query &Q);
bool llvm::isKnownNonZero(Value *V, const DataLayout *TD, unsigned Depth,
AssumptionCache *AC, const Instruction *CxtI,
const DominatorTree *DT) {
return ::isKnownNonZero(V, TD, Depth, Query(AC, safeCxtI(V, CxtI), DT));
}
static bool MaskedValueIsZero(Value *V, const APInt &Mask,
const DataLayout *TD, unsigned Depth,
const Query &Q);
bool llvm::MaskedValueIsZero(Value *V, const APInt &Mask, const DataLayout *TD,
unsigned Depth, AssumptionCache *AC,
const Instruction *CxtI, const DominatorTree *DT) {
return ::MaskedValueIsZero(V, Mask, TD, Depth,
Query(AC, safeCxtI(V, CxtI), DT));
}
static unsigned ComputeNumSignBits(Value *V, const DataLayout *TD,
unsigned Depth, const Query &Q);
unsigned llvm::ComputeNumSignBits(Value *V, const DataLayout *TD,
unsigned Depth, AssumptionCache *AC,
const Instruction *CxtI,
const DominatorTree *DT) {
return ::ComputeNumSignBits(V, TD, Depth, Query(AC, safeCxtI(V, CxtI), DT));
}
static void computeKnownBitsAddSub(bool Add, Value *Op0, Value *Op1, bool NSW,
APInt &KnownZero, APInt &KnownOne,
APInt &KnownZero2, APInt &KnownOne2,
const DataLayout *TD, unsigned Depth,
const Query &Q) {
if (!Add) {
if (ConstantInt *CLHS = dyn_cast<ConstantInt>(Op0)) {
// 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 BitWidth = KnownZero.getBitWidth();
unsigned NLZ = (CLHS->getValue()+1).countLeadingZeros();
// NLZ can't be BitWidth with no sign bit
APInt MaskV = APInt::getHighBitsSet(BitWidth, NLZ+1);
computeKnownBits(Op1, KnownZero2, KnownOne2, TD, Depth+1, Q);
// 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);
}
}
}
}
unsigned BitWidth = KnownZero.getBitWidth();
// If an initial sequence of bits in the result is not needed, the
// corresponding bits in the operands are not needed.
APInt LHSKnownZero(BitWidth, 0), LHSKnownOne(BitWidth, 0);
computeKnownBits(Op0, LHSKnownZero, LHSKnownOne, TD, Depth+1, Q);
computeKnownBits(Op1, KnownZero2, KnownOne2, TD, Depth+1, Q);
// Carry in a 1 for a subtract, rather than a 0.
APInt CarryIn(BitWidth, 0);
if (!Add) {
// Sum = LHS + ~RHS + 1
std::swap(KnownZero2, KnownOne2);
CarryIn.setBit(0);
}
APInt PossibleSumZero = ~LHSKnownZero + ~KnownZero2 + CarryIn;
APInt PossibleSumOne = LHSKnownOne + KnownOne2 + CarryIn;
// Compute known bits of the carry.
APInt CarryKnownZero = ~(PossibleSumZero ^ LHSKnownZero ^ KnownZero2);
APInt CarryKnownOne = PossibleSumOne ^ LHSKnownOne ^ KnownOne2;
// Compute set of known bits (where all three relevant bits are known).
APInt LHSKnown = LHSKnownZero | LHSKnownOne;
APInt RHSKnown = KnownZero2 | KnownOne2;
APInt CarryKnown = CarryKnownZero | CarryKnownOne;
APInt Known = LHSKnown & RHSKnown & CarryKnown;
assert((PossibleSumZero & Known) == (PossibleSumOne & Known) &&
"known bits of sum differ");
// Compute known bits of the result.
KnownZero = ~PossibleSumOne & Known;
KnownOne = PossibleSumOne & Known;
// Are we still trying to solve for the sign bit?
if (!Known.isNegative()) {
if (NSW) {
// Adding two non-negative numbers, or subtracting a negative number from
// a non-negative one, can't wrap into negative.
if (LHSKnownZero.isNegative() && KnownZero2.isNegative())
KnownZero |= APInt::getSignBit(BitWidth);
// Adding two negative numbers, or subtracting a non-negative number from
// a negative one, can't wrap into non-negative.
else if (LHSKnownOne.isNegative() && KnownOne2.isNegative())
KnownOne |= APInt::getSignBit(BitWidth);
}
}
}
static void computeKnownBitsMul(Value *Op0, Value *Op1, bool NSW,
APInt &KnownZero, APInt &KnownOne,
APInt &KnownZero2, APInt &KnownOne2,
const DataLayout *TD, unsigned Depth,
const Query &Q) {
unsigned BitWidth = KnownZero.getBitWidth();
computeKnownBits(Op1, KnownZero, KnownOne, TD, Depth+1, Q);
computeKnownBits(Op0, KnownZero2, KnownOne2, TD, Depth+1, Q);
bool isKnownNegative = false;
bool isKnownNonNegative = false;
// If the multiplication is known not to overflow, compute the sign bit.
if (NSW) {
if (Op0 == Op1) {
// The product of a number with itself is non-negative.
isKnownNonNegative = true;
} else {
bool isKnownNonNegativeOp1 = KnownZero.isNegative();
bool isKnownNonNegativeOp0 = KnownZero2.isNegative();
bool isKnownNegativeOp1 = KnownOne.isNegative();
bool isKnownNegativeOp0 = KnownOne2.isNegative();
// The product of two numbers with the same sign is non-negative.
isKnownNonNegative = (isKnownNegativeOp1 && isKnownNegativeOp0) ||
(isKnownNonNegativeOp1 && isKnownNonNegativeOp0);
// The product of a negative number and a non-negative number is either
// negative or zero.
if (!isKnownNonNegative)
isKnownNegative = (isKnownNegativeOp1 && isKnownNonNegativeOp0 &&
isKnownNonZero(Op0, TD, Depth, Q)) ||
(isKnownNegativeOp0 && isKnownNonNegativeOp1 &&
isKnownNonZero(Op1, TD, Depth, Q));
}
}
// 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.clearAllBits();
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);
// Only make use of no-wrap flags if we failed to compute the sign bit
// directly. This matters if the multiplication always overflows, in
// which case we prefer to follow the result of the direct computation,
// though as the program is invoking undefined behaviour we can choose
// whatever we like here.
if (isKnownNonNegative && !KnownOne.isNegative())
KnownZero.setBit(BitWidth - 1);
else if (isKnownNegative && !KnownZero.isNegative())
KnownOne.setBit(BitWidth - 1);
}
void llvm::computeKnownBitsFromRangeMetadata(const MDNode &Ranges,
APInt &KnownZero) {
unsigned BitWidth = KnownZero.getBitWidth();
unsigned NumRanges = Ranges.getNumOperands() / 2;
assert(NumRanges >= 1);
// Use the high end of the ranges to find leading zeros.
unsigned MinLeadingZeros = BitWidth;
for (unsigned i = 0; i < NumRanges; ++i) {
ConstantInt *Lower =
mdconst::extract<ConstantInt>(Ranges.getOperand(2 * i + 0));
ConstantInt *Upper =
mdconst::extract<ConstantInt>(Ranges.getOperand(2 * i + 1));
ConstantRange Range(Lower->getValue(), Upper->getValue());
if (Range.isWrappedSet())
MinLeadingZeros = 0; // -1 has no zeros
unsigned LeadingZeros = (Upper->getValue() - 1).countLeadingZeros();
MinLeadingZeros = std::min(LeadingZeros, MinLeadingZeros);
}
KnownZero = APInt::getHighBitsSet(BitWidth, MinLeadingZeros);
}
static bool isEphemeralValueOf(Instruction *I, const Value *E) {
SmallVector<const Value *, 16> WorkSet(1, I);
SmallPtrSet<const Value *, 32> Visited;
SmallPtrSet<const Value *, 16> EphValues;
while (!WorkSet.empty()) {
const Value *V = WorkSet.pop_back_val();
if (!Visited.insert(V).second)
continue;
// If all uses of this value are ephemeral, then so is this value.
bool FoundNEUse = false;
for (const User *I : V->users())
if (!EphValues.count(I)) {
FoundNEUse = true;
break;
}
if (!FoundNEUse) {
if (V == E)
return true;
EphValues.insert(V);
if (const User *U = dyn_cast<User>(V))
for (User::const_op_iterator J = U->op_begin(), JE = U->op_end();
J != JE; ++J) {
if (isSafeToSpeculativelyExecute(*J))
WorkSet.push_back(*J);
}
}
}
return false;
}
// Is this an intrinsic that cannot be speculated but also cannot trap?
static bool isAssumeLikeIntrinsic(const Instruction *I) {
if (const CallInst *CI = dyn_cast<CallInst>(I))
if (Function *F = CI->getCalledFunction())
switch (F->getIntrinsicID()) {
default: break;
// FIXME: This list is repeated from NoTTI::getIntrinsicCost.
case Intrinsic::assume:
case Intrinsic::dbg_declare:
case Intrinsic::dbg_value:
case Intrinsic::invariant_start:
case Intrinsic::invariant_end:
case Intrinsic::lifetime_start:
case Intrinsic::lifetime_end:
case Intrinsic::objectsize:
case Intrinsic::ptr_annotation:
case Intrinsic::var_annotation:
return true;
}
return false;
}
static bool isValidAssumeForContext(Value *V, const Query &Q,
const DataLayout *DL) {
Instruction *Inv = cast<Instruction>(V);
// There are two restrictions on the use of an assume:
// 1. The assume must dominate the context (or the control flow must
// reach the assume whenever it reaches the context).
// 2. The context must not be in the assume's set of ephemeral values
// (otherwise we will use the assume to prove that the condition
// feeding the assume is trivially true, thus causing the removal of
// the assume).
if (Q.DT) {
if (Q.DT->dominates(Inv, Q.CxtI)) {
return true;
} else if (Inv->getParent() == Q.CxtI->getParent()) {
// The context comes first, but they're both in the same block. Make sure
// there is nothing in between that might interrupt the control flow.
for (BasicBlock::const_iterator I =
std::next(BasicBlock::const_iterator(Q.CxtI)),
IE(Inv); I != IE; ++I)
if (!isSafeToSpeculativelyExecute(I, DL) &&
!isAssumeLikeIntrinsic(I))
return false;
return !isEphemeralValueOf(Inv, Q.CxtI);
}
return false;
}
// When we don't have a DT, we do a limited search...
if (Inv->getParent() == Q.CxtI->getParent()->getSinglePredecessor()) {
return true;
} else if (Inv->getParent() == Q.CxtI->getParent()) {
// Search forward from the assume until we reach the context (or the end
// of the block); the common case is that the assume will come first.
for (BasicBlock::iterator I = std::next(BasicBlock::iterator(Inv)),
IE = Inv->getParent()->end(); I != IE; ++I)
if (I == Q.CxtI)
return true;
// The context must come first...
for (BasicBlock::const_iterator I =
std::next(BasicBlock::const_iterator(Q.CxtI)),
IE(Inv); I != IE; ++I)
if (!isSafeToSpeculativelyExecute(I, DL) &&
!isAssumeLikeIntrinsic(I))
return false;
return !isEphemeralValueOf(Inv, Q.CxtI);
}
return false;
}
bool llvm::isValidAssumeForContext(const Instruction *I,
const Instruction *CxtI,
const DataLayout *DL,
const DominatorTree *DT) {
return ::isValidAssumeForContext(const_cast<Instruction*>(I),
Query(nullptr, CxtI, DT), DL);
}
template<typename LHS, typename RHS>
inline match_combine_or<CmpClass_match<LHS, RHS, ICmpInst, ICmpInst::Predicate>,
CmpClass_match<RHS, LHS, ICmpInst, ICmpInst::Predicate>>
m_c_ICmp(ICmpInst::Predicate &Pred, const LHS &L, const RHS &R) {
return m_CombineOr(m_ICmp(Pred, L, R), m_ICmp(Pred, R, L));
}
template<typename LHS, typename RHS>
inline match_combine_or<BinaryOp_match<LHS, RHS, Instruction::And>,
BinaryOp_match<RHS, LHS, Instruction::And>>
m_c_And(const LHS &L, const RHS &R) {
return m_CombineOr(m_And(L, R), m_And(R, L));
}
template<typename LHS, typename RHS>
inline match_combine_or<BinaryOp_match<LHS, RHS, Instruction::Or>,
BinaryOp_match<RHS, LHS, Instruction::Or>>
m_c_Or(const LHS &L, const RHS &R) {
return m_CombineOr(m_Or(L, R), m_Or(R, L));
}
template<typename LHS, typename RHS>
inline match_combine_or<BinaryOp_match<LHS, RHS, Instruction::Xor>,
BinaryOp_match<RHS, LHS, Instruction::Xor>>
m_c_Xor(const LHS &L, const RHS &R) {
return m_CombineOr(m_Xor(L, R), m_Xor(R, L));
}
static void computeKnownBitsFromAssume(Value *V, APInt &KnownZero,
APInt &KnownOne,
const DataLayout *DL,
unsigned Depth, const Query &Q) {
// Use of assumptions is context-sensitive. If we don't have a context, we
// cannot use them!
if (!Q.AC || !Q.CxtI)
return;
unsigned BitWidth = KnownZero.getBitWidth();
for (auto &AssumeVH : Q.AC->assumptions()) {
if (!AssumeVH)
continue;
CallInst *I = cast<CallInst>(AssumeVH);
assert(I->getParent()->getParent() == Q.CxtI->getParent()->getParent() &&
"Got assumption for the wrong function!");
if (Q.ExclInvs.count(I))
continue;
// Warning: This loop can end up being somewhat performance sensetive.
