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llvm-project/llvm/lib/Analysis/ValueTracking.cpp

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//===- ValueTracking.cpp - Walk computations to compute properties --------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file contains routines that help analyze properties that chains of
// computations have.
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/ADT/APFloat.h"
#include "llvm/ADT/APInt.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/None.h"
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/iterator_range.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/AssumeBundleQueries.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/GuardUtils.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/Loads.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/OptimizationRemarkEmitter.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/IR/Argument.h"
#include "llvm/IR/Attributes.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/Constant.h"
#include "llvm/IR/ConstantRange.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/DiagnosticInfo.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/GetElementPtrTypeIterator.h"
#include "llvm/IR/GlobalAlias.h"
#include "llvm/IR/GlobalValue.h"
#include "llvm/IR/GlobalVariable.h"
#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/IntrinsicsAArch64.h"
#include "llvm/IR/IntrinsicsX86.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Metadata.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Operator.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/User.h"
#include "llvm/IR/Value.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/KnownBits.h"
#include "llvm/Support/MathExtras.h"
#include <algorithm>
#include <array>
#include <cassert>
#include <cstdint>
#include <iterator>
#include <utility>
using namespace llvm;
using namespace llvm::PatternMatch;
const unsigned MaxDepth = 6;
// Controls the number of uses of the value searched for possible
// dominating comparisons.
static cl::opt<unsigned> DomConditionsMaxUses("dom-conditions-max-uses",
cl::Hidden, cl::init(20));
/// Returns the bitwidth of the given scalar or pointer type. For vector types,
/// returns the element type's bitwidth.
static unsigned getBitWidth(Type *Ty, const DataLayout &DL) {
if (unsigned BitWidth = Ty->getScalarSizeInBits())
return BitWidth;
return DL.getPointerTypeSizeInBits(Ty);
}
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 {
const DataLayout &DL;
AssumptionCache *AC;
const Instruction *CxtI;
const DominatorTree *DT;
// Unlike the other analyses, this may be a nullptr because not all clients
// provide it currently.
OptimizationRemarkEmitter *ORE;
/// Set of assumptions that should be excluded from further queries.
/// 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 isKnownToBeAPowerOfTwo
/// (all of which can call computeKnownBits), and so on.
std::array<const Value *, MaxDepth> Excluded;
/// If true, it is safe to use metadata during simplification.
InstrInfoQuery IIQ;
unsigned NumExcluded = 0;
Query(const DataLayout &DL, AssumptionCache *AC, const Instruction *CxtI,
const DominatorTree *DT, bool UseInstrInfo,
OptimizationRemarkEmitter *ORE = nullptr)
: DL(DL), AC(AC), CxtI(CxtI), DT(DT), ORE(ORE), IIQ(UseInstrInfo) {}
Query(const Query &Q, const Value *NewExcl)
: DL(Q.DL), AC(Q.AC), CxtI(Q.CxtI), DT(Q.DT), ORE(Q.ORE), IIQ(Q.IIQ),
NumExcluded(Q.NumExcluded) {
Excluded = Q.Excluded;
Excluded[NumExcluded++] = NewExcl;
assert(NumExcluded <= Excluded.size());
}
bool isExcluded(const Value *Value) const {
if (NumExcluded == 0)
return false;
auto End = Excluded.begin() + NumExcluded;
return std::find(Excluded.begin(), End, Value) != End;
}
};
} // 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 bool getShuffleDemandedElts(const ShuffleVectorInst *Shuf,
const APInt &DemandedElts,
APInt &DemandedLHS, APInt &DemandedRHS) {
// The length of scalable vectors is unknown at compile time, thus we
// cannot check their values
if (isa<ScalableVectorType>(Shuf->getType()))
return false;
int NumElts =
cast<VectorType>(Shuf->getOperand(0)->getType())->getNumElements();
int NumMaskElts = Shuf->getType()->getNumElements();
DemandedLHS = DemandedRHS = APInt::getNullValue(NumElts);
if (DemandedElts.isNullValue())
return true;
// Simple case of a shuffle with zeroinitializer.
if (all_of(Shuf->getShuffleMask(), [](int Elt) { return Elt == 0; })) {
DemandedLHS.setBit(0);
return true;
}
for (int i = 0; i != NumMaskElts; ++i) {
if (!DemandedElts[i])
continue;
int M = Shuf->getMaskValue(i);
assert(M < (NumElts * 2) && "Invalid shuffle mask constant");
// For undef elements, we don't know anything about the common state of
// the shuffle result.