// We're running this loop for once for each value queried resulting in a
// runtime of ~O(#assumes * #values).
assert(isa<IntrinsicInst>(I) &&
dyn_cast<IntrinsicInst>(I)->getIntrinsicID() == Intrinsic::assume &&
"must be an assume intrinsic");
Value *Arg = I->getArgOperand(0);
if (Arg == V &&
isValidAssumeForContext(I, Q, DL)) {
assert(BitWidth == 1 && "assume operand is not i1?");
KnownZero.clearAllBits();
KnownOne.setAllBits();
return;
}
// The remaining tests are all recursive, so bail out if we hit the limit.
if (Depth == MaxDepth)
continue;
Value *A, *B;
auto m_V = m_CombineOr(m_Specific(V),
m_CombineOr(m_PtrToInt(m_Specific(V)),
m_BitCast(m_Specific(V))));
CmpInst::Predicate Pred;
ConstantInt *C;
// assume(v = a)
if (match(Arg, m_c_ICmp(Pred, m_V, m_Value(A))) &&
Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q, DL)) {
APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
KnownZero |= RHSKnownZero;
KnownOne |= RHSKnownOne;
// assume(v & b = a)
} else if (match(Arg, m_c_ICmp(Pred, m_c_And(m_V, m_Value(B)),
m_Value(A))) &&
Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q, DL)) {
APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
APInt MaskKnownZero(BitWidth, 0), MaskKnownOne(BitWidth, 0);
computeKnownBits(B, MaskKnownZero, MaskKnownOne, DL, Depth+1, Query(Q, I));
// For those bits in the mask that are known to be one, we can propagate
// known bits from the RHS to V.
KnownZero |= RHSKnownZero & MaskKnownOne;
KnownOne |= RHSKnownOne & MaskKnownOne;
// assume(~(v & b) = a)
} else if (match(Arg, m_c_ICmp(Pred, m_Not(m_c_And(m_V, m_Value(B))),
m_Value(A))) &&
Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q, DL)) {
APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
APInt MaskKnownZero(BitWidth, 0), MaskKnownOne(BitWidth, 0);
computeKnownBits(B, MaskKnownZero, MaskKnownOne, DL, Depth+1, Query(Q, I));
// For those bits in the mask that are known to be one, we can propagate
// inverted known bits from the RHS to V.
KnownZero |= RHSKnownOne & MaskKnownOne;
KnownOne |= RHSKnownZero & MaskKnownOne;
// assume(v | b = a)
} else if (match(Arg, m_c_ICmp(Pred, m_c_Or(m_V, m_Value(B)),
m_Value(A))) &&
Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q, DL)) {
APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
APInt BKnownZero(BitWidth, 0), BKnownOne(BitWidth, 0);
computeKnownBits(B, BKnownZero, BKnownOne, DL, Depth+1, Query(Q, I));
// For those bits in B that are known to be zero, we can propagate known
// bits from the RHS to V.
KnownZero |= RHSKnownZero & BKnownZero;
KnownOne |= RHSKnownOne & BKnownZero;
// assume(~(v | b) = a)
} else if (match(Arg, m_c_ICmp(Pred, m_Not(m_c_Or(m_V, m_Value(B))),
m_Value(A))) &&
Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q, DL)) {
APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
APInt BKnownZero(BitWidth, 0), BKnownOne(BitWidth, 0);
computeKnownBits(B, BKnownZero, BKnownOne, DL, Depth+1, Query(Q, I));
// For those bits in B that are known to be zero, we can propagate
// inverted known bits from the RHS to V.
KnownZero |= RHSKnownOne & BKnownZero;
KnownOne |= RHSKnownZero & BKnownZero;
// assume(v ^ b = a)
} else if (match(Arg, m_c_ICmp(Pred, m_c_Xor(m_V, m_Value(B)),
m_Value(A))) &&
Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q, DL)) {
APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
APInt BKnownZero(BitWidth, 0), BKnownOne(BitWidth, 0);
computeKnownBits(B, BKnownZero, BKnownOne, DL, Depth+1, Query(Q, I));
// For those bits in B that are known to be zero, we can propagate known
// bits from the RHS to V. For those bits in B that are known to be one,
// we can propagate inverted known bits from the RHS to V.
KnownZero |= RHSKnownZero & BKnownZero;
KnownOne |= RHSKnownOne & BKnownZero;
KnownZero |= RHSKnownOne & BKnownOne;
KnownOne |= RHSKnownZero & BKnownOne;
// assume(~(v ^ b) = a)
} else if (match(Arg, m_c_ICmp(Pred, m_Not(m_c_Xor(m_V, m_Value(B))),
m_Value(A))) &&
Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q, DL)) {
APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
APInt BKnownZero(BitWidth, 0), BKnownOne(BitWidth, 0);
computeKnownBits(B, BKnownZero, BKnownOne, DL, Depth+1, Query(Q, I));
// For those bits in B that are known to be zero, we can propagate
// inverted known bits from the RHS to V. For those bits in B that are
// known to be one, we can propagate known bits from the RHS to V.
KnownZero |= RHSKnownOne & BKnownZero;
KnownOne |= RHSKnownZero & BKnownZero;
KnownZero |= RHSKnownZero & BKnownOne;
KnownOne |= RHSKnownOne & BKnownOne;
// assume(v << c = a)
} else if (match(Arg, m_c_ICmp(Pred, m_Shl(m_V, m_ConstantInt(C)),
m_Value(A))) &&
Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q, DL)) {
APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
// For those bits in RHS that are known, we can propagate them to known
// bits in V shifted to the right by C.
KnownZero |= RHSKnownZero.lshr(C->getZExtValue());
KnownOne |= RHSKnownOne.lshr(C->getZExtValue());
// assume(~(v << c) = a)
} else if (match(Arg, m_c_ICmp(Pred, m_Not(m_Shl(m_V, m_ConstantInt(C))),
m_Value(A))) &&
Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q, DL)) {
APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
// For those bits in RHS that are known, we can propagate them inverted
// to known bits in V shifted to the right by C.
KnownZero |= RHSKnownOne.lshr(C->getZExtValue());
KnownOne |= RHSKnownZero.lshr(C->getZExtValue());
// assume(v >> c = a)
} else if (match(Arg,
m_c_ICmp(Pred, m_CombineOr(m_LShr(m_V, m_ConstantInt(C)),
m_AShr(m_V,
m_ConstantInt(C))),
m_Value(A))) &&
Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q, DL)) {
APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
// For those bits in RHS that are known, we can propagate them to known
// bits in V shifted to the right by C.
KnownZero |= RHSKnownZero << C->getZExtValue();
KnownOne |= RHSKnownOne << C->getZExtValue();
// assume(~(v >> c) = a)
} else if (match(Arg, m_c_ICmp(Pred, m_Not(m_CombineOr(
m_LShr(m_V, m_ConstantInt(C)),
m_AShr(m_V, m_ConstantInt(C)))),
m_Value(A))) &&
Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q, DL)) {
APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
// For those bits in RHS that are known, we can propagate them inverted
// to known bits in V shifted to the right by C.
KnownZero |= RHSKnownOne << C->getZExtValue();
KnownOne |= RHSKnownZero << C->getZExtValue();
// assume(v >=_s c) where c is non-negative
} else if (match(Arg, m_ICmp(Pred, m_V, m_Value(A))) &&
Pred == ICmpInst::ICMP_SGE &&
isValidAssumeForContext(I, Q, DL)) {
APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
if (RHSKnownZero.isNegative()) {
// We know that the sign bit is zero.
KnownZero |= APInt::getSignBit(BitWidth);
}
// assume(v >_s c) where c is at least -1.
} else if (match(Arg, m_ICmp(Pred, m_V, m_Value(A))) &&
Pred == ICmpInst::ICMP_SGT &&
isValidAssumeForContext(I, Q, DL)) {
APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
if (RHSKnownOne.isAllOnesValue() || RHSKnownZero.isNegative()) {
// We know that the sign bit is zero.
KnownZero |= APInt::getSignBit(BitWidth);
}
// assume(v <=_s c) where c is negative
} else if (match(Arg, m_ICmp(Pred, m_V, m_Value(A))) &&
Pred == ICmpInst::ICMP_SLE &&
isValidAssumeForContext(I, Q, DL)) {
APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
if (RHSKnownOne.isNegative()) {
// We know that the sign bit is one.
KnownOne |= APInt::getSignBit(BitWidth);
}
// assume(v <_s c) where c is non-positive
} else if (match(Arg, m_ICmp(Pred, m_V, m_Value(A))) &&
Pred == ICmpInst::ICMP_SLT &&
isValidAssumeForContext(I, Q, DL)) {
APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
if (RHSKnownZero.isAllOnesValue() || RHSKnownOne.isNegative()) {
// We know that the sign bit is one.
KnownOne |= APInt::getSignBit(BitWidth);
}
// assume(v <=_u c)
} else if (match(Arg, m_ICmp(Pred, m_V, m_Value(A))) &&
Pred == ICmpInst::ICMP_ULE &&
isValidAssumeForContext(I, Q, DL)) {
APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
// Whatever high bits in c are zero are known to be zero.
KnownZero |=
APInt::getHighBitsSet(BitWidth, RHSKnownZero.countLeadingOnes());
// assume(v <_u c)
} else if (match(Arg, m_ICmp(Pred, m_V, m_Value(A))) &&
Pred == ICmpInst::ICMP_ULT &&
isValidAssumeForContext(I, Q, DL)) {
APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
computeKnownBits(A, RHSKnownZero, RHSKnownOne, DL, Depth+1, Query(Q, I));
// 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)))
KnownZero |=
APInt::getHighBitsSet(BitWidth, RHSKnownZero.countLeadingOnes()+1);
else
KnownZero |=
APInt::getHighBitsSet(BitWidth, RHSKnownZero.countLeadingOnes());
}
}
}
/// Determine which bits of V are known to be either zero or one and return
/// them in the KnownZero/KnownOne bit sets.
///
/// 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.
///
/// This function is defined on values with integer type, values with pointer
/// type (but only if TD is non-null), and vectors of integers. In the case
/// where V is a vector, known zero, and known one values are the
/// same width as the vector element, and the bit is set only if it is true
/// for all of the elements in the vector.
void computeKnownBits(Value *V, APInt &KnownZero, APInt &KnownOne,
const DataLayout *TD, unsigned Depth,
const Query &Q) {
assert(V && "No Value?");
assert(Depth <= MaxDepth && "Limit Search Depth");
unsigned BitWidth = KnownZero.getBitWidth();
assert((V->getType()->isIntOrIntVectorTy() ||
V->getType()->getScalarType()->isPointerTy()) &&
"Not integer or pointer type!");
assert((!TD ||
TD->getTypeSizeInBits(V->getType()->getScalarType()) == BitWidth) &&
(!V->getType()->isIntOrIntVectorTy() ||
V->getType()->getScalarSizeInBits() == BitWidth) &&
KnownZero.getBitWidth() == BitWidth &&
KnownOne.getBitWidth() == BitWidth &&
"V, 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();
KnownZero = ~KnownOne;
return;
}
// Null and aggregate-zero are all-zeros.
if (isa<ConstantPointerNull>(V) ||
isa<ConstantAggregateZero>(V)) {
KnownOne.clearAllBits();
KnownZero = APInt::getAllOnesValue(BitWidth);
return;
}
// Handle a constant vector by taking the intersection of the known bits of
// each element. There is no real need to handle ConstantVector here, because
// we don't handle undef in any particularly useful way.
if (ConstantDataSequential *CDS = dyn_cast<ConstantDataSequential>(V)) {
// We know that CDS must be a vector of integers. Take the intersection of
// each element.
KnownZero.setAllBits(); KnownOne.setAllBits();
APInt Elt(KnownZero.getBitWidth(), 0);
for (unsigned i = 0, e = CDS->getNumElements(); i != e; ++i) {
Elt = CDS->getElementAsInteger(i);
KnownZero &= ~Elt;
KnownOne &= Elt;
}
return;
}
// The address of an aligned GlobalValue has trailing zeros.
if (auto *GO = dyn_cast<GlobalObject>(V)) {
unsigned Align = GO->getAlignment();
if (Align == 0 && TD) {
if (auto *GVar = dyn_cast<GlobalVariable>(GO)) {
Type *ObjectType = GVar->getType()->getElementType();
if (ObjectType->isSized()) {
// If the object is defined in the current Module, we'll be giving
// it the preferred alignment. Otherwise, we have to assume that it
// may only have the minimum ABI alignment.
if (!GVar->isDeclaration() && !GVar->isWeakForLinker())
Align = TD->getPreferredAlignment(GVar);
else
Align = TD->getABITypeAlignment(ObjectType);
}
}
}
if (Align > 0)
KnownZero = APInt::getLowBitsSet(BitWidth,
countTrailingZeros(Align));
else
KnownZero.clearAllBits();
KnownOne.clearAllBits();
return;
}
if (Argument *A = dyn_cast<Argument>(V)) {
unsigned Align = A->getType()->isPointerTy() ? A->getParamAlignment() : 0;
if (!Align && TD && A->hasStructRetAttr()) {
// An sret parameter has at least the ABI alignment of the return type.
Type *EltTy = cast<PointerType>(A->getType())->getElementType();
if (EltTy->isSized())
Align = TD->getABITypeAlignment(EltTy);
}
if (Align)
KnownZero = APInt::getLowBitsSet(BitWidth, countTrailingZeros(Align));
else
KnownZero.clearAllBits();
KnownOne.clearAllBits();
// Don't give up yet... there might be an assumption that provides more
// information...
computeKnownBitsFromAssume(V, KnownZero, KnownOne, TD, Depth, Q);
return;
}
// Start out not knowing anything.
KnownZero.clearAllBits(); KnownOne.clearAllBits();
// Limit search depth.
// All recursive calls that increase depth must come after this.
if (Depth == MaxDepth)
return;
// A weak GlobalAlias is totally unknown. A non-weak GlobalAlias has
// the bits of its aliasee.
if (GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) {
if (!GA->mayBeOverridden())
computeKnownBits(GA->getAliasee(), KnownZero, KnownOne, TD, Depth + 1, Q);
return;
}
// Check whether a nearby assume intrinsic can determine some known bits.
computeKnownBitsFromAssume(V, KnownZero, KnownOne, TD, Depth, Q);
Operator *I = dyn_cast<Operator>(V);
if (!I) return;
APInt KnownZero2(KnownZero), KnownOne2(KnownOne);
switch (I->getOpcode()) {
default: break;
case Instruction::Load:
if (MDNode *MD = cast<LoadInst>(I)->getMetadata(LLVMContext::MD_range))
computeKnownBitsFromRangeMetadata(*MD, KnownZero);
break;
case Instruction::And: {
// If either the LHS or the RHS are Zero, the result is zero.
computeKnownBits(I->getOperand(1), KnownZero, KnownOne, TD, Depth+1, Q);
computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, TD, Depth+1, Q);
// Output known-1 bits are only known if set in both the LHS & RHS.
KnownOne &= KnownOne2;
// Output known-0 are known to be clear if zero in either the LHS | RHS.
KnownZero |= KnownZero2;
break;
}
case Instruction::Or: {
computeKnownBits(I->getOperand(1), KnownZero, KnownOne, TD, Depth+1, Q);
computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, TD, Depth+1, Q);
// Output known-0 bits are only known if clear in both the LHS & RHS.
KnownZero &= KnownZero2;
// Output known-1 are known to be set if set in either the LHS | RHS.
KnownOne |= KnownOne2;
break;
}
case Instruction::Xor: {
computeKnownBits(I->getOperand(1), KnownZero, KnownOne, TD, Depth+1, Q);
computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, TD, Depth+1, Q);
// 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;
break;
}
case Instruction::Mul: {
bool NSW = cast<OverflowingBinaryOperator>(I)->hasNoSignedWrap();
computeKnownBitsMul(I->getOperand(0), I->getOperand(1), NSW,
KnownZero, KnownOne, KnownZero2, KnownOne2, TD,
Depth, Q);
break;
}
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.
computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, TD, Depth+1, Q);
unsigned LeadZ = KnownZero2.countLeadingOnes();
KnownOne2.clearAllBits();
KnownZero2.clearAllBits();
computeKnownBits(I->getOperand(1), KnownZero2, KnownOne2, TD, Depth+1, Q);
unsigned RHSUnknownLeadingOnes = KnownOne2.countLeadingZeros();
if (RHSUnknownLeadingOnes != BitWidth)
LeadZ = std::min(BitWidth,
LeadZ + BitWidth - RHSUnknownLeadingOnes - 1);
KnownZero = APInt::getHighBitsSet(BitWidth, LeadZ);
break;
}
case Instruction::Select:
computeKnownBits(I->getOperand(2), KnownZero, KnownOne, TD, Depth+1, Q);
computeKnownBits(I->getOperand(1), KnownZero2, KnownOne2, TD, Depth+1, Q);
// Only known if known in both the LHS and RHS.
KnownOne &= KnownOne2;
KnownZero &= KnownZero2;
break;
case Instruction::FPTrunc:
case Instruction::FPExt:
case Instruction::FPToUI:
case Instruction::FPToSI:
case Instruction::SIToFP:
case Instruction::UIToFP:
break; // Can't work with floating point.
case Instruction::PtrToInt:
case Instruction::IntToPtr:
case Instruction::AddrSpaceCast: // Pointers could be different sizes.
// We can't handle these if we don't know the pointer size.
if (!TD) break;
// FALL THROUGH and handle them the same as zext/trunc.
case Instruction::ZExt:
case Instruction::Trunc: {
Type *SrcTy = I->getOperand(0)->getType();
unsigned SrcBitWidth;
// Note that we handle pointer operands here because of inttoptr/ptrtoint
// which fall through here.
if(TD) {
SrcBitWidth = TD->getTypeSizeInBits(SrcTy->getScalarType());
} else {
SrcBitWidth = SrcTy->getScalarSizeInBits();
if (!SrcBitWidth) break;
}
assert(SrcBitWidth && "SrcBitWidth can't be zero");
KnownZero = KnownZero.zextOrTrunc(SrcBitWidth);
KnownOne = KnownOne.zextOrTrunc(SrcBitWidth);
computeKnownBits(I->getOperand(0), KnownZero, KnownOne, TD, Depth+1, Q);
KnownZero = KnownZero.zextOrTrunc(BitWidth);
KnownOne = KnownOne.zextOrTrunc(BitWidth);
// Any top bits are known to be zero.
if (BitWidth > SrcBitWidth)
KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth);
break;
}
case Instruction::BitCast: {
Type *SrcTy = I->getOperand(0)->getType();
if ((SrcTy->isIntegerTy() || SrcTy->isPointerTy()) &&
// TODO: For now, not handling conversions like:
// (bitcast i64 %x to <2 x i32>)
!I->getType()->isVectorTy()) {
computeKnownBits(I->getOperand(0), KnownZero, KnownOne, TD, Depth+1, Q);
break;
}
break;
}
case Instruction::SExt: {
// Compute the bits in the result that are not present in the input.
unsigned SrcBitWidth = I->getOperand(0)->getType()->getScalarSizeInBits();
KnownZero = KnownZero.trunc(SrcBitWidth);
KnownOne = KnownOne.trunc(SrcBitWidth);
computeKnownBits(I->getOperand(0), KnownZero, KnownOne, TD, Depth+1, Q);
KnownZero = KnownZero.zext(BitWidth);
KnownOne = 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);
break;
}
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);
computeKnownBits(I->getOperand(0), KnownZero, KnownOne, TD, Depth+1, Q);
KnownZero <<= ShiftAmt;
KnownOne <<= ShiftAmt;
KnownZero |= APInt::getLowBitsSet(BitWidth, ShiftAmt); // low bits known 0
}
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.
computeKnownBits(I->getOperand(0), KnownZero, KnownOne, TD, Depth+1, Q);
KnownZero = APIntOps::lshr(KnownZero, ShiftAmt);
KnownOne = APIntOps::lshr(KnownOne, ShiftAmt);
// high bits known zero.
KnownZero |= APInt::getHighBitsSet(BitWidth, ShiftAmt);
}
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-1);
// Signed shift right.
computeKnownBits(I->getOperand(0), KnownZero, KnownOne, TD, Depth+1, Q);
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;
}
break;
case Instruction::Sub: {
bool NSW = cast<OverflowingBinaryOperator>(I)->hasNoSignedWrap();
computeKnownBitsAddSub(false, I->getOperand(0), I->getOperand(1), NSW,
KnownZero, KnownOne, KnownZero2, KnownOne2, TD,
Depth, Q);
break;
}
case Instruction::Add: {
bool NSW = cast<OverflowingBinaryOperator>(I)->hasNoSignedWrap();
computeKnownBitsAddSub(true, I->getOperand(0), I->getOperand(1), NSW,
KnownZero, KnownOne, KnownZero2, KnownOne2, TD,
Depth, Q);
break;
}
case Instruction::SRem:
if (ConstantInt *Rem = dyn_cast<ConstantInt>(I->getOperand(1))) {
APInt RA = Rem->getValue().abs();
if (RA.isPowerOf2()) {
APInt LowBits = RA - 1;
computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, TD,
Depth+1, Q);
// The low bits of the first operand are unchanged by the srem.