if (M == -1)
return false;
if (M < NumElts)
DemandedLHS.setBit(M % NumElts);
else
DemandedRHS.setBit(M % NumElts);
}
return true;
}
static void computeKnownBits(const Value *V, const APInt &DemandedElts,
KnownBits &Known, unsigned Depth, const Query &Q);
static void computeKnownBits(const Value *V, KnownBits &Known, unsigned Depth,
const Query &Q) {
// FIXME: We currently have no way to represent the DemandedElts of a scalable
// vector
if (isa<ScalableVectorType>(V->getType())) {
Known.resetAll();
return;
}
auto *FVTy = dyn_cast<FixedVectorType>(V->getType());
APInt DemandedElts =
FVTy ? APInt::getAllOnesValue(FVTy->getNumElements()) : APInt(1, 1);
computeKnownBits(V, DemandedElts, Known, Depth, Q);
}
void llvm::computeKnownBits(const Value *V, KnownBits &Known,
const DataLayout &DL, unsigned Depth,
AssumptionCache *AC, const Instruction *CxtI,
const DominatorTree *DT,
OptimizationRemarkEmitter *ORE, bool UseInstrInfo) {
::computeKnownBits(V, Known, Depth,
Query(DL, AC, safeCxtI(V, CxtI), DT, UseInstrInfo, ORE));
}
void llvm::computeKnownBits(const Value *V, const APInt &DemandedElts,
KnownBits &Known, const DataLayout &DL,
unsigned Depth, AssumptionCache *AC,
const Instruction *CxtI, const DominatorTree *DT,
OptimizationRemarkEmitter *ORE, bool UseInstrInfo) {
::computeKnownBits(V, DemandedElts, Known, Depth,
Query(DL, AC, safeCxtI(V, CxtI), DT, UseInstrInfo, ORE));
}
static KnownBits computeKnownBits(const Value *V, const APInt &DemandedElts,
unsigned Depth, const Query &Q);
static KnownBits computeKnownBits(const Value *V, unsigned Depth,
const Query &Q);
KnownBits llvm::computeKnownBits(const Value *V, const DataLayout &DL,
unsigned Depth, AssumptionCache *AC,
const Instruction *CxtI,
const DominatorTree *DT,
OptimizationRemarkEmitter *ORE,
bool UseInstrInfo) {
return ::computeKnownBits(
V, Depth, Query(DL, AC, safeCxtI(V, CxtI), DT, UseInstrInfo, ORE));
}
KnownBits llvm::computeKnownBits(const Value *V, const APInt &DemandedElts,
const DataLayout &DL, unsigned Depth,
AssumptionCache *AC, const Instruction *CxtI,
const DominatorTree *DT,
OptimizationRemarkEmitter *ORE,
bool UseInstrInfo) {
return ::computeKnownBits(
V, DemandedElts, Depth,
Query(DL, AC, safeCxtI(V, CxtI), DT, UseInstrInfo, ORE));
}
bool llvm::haveNoCommonBitsSet(const Value *LHS, const Value *RHS,
const DataLayout &DL, AssumptionCache *AC,
const Instruction *CxtI, const DominatorTree *DT,
bool UseInstrInfo) {
assert(LHS->getType() == RHS->getType() &&
"LHS and RHS should have the same type");
assert(LHS->getType()->isIntOrIntVectorTy() &&
"LHS and RHS should be integers");
// Look for an inverted mask: (X & ~M) op (Y & M).