KnownZero = KnownZero2 & LowBits;
KnownOne = KnownOne2 & LowBits;
// If the first operand is non-negative or has all low bits zero, then
// the upper bits are all zero.
if (KnownZero2[BitWidth-1] || ((KnownZero2 & LowBits) == LowBits))
KnownZero |= ~LowBits;
// If the first operand is negative and not all low bits are zero, then
// the upper bits are all one.
if (KnownOne2[BitWidth-1] && ((KnownOne2 & LowBits) != 0))
KnownOne |= ~LowBits;
assert((KnownZero & KnownOne) == 0 && "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 (KnownZero.isNonNegative()) {
APInt LHSKnownZero(BitWidth, 0), LHSKnownOne(BitWidth, 0);
computeKnownBits(I->getOperand(0), LHSKnownZero, LHSKnownOne, TD,
Depth+1, Q);
// If it's known zero, our sign bit is also zero.
if (LHSKnownZero.isNegative())
KnownZero.setBit(BitWidth - 1);
}
break;
case Instruction::URem: {
if (ConstantInt *Rem = dyn_cast<ConstantInt>(I->getOperand(1))) {
APInt RA = Rem->getValue();
if (RA.isPowerOf2()) {
APInt LowBits = (RA - 1);
computeKnownBits(I->getOperand(0), KnownZero, KnownOne, TD,
Depth+1, Q);
KnownZero |= ~LowBits;
KnownOne &= LowBits;
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.
computeKnownBits(I->getOperand(0), KnownZero, KnownOne, TD, Depth+1, Q);
computeKnownBits(I->getOperand(1), KnownZero2, KnownOne2, TD, Depth+1, Q);
unsigned Leaders = std::max(KnownZero.countLeadingOnes(),
KnownZero2.countLeadingOnes());
KnownOne.clearAllBits();
KnownZero = APInt::getHighBitsSet(BitWidth, Leaders);
break;
}
case Instruction::Alloca: {
AllocaInst *AI = cast<AllocaInst>(V);
unsigned Align = AI->getAlignment();
if (Align == 0 && TD)
Align = TD->getABITypeAlignment(AI->getType()->getElementType());
if (Align > 0)
KnownZero = APInt::getLowBitsSet(BitWidth, countTrailingZeros(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 LocalKnownZero(BitWidth, 0), LocalKnownOne(BitWidth, 0);
computeKnownBits(I->getOperand(0), LocalKnownZero, LocalKnownOne, TD,
Depth+1, Q);
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 (StructType *STy = dyn_cast<StructType>(*GTI)) {
// Handle struct member offset arithmetic.
if (!TD) {
TrailZ = 0;
break;
}
// Handle case when index is vector zeroinitializer
Constant *CIndex = cast<Constant>(Index);
if (CIndex->isZeroValue())
continue;
if (CIndex->getType()->isVectorTy())
Index = CIndex->getSplatValue();
unsigned Idx = cast<ConstantInt>(Index)->getZExtValue();
const StructLayout *SL = TD->getStructLayout(STy);
uint64_t Offset = SL->getElementOffset(Idx);
TrailZ = std::min<unsigned>(TrailZ,
countTrailingZeros(Offset));
} else {
// Handle array index arithmetic.
Type *IndexedTy = GTI.getIndexedType();
if (!IndexedTy->isSized()) {
TrailZ = 0;
break;
}
unsigned GEPOpiBits = Index->getType()->getScalarSizeInBits();
uint64_t TypeSize = TD ? TD->getTypeAllocSize(IndexedTy) : 1;
LocalKnownZero = LocalKnownOne = APInt(GEPOpiBits, 0);
computeKnownBits(Index, LocalKnownZero, LocalKnownOne, TD, Depth+1, Q);
TrailZ = std::min(TrailZ,
unsigned(countTrailingZeros(TypeSize) +
LocalKnownZero.countTrailingOnes()));
}
}
KnownZero = APInt::getLowBitsSet(BitWidth, TrailZ);
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);
Operator *LU = dyn_cast<Operator>(L);
if (!LU)
continue;
unsigned Opcode = LU->getOpcode();
// 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.
computeKnownBits(R, KnownZero2, KnownOne2, TD, Depth+1, Q);
// We need to take the minimum number of known bits
APInt KnownZero3(KnownZero), KnownOne3(KnownOne);
computeKnownBits(L, KnownZero3, KnownOne3, TD, Depth+1, Q);
KnownZero = APInt::getLowBitsSet(BitWidth,
std::min(KnownZero2.countTrailingOnes(),
KnownZero3.countTrailingOnes()));
break;
}
}
}
// Unreachable blocks may have zero-operand PHI nodes.
if (P->getNumIncomingValues() == 0)
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) {
// Skip if every incoming value references to ourself.
if (dyn_cast_or_null<UndefValue>(P->hasConstantValue()))
break;
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.
computeKnownBits(P->getIncomingValue(i), KnownZero2, KnownOne2, TD,
MaxDepth-1, Q);
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:
case Instruction::Invoke:
if (MDNode *MD = cast<Instruction>(I)->getMetadata(LLVMContext::MD_range))
computeKnownBitsFromRangeMetadata(*MD, KnownZero);
// If a range metadata is attached to this IntrinsicInst, intersect the
// explicit range specified by the metadata and the implicit range of
// the intrinsic.
if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
switch (II->getIntrinsicID()) {
default: break;
case Intrinsic::ctlz:
case Intrinsic::cttz: {
unsigned LowBits = Log2_32(BitWidth)+1;
// 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;
KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - LowBits);
break;
}
case Intrinsic::ctpop: {
unsigned LowBits = Log2_32(BitWidth)+1;
KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - LowBits);
break;
}
case Intrinsic::x86_sse42_crc32_64_64:
KnownZero |= APInt::getHighBitsSet(64, 32);
break;
}
}
break;
case Instruction::ExtractValue:
if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I->getOperand(0))) {
ExtractValueInst *EVI = cast<ExtractValueInst>(I);
if (EVI->getNumIndices() != 1) break;
if (EVI->getIndices()[0] == 0) {
switch (II->getIntrinsicID()) {
default: break;
case Intrinsic::uadd_with_overflow:
case Intrinsic::sadd_with_overflow:
computeKnownBitsAddSub(true, II->getArgOperand(0),
II->getArgOperand(1), false, KnownZero,
KnownOne, KnownZero2, KnownOne2, TD, Depth, Q);
break;
case Intrinsic::usub_with_overflow:
case Intrinsic::ssub_with_overflow:
computeKnownBitsAddSub(false, II->getArgOperand(0),
II->getArgOperand(1), false, KnownZero,
KnownOne, KnownZero2, KnownOne2, TD, Depth, Q);
break;
case Intrinsic::umul_with_overflow:
case Intrinsic::smul_with_overflow:
computeKnownBitsMul(II->getArgOperand(0), II->getArgOperand(1),
false, KnownZero, KnownOne,
KnownZero2, KnownOne2, TD, Depth, Q);
break;
}
}
}
}
assert((KnownZero & KnownOne) == 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(Value *V, bool &KnownZero, bool &KnownOne,
const DataLayout *TD, unsigned Depth,
const Query &Q) {
unsigned BitWidth = getBitWidth(V->getType(), TD);
if (!BitWidth) {
KnownZero = false;
KnownOne = false;
return;
}
APInt ZeroBits(BitWidth, 0);
APInt OneBits(BitWidth, 0);
computeKnownBits(V, ZeroBits, OneBits, TD, Depth, Q);
KnownOne = OneBits[BitWidth - 1];
KnownZero = ZeroBits[BitWidth - 1];
}
/// 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
/// types and vectors of integers.
bool isKnownToBeAPowerOfTwo(Value *V, bool OrZero, unsigned Depth,
const Query &Q) {
if (Constant *C = dyn_cast<Constant>(V)) {
if (C->isNullValue())
return OrZero;
if (ConstantInt *CI = dyn_cast<ConstantInt>(C))
return CI->getValue().isPowerOf2();
// TODO: Handle vector constants.
}
// 1 << X is clearly a power of two if the one is not shifted off the end. If
// it is shifted off the end then the result is undefined.
if (match(V, m_Shl(m_One(), m_Value())))
return true;
// (signbit) >>l X is clearly a power of two if the one is not shifted off the
// bottom. If it is shifted off the bottom then the result is undefined.
if (match(V, m_LShr(m_SignBit(), m_Value())))
return true;
// The remaining tests are all recursive, so bail out if we hit the limit.
if (Depth++ == MaxDepth)
return false;
Value *X = nullptr, *Y = nullptr;
// A shift of a power of two is a power of two or zero.
if (OrZero && (match(V, m_Shl(m_Value(X), m_Value())) ||
match(V, m_Shr(m_Value(X), m_Value()))))
return isKnownToBeAPowerOfTwo(X, /*OrZero*/true, Depth, Q);
if (ZExtInst *ZI = dyn_cast<ZExtInst>(V))
return isKnownToBeAPowerOfTwo(ZI->getOperand(0), OrZero, Depth, Q);
if (SelectInst *SI = dyn_cast<SelectInst>(V))
return
isKnownToBeAPowerOfTwo(SI->getTrueValue(), OrZero, Depth, Q) &&
isKnownToBeAPowerOfTwo(SI->getFalseValue(), OrZero, Depth, Q);
if (OrZero && match(V, m_And(m_Value(X), m_Value(Y)))) {
// A power of two and'd with anything is a power of two or zero.
if (isKnownToBeAPowerOfTwo(X, /*OrZero*/true, Depth, Q) ||
isKnownToBeAPowerOfTwo(Y, /*OrZero*/true, Depth, Q))
return true;
// X & (-X) is always a power of two or zero.
if (match(X, m_Neg(m_Specific(Y))) || match(Y, m_Neg(m_Specific(X))))
return true;
return false;
}
// Adding a power-of-two or zero to the same power-of-two or zero yields
// either the original power-of-two, a larger power-of-two or zero.
if (match(V, m_Add(m_Value(X), m_Value(Y)))) {
OverflowingBinaryOperator *VOBO = cast<OverflowingBinaryOperator>(V);
if (OrZero || VOBO->hasNoUnsignedWrap() || VOBO->hasNoSignedWrap()) {
if (match(X, m_And(m_Specific(Y), m_Value())) ||
match(X, m_And(m_Value(), m_Specific(Y))))
if (isKnownToBeAPowerOfTwo(Y, OrZero, Depth, Q))
return true;
if (match(Y, m_And(m_Specific(X), m_Value())) ||
match(Y, m_And(m_Value(), m_Specific(X))))
if (isKnownToBeAPowerOfTwo(X, OrZero, Depth, Q))
return true;
unsigned BitWidth = V->getType()->getScalarSizeInBits();
APInt LHSZeroBits(BitWidth, 0), LHSOneBits(BitWidth, 0);
computeKnownBits(X, LHSZeroBits, LHSOneBits, nullptr, Depth, Q);
APInt RHSZeroBits(BitWidth, 0), RHSOneBits(BitWidth, 0);
computeKnownBits(Y, RHSZeroBits, RHSOneBits, nullptr, Depth, Q);
// If i8 V is a power of two or zero:
// ZeroBits: 1 1 1 0 1 1 1 1
// ~ZeroBits: 0 0 0 1 0 0 0 0
if ((~(LHSZeroBits & RHSZeroBits)).isPowerOf2())
// If OrZero isn't set, we cannot give back a zero result.
// Make sure either the LHS or RHS has a bit set.
if (OrZero || RHSOneBits.getBoolValue() || LHSOneBits.getBoolValue())
return true;
}
}
// An exact divide or right shift can only shift off zero bits, so the result
// is a power of two only if the first operand is a power of two and not
// copying a sign bit (sdiv int_min, 2).
if (match(V, m_Exact(m_LShr(m_Value(), m_Value()))) ||
match(V, m_Exact(m_UDiv(m_Value(), m_Value())))) {
return isKnownToBeAPowerOfTwo(cast<Operator>(V)->getOperand(0), OrZero,
Depth, Q);
}
return false;
}
/// \brief Test whether a GEP's result is known to be non-null.
///
/// Uses properties inherent in a GEP to try to determine whether it is known
/// to be non-null.
///
/// Currently this routine does not support vector GEPs.
static bool isGEPKnownNonNull(GEPOperator *GEP, const DataLayout *DL,
unsigned Depth, const Query &Q) {
if (!GEP->isInBounds() || GEP->getPointerAddressSpace() != 0)
return false;
// FIXME: Support vector-GEPs.
assert(GEP->getType()->isPointerTy() && "We only support plain pointer GEP");
// If the base pointer is non-null, we cannot walk to a null address with an
// inbounds GEP in address space zero.
if (isKnownNonZero(GEP->getPointerOperand(), DL, Depth, Q))
return true;
// Past this, if we don't have DataLayout, we can't do much.
if (!DL)
return false;
// Walk the GEP operands and see if any operand introduces a non-zero offset.
// If so, then the GEP cannot produce a null pointer, as doing so would
// inherently violate the inbounds contract within address space zero.
for (gep_type_iterator GTI = gep_type_begin(GEP), GTE = gep_type_end(GEP);
GTI != GTE; ++GTI) {
// Struct types are easy -- they must always be indexed by a constant.
if (StructType *STy = dyn_cast<StructType>(*GTI)) {
ConstantInt *OpC = cast<ConstantInt>(GTI.getOperand());
unsigned ElementIdx = OpC->getZExtValue();
const StructLayout *SL = DL->getStructLayout(STy);
uint64_t ElementOffset = SL->getElementOffset(ElementIdx);
if (ElementOffset > 0)
return true;
continue;
}
// If we have a zero-sized type, the index doesn't matter. Keep looping.
if (DL->getTypeAllocSize(GTI.getIndexedType()) == 0)
continue;
// Fast path the constant operand case both for efficiency and so we don't
// increment Depth when just zipping down an all-constant GEP.
if (ConstantInt *OpC = dyn_cast<ConstantInt>(GTI.getOperand())) {
if (!OpC->isZero())
return true;
continue;
}
// We post-increment Depth here because while isKnownNonZero increments it
// as well, when we pop back up that increment won't persist. We don't want
// to recurse 10k times just because we have 10k GEP operands. We don't
// bail completely out because we want to handle constant GEPs regardless
// of depth.
if (Depth++ >= MaxDepth)
continue;
if (isKnownNonZero(GTI.getOperand(), DL, Depth, Q))
return true;
}
return false;
}
/// Does the 'Range' metadata (which must be a valid MD_range operand list)
/// ensure that the value it's attached to is never Value? 'RangeType' is
/// is the type of the value described by the range.
static bool rangeMetadataExcludesValue(MDNode* Ranges,
const APInt& Value) {
const unsigned NumRanges = Ranges->getNumOperands() / 2;
assert(NumRanges >= 1);
for (unsigned i = 0; i < NumRanges; ++i) {
ConstantInt *Lower =
mdconst::extract<ConstantInt>(Ranges->getOperand(2 * i + 0));
ConstantInt *Upper =
mdconst::extract<ConstantInt>(Ranges->getOperand(2 * i + 1));
ConstantRange Range(Lower->getValue(), Upper->getValue());
if (Range.contains(Value))
return false;
}
return true;
}
/// Return true if the given value is known to be non-zero when defined.
/// For vectors return true if every element is known to be non-zero when
/// defined. Supports values with integer or pointer type and vectors of
/// integers.
bool isKnownNonZero(Value *V, const DataLayout *TD, unsigned Depth,
const Query &Q) {
if (Constant *C = dyn_cast<Constant>(V)) {
if (C->isNullValue())
return false;
if (isa<ConstantInt>(C))
// Must be non-zero due to null test above.
return true;
// TODO: Handle vectors
return false;
}
if (Instruction* I = dyn_cast<Instruction>(V)) {
if (MDNode *Ranges = I->getMetadata(LLVMContext::MD_range)) {
// If the possible ranges don't contain zero, then the value is
// definitely non-zero.
if (IntegerType* Ty = dyn_cast<IntegerType>(V->getType())) {
const APInt ZeroValue(Ty->getBitWidth(), 0);
if (rangeMetadataExcludesValue(Ranges, ZeroValue))
return true;
}
}
}
// The remaining tests are all recursive, so bail out if we hit the limit.
if (Depth++ >= MaxDepth)
return false;
// Check for pointer simplifications.
if (V->getType()->isPointerTy()) {
if (isKnownNonNull(V))
return true;
if (GEPOperator *GEP = dyn_cast<GEPOperator>(V))
if (isGEPKnownNonNull(GEP, TD, Depth, Q))
return true;
}
unsigned BitWidth = getBitWidth(V->getType()->getScalarType(), TD);
// X | Y != 0 if X != 0 or Y != 0.
Value *X = nullptr, *Y = nullptr;
if (match(V, m_Or(m_Value(X), m_Value(Y))))
return isKnownNonZero(X, TD, Depth, Q) ||
isKnownNonZero(Y, TD, Depth, Q);
// ext X != 0 if X != 0.
if (isa<SExtInst>(V) || isa<ZExtInst>(V))
return isKnownNonZero(cast<Instruction>(V)->getOperand(0), TD, Depth, Q);
// shl X, Y != 0 if X is odd. Note that the value of the shift is undefined
// if the lowest bit is shifted off the end.
if (BitWidth && match(V, m_Shl(m_Value(X), m_Value(Y)))) {
// shl nuw can't remove any non-zero bits.
OverflowingBinaryOperator *BO = cast<OverflowingBinaryOperator>(V);
if (BO->hasNoUnsignedWrap())
return isKnownNonZero(X, TD, Depth, Q);
APInt KnownZero(BitWidth, 0);
APInt KnownOne(BitWidth, 0);
computeKnownBits(X, KnownZero, KnownOne, TD, Depth, Q);
if (KnownOne[0])
return true;
}
// shr X, Y != 0 if X is negative. Note that the value of the shift is not
// defined if the sign bit is shifted off the end.
else if (match(V, m_Shr(m_Value(X), m_Value(Y)))) {
// shr exact can only shift out zero bits.
PossiblyExactOperator *BO = cast<PossiblyExactOperator>(V);
if (BO->isExact())
return isKnownNonZero(X, TD, Depth, Q);
bool XKnownNonNegative, XKnownNegative;
ComputeSignBit(X, XKnownNonNegative, XKnownNegative, TD, Depth, Q);
if (XKnownNegative)
return true;
}
// div exact can only produce a zero if the dividend is zero.
else if (match(V, m_Exact(m_IDiv(m_Value(X), m_Value())))) {
return isKnownNonZero(X, TD, Depth, 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, TD, Depth, Q);
ComputeSignBit(Y, YKnownNonNegative, YKnownNegative, TD, 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 (isKnownNonZero(X, TD, Depth, Q) ||
isKnownNonZero(Y, TD, 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 (BitWidth && XKnownNegative && YKnownNegative) {
APInt KnownZero(BitWidth, 0);
APInt KnownOne(BitWidth, 0);
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, KnownZero, KnownOne, TD, Depth, Q);
if ((KnownOne & Mask) != 0)
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, KnownZero, KnownOne, TD, Depth, Q);
if ((KnownOne & Mask) != 0)
return true;
}
// The sum of a non-negative number and a power of two is not zero.
if (XKnownNonNegative &&
isKnownToBeAPowerOfTwo(Y, /*OrZero*/false, Depth, Q))
return true;
if (YKnownNonNegative &&
isKnownToBeAPowerOfTwo(X, /*OrZero*/false, Depth, Q))
return true;
}
// X * Y.
else if (match(V, m_Mul(m_Value(X), m_Value(Y)))) {
OverflowingBinaryOperator *BO = cast<OverflowingBinaryOperator>(V);
// If X and Y are non-zero then so is X * Y as long as the multiplication
// does not overflow.
if ((BO->hasNoSignedWrap() || BO->hasNoUnsignedWrap()) &&
isKnownNonZero(X, TD, Depth, Q) &&
isKnownNonZero(Y, TD, Depth, Q))
return true;
}
// (C ? X : Y) != 0 if X != 0 and Y != 0.
else if (SelectInst *SI = dyn_cast<SelectInst>(V)) {
if (isKnownNonZero(SI->getTrueValue(), TD, Depth, Q) &&
isKnownNonZero(SI->getFalseValue(), TD, Depth, Q))
return true;
}
if (!BitWidth) return false;
APInt KnownZero(BitWidth, 0);
APInt KnownOne(BitWidth, 0);
computeKnownBits(V, KnownZero, KnownOne, TD, Depth, Q);
return KnownOne != 0;
}
/// Return true if 'V & Mask' is known to be zero. We use this predicate to
/// simplify operations downstream. Mask is known to be zero for bits that V
/// cannot have.
///
/// This function is defined on values with integer type, values with pointer
/// type (but only if TD is non-null), and vectors of integers. In the case
/// where V is a vector, the mask, known zero, and known one values are the
/// same width as the vector element, and the bit is set only if it is true
/// for all of the elements in the vector.
bool MaskedValueIsZero(Value *V, const APInt &Mask,
const DataLayout *TD, unsigned Depth,
const Query &Q) {
APInt KnownZero(Mask.getBitWidth(), 0), KnownOne(Mask.getBitWidth(), 0);
computeKnownBits(V, KnownZero, KnownOne, TD, Depth, Q);
return (KnownZero & Mask) == Mask;
}
/// Return the number of times the sign bit of the register is replicated into
/// the other bits. We know that at least 1 bit is always equal to the sign bit
/// (itself), but other cases can give us information. For example, immediately
/// after an "ashr X, 2", we know that the top 3 bits are all equal to each
/// other, so we return 3.
///
/// 'Op' must have a scalar integer type.
///
unsigned ComputeNumSignBits(Value *V, const DataLayout *TD,
unsigned Depth, const Query &Q) {
assert((TD || V->getType()->isIntOrIntVectorTy()) &&
"ComputeNumSignBits requires a DataLayout object to operate "
"on non-integer values!");
Type *Ty = V->getType();
unsigned TyBits = TD ? TD->getTypeSizeInBits(V->getType()->getScalarType()) :
Ty->getScalarSizeInBits();
unsigned Tmp, Tmp2;
unsigned FirstAnswer = 1;
// Note that ConstantInt is handled by the general computeKnownBits case
// below.
if (Depth == 6)
return 1; // Limit search depth.
Operator *U = dyn_cast<Operator>(V);
switch (Operator::getOpcode(V)) {
default: break;
case Instruction::SExt:
Tmp = TyBits - U->getOperand(0)->getType()->getScalarSizeInBits();
return ComputeNumSignBits(U->getOperand(0), TD, Depth+1, Q) + Tmp;
case Instruction::AShr: {
Tmp = ComputeNumSignBits(U->getOperand(0), TD, Depth+1, Q);
// ashr X, C -> adds C sign bits. Vectors too.
const APInt *ShAmt;
if (match(U->getOperand(1), m_APInt(ShAmt))) {
Tmp += ShAmt->getZExtValue();
if (Tmp > TyBits) Tmp = TyBits;
}
return Tmp;
}
case Instruction::Shl: {
const APInt *ShAmt;
if (match(U->getOperand(1), m_APInt(ShAmt))) {
// shl destroys sign bits.
Tmp = ComputeNumSignBits(U->getOperand(0), TD, Depth+1, Q);
Tmp2 = ShAmt->getZExtValue();
if (Tmp2 >= TyBits || // Bad shift.
Tmp2 >= Tmp) break; // Shifted all sign bits out.
return Tmp - Tmp2;
}
break;
}
case Instruction::And:
case Instruction::Or:
case Instruction::Xor: // NOT is handled here.
// Logical binary ops preserve the number of sign bits at the worst.
Tmp = ComputeNumSignBits(U->getOperand(0), TD, Depth+1, Q);
if (Tmp != 1) {
Tmp2 = ComputeNumSignBits(U->getOperand(1), TD, Depth+1, Q);
FirstAnswer = std::min(Tmp, Tmp2);
// We computed what we know about the sign bits as our first
// answer. Now proceed to the generic code that uses
// computeKnownBits, and pick whichever answer is better.
}
break;
case Instruction::Select:
Tmp = ComputeNumSignBits(U->getOperand(1), TD, Depth+1, Q);
if (Tmp == 1) return 1; // Early out.
Tmp2 = ComputeNumSignBits(U->getOperand(2), TD, Depth+1, Q);
return std::min(Tmp, Tmp2);
case Instruction::Add:
// Add can have at most one carry bit. Thus we know that the output
// is, at worst, one more bit than the inputs.
Tmp = ComputeNumSignBits(U->getOperand(0), TD, Depth+1, Q);
if (Tmp == 1) return 1; // Early out.