Value *M;
if (match(LHS, m_c_And(m_Not(m_Value(M)), m_Value())) &&
match(RHS, m_c_And(m_Specific(M), m_Value())))
return true;
if (match(RHS, m_c_And(m_Not(m_Value(M)), m_Value())) &&
match(LHS, m_c_And(m_Specific(M), m_Value())))
return true;
IntegerType *IT = cast<IntegerType>(LHS->getType()->getScalarType());
KnownBits LHSKnown(IT->getBitWidth());
KnownBits RHSKnown(IT->getBitWidth());
computeKnownBits(LHS, LHSKnown, DL, 0, AC, CxtI, DT, nullptr, UseInstrInfo);
computeKnownBits(RHS, RHSKnown, DL, 0, AC, CxtI, DT, nullptr, UseInstrInfo);
return (LHSKnown.Zero | RHSKnown.Zero).isAllOnesValue();
}
bool llvm::isOnlyUsedInZeroEqualityComparison(const Instruction *CxtI) {
for (const User *U : CxtI->users()) {
if (const ICmpInst *IC = dyn_cast<ICmpInst>(U))
if (IC->isEquality())
if (Constant *C = dyn_cast<Constant>(IC->getOperand(1)))
if (C->isNullValue())
continue;
return false;
}
return true;
}
static bool isKnownToBeAPowerOfTwo(const Value *V, bool OrZero, unsigned Depth,
const Query &Q);
bool llvm::isKnownToBeAPowerOfTwo(const Value *V, const DataLayout &DL,
bool OrZero, unsigned Depth,
AssumptionCache *AC, const Instruction *CxtI,
const DominatorTree *DT, bool UseInstrInfo) {
return ::isKnownToBeAPowerOfTwo(
V, OrZero, Depth, Query(DL, AC, safeCxtI(V, CxtI), DT, UseInstrInfo));
}
static bool isKnownNonZero(const Value *V, const APInt &DemandedElts,
unsigned Depth, const Query &Q);
static bool isKnownNonZero(const Value *V, unsigned Depth, const Query &Q);
bool llvm::isKnownNonZero(const Value *V, const DataLayout &DL, unsigned Depth,
AssumptionCache *AC, const Instruction *CxtI,
const DominatorTree *DT, bool UseInstrInfo) {
return ::isKnownNonZero(V, Depth,
Query(DL, AC, safeCxtI(V, CxtI), DT, UseInstrInfo));
}
bool llvm::isKnownNonNegative(const Value *V, const DataLayout &DL,
unsigned Depth, AssumptionCache *AC,
const Instruction *CxtI, const DominatorTree *DT,
bool UseInstrInfo) {
KnownBits Known =
computeKnownBits(V, DL, Depth, AC, CxtI, DT, nullptr, UseInstrInfo);
return Known.isNonNegative();
}
bool llvm::isKnownPositive(const Value *V, const DataLayout &DL, unsigned Depth,
AssumptionCache *AC, const Instruction *CxtI,
const DominatorTree *DT, bool UseInstrInfo) {
if (auto *CI = dyn_cast<ConstantInt>(V))
return CI->getValue().isStrictlyPositive();
// TODO: We'd doing two recursive queries here. We should factor this such
// that only a single query is needed.
return isKnownNonNegative(V, DL, Depth, AC, CxtI, DT, UseInstrInfo) &&
isKnownNonZero(V, DL, Depth, AC, CxtI, DT, UseInstrInfo);
}
bool llvm::isKnownNegative(const Value *V, const DataLayout &DL, unsigned Depth,
AssumptionCache *AC, const Instruction *CxtI,
const DominatorTree *DT, bool UseInstrInfo) {
KnownBits Known =
computeKnownBits(V, DL, Depth, AC, CxtI, DT, nullptr, UseInstrInfo);
return Known.isNegative();
}
static bool isKnownNonEqual(const Value *V1, const Value *V2, const Query &Q);
bool llvm::isKnownNonEqual(const Value *V1, const Value *V2,
const DataLayout &DL, AssumptionCache *AC,
const Instruction *CxtI, const DominatorTree *DT,
bool UseInstrInfo) {
return ::isKnownNonEqual(V1, V2,
Query(DL, AC, safeCxtI(V1, safeCxtI(V2, CxtI)), DT,
UseInstrInfo, /*ORE=*/nullptr));
}
static bool MaskedValueIsZero(const Value *V, const APInt &Mask, unsigned Depth,
const Query &Q);
bool llvm::MaskedValueIsZero(const Value *V, const APInt &Mask,
const DataLayout &DL, unsigned Depth,
AssumptionCache *AC, const Instruction *CxtI,
const DominatorTree *DT, bool UseInstrInfo) {
return ::MaskedValueIsZero(
V, Mask, Depth, Query(DL, AC, safeCxtI(V, CxtI), DT, UseInstrInfo));
}
static unsigned ComputeNumSignBits(const Value *V, const APInt &DemandedElts,
unsigned Depth, const Query &Q);
static unsigned ComputeNumSignBits(const Value *V, unsigned Depth,
const Query &Q) {
// FIXME: We currently have no way to represent the DemandedElts of a scalable
// vector
if (isa<ScalableVectorType>(V->getType()))
return 1;
auto *FVTy = dyn_cast<FixedVectorType>(V->getType());
APInt DemandedElts =
FVTy ? APInt::getAllOnesValue(FVTy->getNumElements()) : APInt(1, 1);
return ComputeNumSignBits(V, DemandedElts, Depth, Q);
}
unsigned llvm::ComputeNumSignBits(const Value *V, const DataLayout &DL,
unsigned Depth, AssumptionCache *AC,
const Instruction *CxtI,
const DominatorTree *DT, bool UseInstrInfo) {
return ::ComputeNumSignBits(
V, Depth, Query(DL, AC, safeCxtI(V, CxtI), DT, UseInstrInfo));
}
static void computeKnownBitsAddSub(bool Add, const Value *Op0, const Value *Op1,
bool NSW, const APInt &DemandedElts,
KnownBits &KnownOut, KnownBits &Known2,
unsigned Depth, const Query &Q) {
computeKnownBits(Op1, DemandedElts, KnownOut, Depth + 1, Q);
// If one operand is unknown and we have no nowrap information,
// the result will be unknown independently of the second operand.