// Special case decrementing a value (ADD X, -1):
if (const auto *CRHS = dyn_cast<Constant>(U->getOperand(1)))
if (CRHS->isAllOnesValue()) {
APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0);
computeKnownBits(U->getOperand(0), KnownZero, KnownOne, TD, Depth+1, Q);
// If the input is known to be 0 or 1, the output is 0/-1, which is all
// sign bits set.
if ((KnownZero | APInt(TyBits, 1)).isAllOnesValue())
return TyBits;
// If we are subtracting one from a positive number, there is no carry
// out of the result.
if (KnownZero.isNegative())
return Tmp;
}
Tmp2 = ComputeNumSignBits(U->getOperand(1), TD, Depth+1, Q);
if (Tmp2 == 1) return 1;
return std::min(Tmp, Tmp2)-1;
case Instruction::Sub:
Tmp2 = ComputeNumSignBits(U->getOperand(1), TD, Depth+1, Q);
if (Tmp2 == 1) return 1;
// Handle NEG.
if (const auto *CLHS = dyn_cast<Constant>(U->getOperand(0)))
if (CLHS->isNullValue()) {
APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0);
computeKnownBits(U->getOperand(1), KnownZero, KnownOne, TD, Depth+1, Q);
// If the input is known to be 0 or 1, the output is 0/-1, which is all
// sign bits set.
if ((KnownZero | APInt(TyBits, 1)).isAllOnesValue())
return TyBits;
// If the input is known to be positive (the sign bit is known clear),
// the output of the NEG has the same number of sign bits as the input.
if (KnownZero.isNegative())
return Tmp2;
// Otherwise, we treat this like a SUB.
}
// Sub can have at most one carry bit. Thus we know that the output
// is, at worst, one more bit than the inputs.
Tmp = ComputeNumSignBits(U->getOperand(0), TD, Depth+1, Q);
if (Tmp == 1) return 1; // Early out.
return std::min(Tmp, Tmp2)-1;
case Instruction::PHI: {
PHINode *PN = cast<PHINode>(U);
unsigned NumIncomingValues = PN->getNumIncomingValues();
// Don't analyze large in-degree PHIs.
if (NumIncomingValues > 4) break;
// Unreachable blocks may have zero-operand PHI nodes.
if (NumIncomingValues == 0) break;
// Take the minimum of all incoming values. This can't infinitely loop
// because of our depth threshold.
Tmp = ComputeNumSignBits(PN->getIncomingValue(0), TD, Depth+1, Q);
for (unsigned i = 1, e = NumIncomingValues; i != e; ++i) {
if (Tmp == 1) return Tmp;
Tmp = std::min(Tmp,
ComputeNumSignBits(PN->getIncomingValue(i), TD,
Depth+1, Q));
}
return Tmp;
}
case Instruction::Trunc:
// FIXME: it's tricky to do anything useful for this, but it is an important
// case for targets like X86.
break;
}
// Finally, if we can prove that the top bits of the result are 0's or 1's,
// use this information.
APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0);
APInt Mask;
computeKnownBits(V, KnownZero, KnownOne, TD, Depth, Q);
if (KnownZero.isNegative()) { // sign bit is 0
Mask = KnownZero;
} else if (KnownOne.isNegative()) { // sign bit is 1;
Mask = KnownOne;
} else {
// Nothing known.
return FirstAnswer;
}
// Okay, we know that the sign bit in Mask is set. Use CLZ to determine
// the number of identical bits in the top of the input value.
Mask = ~Mask;
Mask <<= Mask.getBitWidth()-TyBits;
// Return # leading zeros. We use 'min' here in case Val was zero before
// shifting. We don't want to return '64' as for an i32 "0".
return std::max(FirstAnswer, std::min(TyBits, Mask.countLeadingZeros()));
}
/// This function computes the integer multiple of Base that equals V.
/// If successful, it returns true and returns the multiple in
/// Multiple. If unsuccessful, it returns false. It looks
/// through SExt instructions only if LookThroughSExt is true.
bool llvm::ComputeMultiple(Value *V, unsigned Base, Value *&Multiple,
bool LookThroughSExt, unsigned Depth) {
const unsigned MaxDepth = 6;
assert(V && "No Value?");
assert(Depth <= MaxDepth && "Limit Search Depth");
assert(V->getType()->isIntegerTy() && "Not integer or pointer type!");
Type *T = V->getType();
ConstantInt *CI = dyn_cast<ConstantInt>(V);
if (Base == 0)
return false;
if (Base == 1) {
Multiple = V;
return true;
}
ConstantExpr *CO = dyn_cast<ConstantExpr>(V);
Constant *BaseVal = ConstantInt::get(T, Base);
if (CO && CO == BaseVal) {
// Multiple is 1.
Multiple = ConstantInt::get(T, 1);
return true;
}
if (CI && CI->getZExtValue() % Base == 0) {
Multiple = ConstantInt::get(T, CI->getZExtValue() / Base);
return true;
}
if (Depth == MaxDepth) return false; // Limit search depth.
Operator *I = dyn_cast<Operator>(V);
if (!I) return false;
switch (I->getOpcode()) {
default: break;
case Instruction::SExt:
if (!LookThroughSExt) return false;
// otherwise fall through to ZExt
case Instruction::ZExt:
return ComputeMultiple(I->getOperand(0), Base, Multiple,
LookThroughSExt, Depth+1);
case Instruction::Shl:
case Instruction::Mul: {
Value *Op0 = I->getOperand(0);
Value *Op1 = I->getOperand(1);
if (I->getOpcode() == Instruction::Shl) {
ConstantInt *Op1CI = dyn_cast<ConstantInt>(Op1);
if (!Op1CI) return false;
// Turn Op0 << Op1 into Op0 * 2^Op1
APInt Op1Int = Op1CI->getValue();
uint64_t BitToSet = Op1Int.getLimitedValue(Op1Int.getBitWidth() - 1);
APInt API(Op1Int.getBitWidth(), 0);
API.setBit(BitToSet);
Op1 = ConstantInt::get(V->getContext(), API);
}
Value *Mul0 = nullptr;
if (ComputeMultiple(Op0, Base, Mul0, LookThroughSExt, Depth+1)) {
if (Constant *Op1C = dyn_cast<Constant>(Op1))
if (Constant *MulC = dyn_cast<Constant>(Mul0)) {
if (Op1C->getType()->getPrimitiveSizeInBits() <
MulC->getType()->getPrimitiveSizeInBits())
Op1C = ConstantExpr::getZExt(Op1C, MulC->getType());
if (Op1C->getType()->getPrimitiveSizeInBits() >
MulC->getType()->getPrimitiveSizeInBits())
MulC = ConstantExpr::getZExt(MulC, Op1C->getType());
// V == Base * (Mul0 * Op1), so return (Mul0 * Op1)
Multiple = ConstantExpr::getMul(MulC, Op1C);
return true;
}
if (ConstantInt *Mul0CI = dyn_cast<ConstantInt>(Mul0))
if (Mul0CI->getValue() == 1) {
// V == Base * Op1, so return Op1
Multiple = Op1;
return true;
}
}
Value *Mul1 = nullptr;
if (ComputeMultiple(Op1, Base, Mul1, LookThroughSExt, Depth+1)) {
if (Constant *Op0C = dyn_cast<Constant>(Op0))
if (Constant *MulC = dyn_cast<Constant>(Mul1)) {
if (Op0C->getType()->getPrimitiveSizeInBits() <
MulC->getType()->getPrimitiveSizeInBits())
Op0C = ConstantExpr::getZExt(Op0C, MulC->getType());
if (Op0C->getType()->getPrimitiveSizeInBits() >
MulC->getType()->getPrimitiveSizeInBits())
MulC = ConstantExpr::getZExt(MulC, Op0C->getType());
// V == Base * (Mul1 * Op0), so return (Mul1 * Op0)
Multiple = ConstantExpr::getMul(MulC, Op0C);
return true;
}
if (ConstantInt *Mul1CI = dyn_cast<ConstantInt>(Mul1))
if (Mul1CI->getValue() == 1) {
// V == Base * Op0, so return Op0
Multiple = Op0;
return true;
}
}
}
}
// We could not determine if V is a multiple of Base.
return false;
}
/// Return true if we can prove that the specified FP value is never equal to
/// -0.0.
///
/// NOTE: this function will need to be revisited when we support non-default
/// rounding modes!
///
bool llvm::CannotBeNegativeZero(const Value *V, unsigned Depth) {
if (const ConstantFP *CFP = dyn_cast<ConstantFP>(V))
return !CFP->getValueAPF().isNegZero();
// FIXME: Magic number! At the least, this should be given a name because it's
// used similarly in CannotBeOrderedLessThanZero(). A better fix may be to
// expose it as a parameter, so it can be used for testing / experimenting.
if (Depth == 6)
return false; // Limit search depth.
const Operator *I = dyn_cast<Operator>(V);
if (!I) return false;
// Check if the nsz fast-math flag is set
if (const FPMathOperator *FPO = dyn_cast<FPMathOperator>(I))
if (FPO->hasNoSignedZeros())
return true;
// (add x, 0.0) is guaranteed to return +0.0, not -0.0.
if (I->getOpcode() == Instruction::FAdd)
if (ConstantFP *CFP = dyn_cast<ConstantFP>(I->getOperand(1)))
if (CFP->isNullValue())
return true;
// sitofp and uitofp turn into +0.0 for zero.
if (isa<SIToFPInst>(I) || isa<UIToFPInst>(I))
return true;
if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(I))
// sqrt(-0.0) = -0.0, no other negative results are possible.
if (II->getIntrinsicID() == Intrinsic::sqrt)
return CannotBeNegativeZero(II->getArgOperand(0), Depth+1);
if (const CallInst *CI = dyn_cast<CallInst>(I))
if (const Function *F = CI->getCalledFunction()) {
if (F->isDeclaration()) {
// abs(x) != -0.0
if (F->getName() == "abs") return true;
// fabs[lf](x) != -0.0
if (F->getName() == "fabs") return true;
if (F->getName() == "fabsf") return true;
if (F->getName() == "fabsl") return true;
if (F->getName() == "sqrt" || F->getName() == "sqrtf" ||
F->getName() == "sqrtl")
return CannotBeNegativeZero(CI->getArgOperand(0), Depth+1);
}
}
return false;
}
bool llvm::CannotBeOrderedLessThanZero(const Value *V, unsigned Depth) {
if (const ConstantFP *CFP = dyn_cast<ConstantFP>(V))
return !CFP->getValueAPF().isNegative() || CFP->getValueAPF().isZero();
// FIXME: Magic number! At the least, this should be given a name because it's
// used similarly in CannotBeNegativeZero(). A better fix may be to
// expose it as a parameter, so it can be used for testing / experimenting.
if (Depth == 6)
return false; // Limit search depth.
const Operator *I = dyn_cast<Operator>(V);
if (!I) return false;
switch (I->getOpcode()) {
default: break;
case Instruction::FMul:
// x*x is always non-negative or a NaN.
if (I->getOperand(0) == I->getOperand(1))
return true;
// Fall through
case Instruction::FAdd:
case Instruction::FDiv:
case Instruction::FRem:
return CannotBeOrderedLessThanZero(I->getOperand(0), Depth+1) &&
CannotBeOrderedLessThanZero(I->getOperand(1), Depth+1);
case Instruction::FPExt:
case Instruction::FPTrunc:
// Widening/narrowing never change sign.
return CannotBeOrderedLessThanZero(I->getOperand(0), Depth+1);
case Instruction::Call:
if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(I))
switch (II->getIntrinsicID()) {
default: break;
case Intrinsic::exp:
case Intrinsic::exp2:
case Intrinsic::fabs:
case Intrinsic::sqrt:
return true;
case Intrinsic::powi:
if (ConstantInt *CI = dyn_cast<ConstantInt>(I->getOperand(1))) {
// powi(x,n) is non-negative if n is even.
if (CI->getBitWidth() <= 64 && CI->getSExtValue() % 2u == 0)
return true;
}
return CannotBeOrderedLessThanZero(I->getOperand(0), Depth+1);
case Intrinsic::fma:
case Intrinsic::fmuladd:
// x*x+y is non-negative if y is non-negative.
return I->getOperand(0) == I->getOperand(1) &&
CannotBeOrderedLessThanZero(I->getOperand(2), Depth+1);
}
break;
}
return false;
}
/// 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.
Value *llvm::isBytewiseValue(Value *V) {
// All byte-wide stores are splatable, even of arbitrary variables.
if (V->getType()->isIntegerTy(8)) return V;
// Handle 'null' ConstantArrayZero etc.
if (Constant *C = dyn_cast<Constant>(V))
if (C->isNullValue())
return Constant::getNullValue(Type::getInt8Ty(V->getContext()));
// 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(V->getContext()));
if (CFP->getType()->isDoubleTy())
V = ConstantExpr::getBitCast(CFP, Type::getInt64Ty(V->getContext()));
// Don't handle long double formats, which have strange constraints.
}
// We can handle constant integers that are multiple of 8 bits.
if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) {
if (CI->getBitWidth() % 8 == 0) {
assert(CI->getBitWidth() > 8 && "8 bits should be handled above!");
// We can check that all bytes of an integer are equal by making use of a
// little trick: rotate by 8 and check if it's still the same value.
if (CI->getValue() != CI->getValue().rotl(8))
return nullptr;
return ConstantInt::get(V->getContext(), CI->getValue().trunc(8));
}
}
// A ConstantDataArray/Vector is splatable if all its members are equal and
// also splatable.
if (ConstantDataSequential *CA = dyn_cast<ConstantDataSequential>(V)) {
Value *Elt = CA->getElementAsConstant(0);
Value *Val = isBytewiseValue(Elt);
if (!Val)
return nullptr;
for (unsigned I = 1, E = CA->getNumElements(); I != E; ++I)
if (CA->getElementAsConstant(I) != Elt)
return nullptr;
return 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 nullptr;
}
// This is the recursive version of BuildSubAggregate. It takes a few different
// arguments. Idxs is the index within the nested struct From that we are
// looking at now (which is of type IndexedType). IdxSkip is the number of
// indices from Idxs that should be left out when inserting into the resulting
// struct. To is the result struct built so far, new insertvalue instructions
// build on that.
static Value *BuildSubAggregate(Value *From, Value* To, Type *IndexedType,
SmallVectorImpl<unsigned> &Idxs,
unsigned IdxSkip,
Instruction *InsertBefore) {
llvm::StructType *STy = dyn_cast<llvm::StructType>(IndexedType);
if (STy) {
// Save the original To argument so we can modify it
Value *OrigTo = To;
// General case, the type indexed by Idxs is a struct
for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
// Process each struct element recursively
Idxs.push_back(i);
Value *PrevTo = To;
To = BuildSubAggregate(From, To, STy->getElementType(i), Idxs, IdxSkip,
InsertBefore);
Idxs.pop_back();
if (!To) {
// Couldn't find any inserted value for this index? Cleanup
while (PrevTo != OrigTo) {
InsertValueInst* Del = cast<InsertValueInst>(PrevTo);
PrevTo = Del->getAggregateOperand();
Del->eraseFromParent();
}
// Stop processing elements
break;
}
}
// If we successfully found a value for each of our subaggregates
if (To)
return To;
}
// Base case, the type indexed by SourceIdxs is not a struct, or not all of
// the struct's elements had a value that was inserted directly. In the latter
// case, perhaps we can't determine each of the subelements individually, but
// we might be able to find the complete struct somewhere.
// Find the value that is at that particular spot
Value *V = FindInsertedValue(From, Idxs);
if (!V)
return nullptr;
// Insert the value in the new (sub) aggregrate
return llvm::InsertValueInst::Create(To, V, makeArrayRef(Idxs).slice(IdxSkip),
"tmp", InsertBefore);
}
// This helper takes a nested struct and extracts a part of it (which is again a
// struct) into a new value. For example, given the struct:
// { a, { b, { c, d }, e } }
// and the indices "1, 1" this returns
// { c, d }.
//
// It does this by inserting an insertvalue for each element in the resulting
// struct, as opposed to just inserting a single struct. This will only work if
// each of the elements of the substruct are known (ie, inserted into From by an
// insertvalue instruction somewhere).
//
// All inserted insertvalue instructions are inserted before InsertBefore
static Value *BuildSubAggregate(Value *From, ArrayRef<unsigned> idx_range,
Instruction *InsertBefore) {
assert(InsertBefore && "Must have someplace to insert!");
Type *IndexedType = ExtractValueInst::getIndexedType(From->getType(),
idx_range);
Value *To = UndefValue::get(IndexedType);
SmallVector<unsigned, 10> Idxs(idx_range.begin(), idx_range.end());
unsigned IdxSkip = Idxs.size();
return BuildSubAggregate(From, To, IndexedType, Idxs, IdxSkip, InsertBefore);
}
/// Given an aggregrate and an sequence of indices, see if
/// the scalar value indexed is already around as a register, for example if it
/// were inserted directly into the aggregrate.
///
/// If InsertBefore is not null, this function will duplicate (modified)
/// insertvalues when a part of a nested struct is extracted.
Value *llvm::FindInsertedValue(Value *V, ArrayRef<unsigned> idx_range,
Instruction *InsertBefore) {
// Nothing to index? Just return V then (this is useful at the end of our
// recursion).
if (idx_range.empty())
return V;
// We have indices, so V should have an indexable type.
assert((V->getType()->isStructTy() || V->getType()->isArrayTy()) &&
"Not looking at a struct or array?");
assert(ExtractValueInst::getIndexedType(V->getType(), idx_range) &&
"Invalid indices for type?");
if (Constant *C = dyn_cast<Constant>(V)) {
C = C->getAggregateElement(idx_range[0]);
if (!C) return nullptr;
return FindInsertedValue(C, idx_range.slice(1), InsertBefore);
}
if (InsertValueInst *I = dyn_cast<InsertValueInst>(V)) {
// Loop the indices for the insertvalue instruction in parallel with the
// requested indices
const unsigned *req_idx = idx_range.begin();
for (const unsigned *i = I->idx_begin(), *e = I->idx_end();
i != e; ++i, ++req_idx) {
if (req_idx == idx_range.end()) {
// We can't handle this without inserting insertvalues
if (!InsertBefore)
return nullptr;
// The requested index identifies a part of a nested aggregate. Handle
// this specially. For example,
// %A = insertvalue { i32, {i32, i32 } } undef, i32 10, 1, 0
// %B = insertvalue { i32, {i32, i32 } } %A, i32 11, 1, 1
// %C = extractvalue {i32, { i32, i32 } } %B, 1
// This can be changed into
// %A = insertvalue {i32, i32 } undef, i32 10, 0
// %C = insertvalue {i32, i32 } %A, i32 11, 1
// which allows the unused 0,0 element from the nested struct to be
// removed.
return BuildSubAggregate(V, makeArrayRef(idx_range.begin(), req_idx),
InsertBefore);
}
// This insert value inserts something else than what we are looking for.
// See if the (aggregrate) value inserted into has the value we are
// looking for, then.
if (*req_idx != *i)
return FindInsertedValue(I->getAggregateOperand(), idx_range,
InsertBefore);
}
// If we end up here, the indices of the insertvalue match with those
// requested (though possibly only partially). Now we recursively look at
// the inserted value, passing any remaining indices.
return FindInsertedValue(I->getInsertedValueOperand(),
makeArrayRef(req_idx, idx_range.end()),
InsertBefore);
}
if (ExtractValueInst *I = dyn_cast<ExtractValueInst>(V)) {
// If we're extracting a value from an aggregrate that was extracted from
// something else, we can extract from that something else directly instead.
// However, we will need to chain I's indices with the requested indices.
// Calculate the number of indices required
unsigned size = I->getNumIndices() + idx_range.size();
// Allocate some space to put the new indices in
SmallVector<unsigned, 5> Idxs;
Idxs.reserve(size);
// Add indices from the extract value instruction
Idxs.append(I->idx_begin(), I->idx_end());
// Add requested indices
Idxs.append(idx_range.begin(), idx_range.end());
assert(Idxs.size() == size
&& "Number of indices added not correct?");
return FindInsertedValue(I->getAggregateOperand(), Idxs, InsertBefore);
}
// Otherwise, we don't know (such as, extracting from a function return value
// or load instruction)
return nullptr;
}
/// Analyze the specified pointer to see if it can be expressed as a base
/// pointer plus a constant offset. Return the base and offset to the caller.
Value *llvm::GetPointerBaseWithConstantOffset(Value *Ptr, int64_t &Offset,
const DataLayout *DL) {
// Without DataLayout, conservatively assume 64-bit offsets, which is
// the widest we support.
unsigned BitWidth = DL ? DL->getPointerTypeSizeInBits(Ptr->getType()) : 64;
APInt ByteOffset(BitWidth, 0);
while (1) {
if (Ptr->getType()->isVectorTy())
break;
if (GEPOperator *GEP = dyn_cast<GEPOperator>(Ptr)) {
if (DL) {
APInt GEPOffset(BitWidth, 0);
if (!GEP->accumulateConstantOffset(*DL, GEPOffset))
break;
ByteOffset += GEPOffset;
}
Ptr = GEP->getPointerOperand();
} else if (Operator::getOpcode(Ptr) == Instruction::BitCast ||
Operator::getOpcode(Ptr) == Instruction::AddrSpaceCast) {
Ptr = cast<Operator>(Ptr)->getOperand(0);
} else if (GlobalAlias *GA = dyn_cast<GlobalAlias>(Ptr)) {
if (GA->mayBeOverridden())
break;
Ptr = GA->getAliasee();
} else {
break;
}
}
Offset = ByteOffset.getSExtValue();
return Ptr;
}
/// This function computes the length of a null-terminated C string pointed to
/// by V. If successful, it returns true and returns the string in Str.
/// If unsuccessful, it returns false.
bool llvm::getConstantStringInfo(const Value *V, StringRef &Str,
uint64_t Offset, bool TrimAtNul) {
assert(V);
// Look through bitcast instructions and geps.
V = V->stripPointerCasts();
// If the value is a GEP instructionor constant expression, treat it as an
// offset.
if (const GEPOperator *GEP = dyn_cast<GEPOperator>(V)) {
// Make sure the GEP has exactly three arguments.
if (GEP->getNumOperands() != 3)
return false;
// Make sure the index-ee is a pointer to array of i8.
PointerType *PT = cast<PointerType>(GEP->getOperand(0)->getType());
ArrayType *AT = dyn_cast<ArrayType>(PT->getElementType());
if (!AT || !AT->getElementType()->isIntegerTy(8))
return false;
// Check to make sure that the first operand of the GEP is an integer and
// has value 0 so that we are sure we're indexing into the initializer.
const ConstantInt *FirstIdx = dyn_cast<ConstantInt>(GEP->getOperand(1));
if (!FirstIdx || !FirstIdx->isZero())
return false;
// If the second index isn't a ConstantInt, then this is a variable index
// into the array. If this occurs, we can't say anything meaningful about
// the string.
uint64_t StartIdx = 0;
if (const ConstantInt *CI = dyn_cast<ConstantInt>(GEP->getOperand(2)))
StartIdx = CI->getZExtValue();
else
return false;
return getConstantStringInfo(GEP->getOperand(0), Str, StartIdx+Offset);
}
// The GEP instruction, constant or instruction, must reference a global
// variable that is a constant and is initialized. The referenced constant
// initializer is the array that we'll use for optimization.
const GlobalVariable *GV = dyn_cast<GlobalVariable>(V);
if (!GV || !GV->isConstant() || !GV->hasDefinitiveInitializer())
return false;
// Handle the all-zeros case
if (GV->getInitializer()->isNullValue()) {
// This is a degenerate case. The initializer is constant zero so the
// length of the string must be zero.
Str = "";
return true;
}
// Must be a Constant Array
const ConstantDataArray *Array =
dyn_cast<ConstantDataArray>(GV->getInitializer());
if (!Array || !Array->isString())
return false;
// Get the number of elements in the array
uint64_t NumElts = Array->getType()->getArrayNumElements();
// Start out with the entire array in the StringRef.
Str = Array->getAsString();
if (Offset > NumElts)
return false;
// Skip over 'offset' bytes.