if (KnownOut.isUnknown() && !NSW)
return;
computeKnownBits(Op0, DemandedElts, Known2, Depth + 1, Q);
KnownOut = KnownBits::computeForAddSub(Add, NSW, Known2, KnownOut);
}
static void computeKnownBitsMul(const Value *Op0, const Value *Op1, bool NSW,
const APInt &DemandedElts, KnownBits &Known,
KnownBits &Known2, unsigned Depth,
const Query &Q) {
unsigned BitWidth = Known.getBitWidth();
computeKnownBits(Op1, DemandedElts, Known, Depth + 1, Q);
computeKnownBits(Op0, DemandedElts, Known2, 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 = Known.isNonNegative();
bool isKnownNonNegativeOp0 = Known2.isNonNegative();
bool isKnownNegativeOp1 = Known.isNegative();
bool isKnownNegativeOp0 = Known2.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, Depth, Q)) ||
(isKnownNegativeOp0 && isKnownNonNegativeOp1 &&
isKnownNonZero(Op1, Depth, Q));
}
}
assert(!Known.hasConflict() && !Known2.hasConflict());
// Compute a conservative estimate for high known-0 bits.
unsigned LeadZ = std::max(Known.countMinLeadingZeros() +
Known2.countMinLeadingZeros(),
BitWidth) - BitWidth;
LeadZ = std::min(LeadZ, BitWidth);
// The result of the bottom bits of an integer multiply can be
// inferred by looking at the bottom bits of both operands and
// multiplying them together.
// We can infer at least the minimum number of known trailing bits
// of both operands. Depending on number of trailing zeros, we can
// infer more bits, because (a*b) <=> ((a/m) * (b/n)) * (m*n) assuming
// a and b are divisible by m and n respectively.
// We then calculate how many of those bits are inferrable and set
// the output. For example, the i8 mul:
// a = XXXX1100 (12)
// b = XXXX1110 (14)
// We know the bottom 3 bits are zero since the first can be divided by
// 4 and the second by 2, thus having ((12/4) * (14/2)) * (2*4).
// Applying the multiplication to the trimmed arguments gets:
// XX11 (3)
// X111 (7)
// -------
// XX11
// XX11
// XX11
// XX11
// -------
// XXXXX01
// Which allows us to infer the 2 LSBs. Since we're multiplying the result
// by 8, the bottom 3 bits will be 0, so we can infer a total of 5 bits.
// The proof for this can be described as:
// Pre: (C1 >= 0) && (C1 < (1 << C5)) && (C2 >= 0) && (C2 < (1 << C6)) &&
// (C7 == (1 << (umin(countTrailingZeros(C1), C5) +
// umin(countTrailingZeros(C2), C6) +
// umin(C5 - umin(countTrailingZeros(C1), C5),
// C6 - umin(countTrailingZeros(C2), C6)))) - 1)
// %aa = shl i8 %a, C5
// %bb = shl i8 %b, C6
// %aaa = or i8 %aa, C1
// %bbb = or i8 %bb, C2
// %mul = mul i8 %aaa, %bbb
// %mask = and i8 %mul, C7
// =>
// %mask = i8 ((C1*C2)&C7)
// Where C5, C6 describe the known bits of %a, %b
// C1, C2 describe the known bottom bits of %a, %b.
// C7 describes the mask of the known bits of the result.
APInt Bottom0 = Known.One;
APInt Bottom1 = Known2.One;
// How many times we'd be able to divide each argument by 2 (shr by 1).
// This gives us the number of trailing zeros on the multiplication result.
unsigned TrailBitsKnown0 = (Known.Zero | Known.One).countTrailingOnes();
unsigned TrailBitsKnown1 = (Known2.Zero | Known2.One).countTrailingOnes();
unsigned TrailZero0 = Known.countMinTrailingZeros();
unsigned TrailZero1 = Known2.countMinTrailingZeros();
unsigned TrailZ = TrailZero0 + TrailZero1;
// Figure out the fewest known-bits operand.