Str = Str.substr(Offset);
if (TrimAtNul) {
// Trim off the \0 and anything after it. If the array is not nul
// terminated, we just return the whole end of string. The client may know
// some other way that the string is length-bound.
Str = Str.substr(0, Str.find('\0'));
}
return true;
}
// These next two are very similar to the above, but also look through PHI
// nodes.
// TODO: See if we can integrate these two together.
/// If we can compute the length of the string pointed to by
/// the specified pointer, return 'len+1'. If we can't, return 0.
static uint64_t GetStringLengthH(Value *V, SmallPtrSetImpl<PHINode*> &PHIs) {
// Look through noop bitcast instructions.
V = V->stripPointerCasts();
// If this is a PHI node, there are two cases: either we have already seen it
// or we haven't.
if (PHINode *PN = dyn_cast<PHINode>(V)) {
if (!PHIs.insert(PN).second)
return ~0ULL; // already in the set.
// If it was new, see if all the input strings are the same length.
uint64_t LenSoFar = ~0ULL;
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
uint64_t Len = GetStringLengthH(PN->getIncomingValue(i), PHIs);
if (Len == 0) return 0; // Unknown length -> unknown.
if (Len == ~0ULL) continue;
if (Len != LenSoFar && LenSoFar != ~0ULL)
return 0; // Disagree -> unknown.
LenSoFar = Len;
}
// Success, all agree.
return LenSoFar;
}
// strlen(select(c,x,y)) -> strlen(x) ^ strlen(y)
if (SelectInst *SI = dyn_cast<SelectInst>(V)) {
uint64_t Len1 = GetStringLengthH(SI->getTrueValue(), PHIs);
if (Len1 == 0) return 0;
uint64_t Len2 = GetStringLengthH(SI->getFalseValue(), PHIs);
if (Len2 == 0) return 0;
if (Len1 == ~0ULL) return Len2;
if (Len2 == ~0ULL) return Len1;
if (Len1 != Len2) return 0;
return Len1;
}
// Otherwise, see if we can read the string.
StringRef StrData;
if (!getConstantStringInfo(V, StrData))
return 0;
return StrData.size()+1;
}
/// If we can compute the length of the string pointed to by
/// the specified pointer, return 'len+1'. If we can't, return 0.
uint64_t llvm::GetStringLength(Value *V) {
if (!V->getType()->isPointerTy()) return 0;
SmallPtrSet<PHINode*, 32> PHIs;
uint64_t Len = GetStringLengthH(V, PHIs);
// If Len is ~0ULL, we had an infinite phi cycle: this is dead code, so return
// an empty string as a length.
return Len == ~0ULL ? 1 : Len;
}
Value *
llvm::GetUnderlyingObject(Value *V, const DataLayout *TD, unsigned MaxLookup) {
if (!V->getType()->isPointerTy())
return V;
for (unsigned Count = 0; MaxLookup == 0 || Count < MaxLookup; ++Count) {
if (GEPOperator *GEP = dyn_cast<GEPOperator>(V)) {
V = GEP->getPointerOperand();
} else if (Operator::getOpcode(V) == Instruction::BitCast ||
Operator::getOpcode(V) == Instruction::AddrSpaceCast) {
V = cast<Operator>(V)->getOperand(0);
} else if (GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) {
if (GA->mayBeOverridden())
return V;
V = GA->getAliasee();
} else {
// See if InstructionSimplify knows any relevant tricks.
if (Instruction *I = dyn_cast<Instruction>(V))
// TODO: Acquire a DominatorTree and AssumptionCache and use them.
if (Value *Simplified = SimplifyInstruction(I, TD, nullptr)) {
V = Simplified;
continue;
}
return V;
}
assert(V->getType()->isPointerTy() && "Unexpected operand type!");
}
return V;
}
void
llvm::GetUnderlyingObjects(Value *V,
SmallVectorImpl<Value *> &Objects,
const DataLayout *TD,
unsigned MaxLookup) {
SmallPtrSet<Value *, 4> Visited;
SmallVector<Value *, 4> Worklist;
Worklist.push_back(V);
do {
Value *P = Worklist.pop_back_val();
P = GetUnderlyingObject(P, TD, MaxLookup);
if (!Visited.insert(P).second)
continue;
if (SelectInst *SI = dyn_cast<SelectInst>(P)) {
Worklist.push_back(SI->getTrueValue());
Worklist.push_back(SI->getFalseValue());
continue;
}
if (PHINode *PN = dyn_cast<PHINode>(P)) {
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
Worklist.push_back(PN->getIncomingValue(i));
continue;
}
Objects.push_back(P);
} while (!Worklist.empty());
}
/// Return true if the only users of this pointer are lifetime markers.
bool llvm::onlyUsedByLifetimeMarkers(const Value *V) {
for (const User *U : V->users()) {
const IntrinsicInst *II = dyn_cast<IntrinsicInst>(U);
if (!II) return false;
if (II->getIntrinsicID() != Intrinsic::lifetime_start &&
II->getIntrinsicID() != Intrinsic::lifetime_end)
return false;
}
return true;
}
bool llvm::isSafeToSpeculativelyExecute(const Value *V,
const DataLayout *TD) {
const Operator *Inst = dyn_cast<Operator>(V);
if (!Inst)
return false;
for (unsigned i = 0, e = Inst->getNumOperands(); i != e; ++i)
if (Constant *C = dyn_cast<Constant>(Inst->getOperand(i)))
if (C->canTrap())
return false;
switch (Inst->getOpcode()) {
default:
return true;
case Instruction::UDiv:
case Instruction::URem: {
// x / y is undefined if y == 0.
const APInt *V;
if (match(Inst->getOperand(1), m_APInt(V)))
return *V != 0;
return false;
}
case Instruction::SDiv:
case Instruction::SRem: {
// x / y is undefined if y == 0 or x == INT_MIN and y == -1
const APInt *Numerator, *Denominator;
if (!match(Inst->getOperand(1), m_APInt(Denominator)))
return false;
// We cannot hoist this division if the denominator is 0.
if (*Denominator == 0)
return false;
// It's safe to hoist if the denominator is not 0 or -1.
if (*Denominator != -1)
return true;
// At this point we know that the denominator is -1. It is safe to hoist as
// long we know that the numerator is not INT_MIN.
if (match(Inst->getOperand(0), m_APInt(Numerator)))
return !Numerator->isMinSignedValue();
// The numerator *might* be MinSignedValue.
return false;
}
case Instruction::Load: {
const LoadInst *LI = cast<LoadInst>(Inst);
if (!LI->isUnordered() ||
// Speculative load may create a race that did not exist in the source.
LI->getParent()->getParent()->hasFnAttribute(Attribute::SanitizeThread))
return false;
return LI->getPointerOperand()->isDereferenceablePointer(TD);
}
case Instruction::Call: {
if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) {
switch (II->getIntrinsicID()) {
// These synthetic intrinsics have no side-effects and just mark
// information about their operands.
// FIXME: There are other no-op synthetic instructions that potentially
// should be considered at least *safe* to speculate...
case Intrinsic::dbg_declare:
case Intrinsic::dbg_value:
return true;
case Intrinsic::bswap:
case Intrinsic::ctlz:
case Intrinsic::ctpop:
case Intrinsic::cttz:
case Intrinsic::objectsize:
case Intrinsic::sadd_with_overflow:
case Intrinsic::smul_with_overflow:
case Intrinsic::ssub_with_overflow:
case Intrinsic::uadd_with_overflow:
case Intrinsic::umul_with_overflow:
case Intrinsic::usub_with_overflow:
return true;
// Sqrt should be OK, since the llvm sqrt intrinsic isn't defined to set
// errno like libm sqrt would.
case Intrinsic::sqrt:
case Intrinsic::fma:
case Intrinsic::fmuladd:
case Intrinsic::fabs:
case Intrinsic::minnum:
case Intrinsic::maxnum:
return true;
// TODO: some fp intrinsics are marked as having the same error handling
// as libm. They're safe to speculate when they won't error.
// TODO: are convert_{from,to}_fp16 safe?
// TODO: can we list target-specific intrinsics here?
default: break;
}
}
return false; // The called function could have undefined behavior or
// side-effects, even if marked readnone nounwind.
}
case Instruction::VAArg:
case Instruction::Alloca:
case Instruction::Invoke:
case Instruction::PHI:
case Instruction::Store:
case Instruction::Ret:
case Instruction::Br:
case Instruction::IndirectBr:
case Instruction::Switch:
case Instruction::Unreachable:
case Instruction::Fence:
case Instruction::LandingPad:
case Instruction::AtomicRMW:
case Instruction::AtomicCmpXchg:
case Instruction::Resume:
return false; // Misc instructions which have effects
}
}
/// Return true if we know that the specified value is never null.
bool llvm::isKnownNonNull(const Value *V, const TargetLibraryInfo *TLI) {
// Alloca never returns null, malloc might.
if (isa<AllocaInst>(V)) return true;
// A byval, inalloca, or nonnull argument is never null.
if (const Argument *A = dyn_cast<Argument>(V))
return A->hasByValOrInAllocaAttr() || A->hasNonNullAttr();
// Global values are not null unless extern weak.
if (const GlobalValue *GV = dyn_cast<GlobalValue>(V))
return !GV->hasExternalWeakLinkage();
// A Load tagged w/nonnull metadata is never null.
if (const LoadInst *LI = dyn_cast<LoadInst>(V))
return LI->getMetadata(LLVMContext::MD_nonnull);
if (ImmutableCallSite CS = V)
if (CS.isReturnNonNull())
return true;
// operator new never returns null.
if (isOperatorNewLikeFn(V, TLI, /*LookThroughBitCast=*/true))
return true;
return false;
}
OverflowResult llvm::computeOverflowForUnsignedMul(Value *LHS, Value *RHS,
const DataLayout *DL,
AssumptionCache *AC,
const Instruction *CxtI,
const DominatorTree *DT) {
// Multiplying n * m significant bits yields a result of n + m significant
// bits. If the total number of significant bits does not exceed the
// result bit width (minus 1), there is no overflow.
// This means if we have enough leading zero bits in the operands
// we can guarantee that the result does not overflow.
// Ref: "Hacker's Delight" by Henry Warren
unsigned BitWidth = LHS->getType()->getScalarSizeInBits();
APInt LHSKnownZero(BitWidth, 0);
APInt LHSKnownOne(BitWidth, 0);
APInt RHSKnownZero(BitWidth, 0);
APInt RHSKnownOne(BitWidth, 0);
computeKnownBits(LHS, LHSKnownZero, LHSKnownOne, DL, /*Depth=*/0, AC, CxtI,
DT);
computeKnownBits(RHS, RHSKnownZero, RHSKnownOne, DL, /*Depth=*/0, AC, CxtI,
DT);
// Note that underestimating the number of zero bits gives a more
// conservative answer.
unsigned ZeroBits = LHSKnownZero.countLeadingOnes() +
RHSKnownZero.countLeadingOnes();
// First handle the easy case: if we have enough zero bits there's
// definitely no overflow.
if (ZeroBits >= BitWidth)
return OverflowResult::NeverOverflows;
// Get the largest possible values for each operand.
APInt LHSMax = ~LHSKnownZero;
APInt RHSMax = ~RHSKnownZero;
// We know the multiply operation doesn't overflow if the maximum values for
// each operand will not overflow after we multiply them together.
bool MaxOverflow;
LHSMax.umul_ov(RHSMax, MaxOverflow);
if (!MaxOverflow)
return OverflowResult::NeverOverflows;
// We know it always overflows if multiplying the smallest possible values for
// the operands also results in overflow.
bool MinOverflow;
LHSKnownOne.umul_ov(RHSKnownOne, MinOverflow);
if (MinOverflow)
return OverflowResult::AlwaysOverflows;
return OverflowResult::MayOverflow;
}
OverflowResult llvm::computeOverflowForUnsignedAdd(Value *LHS, Value *RHS,
const DataLayout *DL,
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) {
// 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) {
// 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;
}
}
return OverflowResult::MayOverflow;
}
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