unsigned SmallestOperand = std::min(TrailBitsKnown0 - TrailZero0,
TrailBitsKnown1 - TrailZero1);
unsigned ResultBitsKnown = std::min(SmallestOperand + TrailZ, BitWidth);
APInt BottomKnown = Bottom0.getLoBits(TrailBitsKnown0) *
Bottom1.getLoBits(TrailBitsKnown1);
Known.resetAll();
Known.Zero.setHighBits(LeadZ);
Known.Zero |= (~BottomKnown).getLoBits(ResultBitsKnown);
Known.One |= BottomKnown.getLoBits(ResultBitsKnown);
// 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 && !Known.isNegative())
Known.makeNonNegative();
else if (isKnownNegative && !Known.isNonNegative())
Known.makeNegative();
}
void llvm::computeKnownBitsFromRangeMetadata(const MDNode &Ranges,
KnownBits &Known) {
unsigned BitWidth = Known.getBitWidth();
unsigned NumRanges = Ranges.getNumOperands() / 2;
assert(NumRanges >= 1);
Known.Zero.setAllBits();
Known.One.setAllBits();
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());
// The first CommonPrefixBits of all values in Range are equal.
unsigned CommonPrefixBits =
(Range.getUnsignedMax() ^ Range.getUnsignedMin()).countLeadingZeros();
APInt Mask = APInt::getHighBitsSet(BitWidth, CommonPrefixBits);
Known.One &= Range.getUnsignedMax() & Mask;
Known.Zero &= ~Range.getUnsignedMax() & Mask;
}
}
static bool isEphemeralValueOf(const Instruction *I, const Value *E) {
SmallVector<const Value *, 16> WorkSet(1, I);
SmallPtrSet<const Value *, 32> Visited;
SmallPtrSet<const Value *, 16> EphValues;
// The instruction defining an assumption's condition itself is always
// considered ephemeral to that assumption (even if it has other
// non-ephemeral users). See r246696's test case for an example.
if (is_contained(I->operands(), E))
return true;
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.
if (llvm::all_of(V->users(), [&](const User *U) {
return EphValues.count(U);
})) {
if (V == E)
return true;
if (V == I || isSafeToSpeculativelyExecute(V)) {
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)
WorkSet.push_back(*J);
}
}
}
return false;
}
// Is this an intrinsic that cannot be speculated but also cannot trap?
bool llvm::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::sideeffect:
case Intrinsic::dbg_declare:
case Intrinsic::dbg_value:
case Intrinsic::dbg_label:
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;
}
bool llvm::isValidAssumeForContext(const Instruction *Inv,
const Instruction *CxtI,
const DominatorTree *DT) {
// 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 (Inv->getParent() == CxtI->getParent()) {
// If Inv and CtxI are in the same block, check if the assume (Inv) is first
// in the BB.
if (Inv->comesBefore(CxtI))
return true;
// Don't let an assume affect itself - this would cause the problems
// `isEphemeralValueOf` is trying to prevent, and it would also make
// the loop below go out of bounds.
if (Inv == CxtI)
return false;
// 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, not even CxtI itself.
for (BasicBlock::const_iterator I(CxtI), IE(Inv); I != IE; ++I)
if (!isGuaranteedToTransferExecutionToSuccessor(&*I))
return false;
return !isEphemeralValueOf(Inv, CxtI);
}
// Inv and CxtI are in different blocks.
if (DT) {
if (DT->dominates(Inv, CxtI))
return true;
} else if (Inv->getParent() == CxtI->getParent()->getSinglePredecessor()) {
// We don't have a DT, but this trivially dominates.
return true;
}
return false;
}
static bool isKnownNonZeroFromAssume(const Value *V, 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 false;
// Note that the patterns below need to be kept in sync with the code
// in AssumptionCache::updateAffectedValues.
auto CmpExcludesZero = [V](ICmpInst *Cmp) {
auto m_V = m_CombineOr(m_Specific(V), m_PtrToInt(m_Specific(V)));
Value *RHS;
CmpInst::Predicate Pred;
if (!match(Cmp, m_c_ICmp(Pred, m_V, m_Value(RHS))))
return false;
// assume(v u> y) -> assume(v != 0)
if (Pred == ICmpInst::ICMP_UGT)
return true;
// assume(v != 0)
// We special-case this one to ensure that we handle `assume(v != null)`.
if (Pred == ICmpInst::ICMP_NE)
return match(RHS, m_Zero());
// All other predicates - rely on generic ConstantRange handling.
ConstantInt *CI;
if (!match(RHS, m_ConstantInt(CI)))
return false;
ConstantRange RHSRange(CI->getValue());
ConstantRange TrueValues =
ConstantRange::makeAllowedICmpRegion(Pred, RHSRange);
return !TrueValues.contains(APInt::getNullValue(CI->getBitWidth()));
};
if (Q.CxtI && V->getType()->isPointerTy()) {
SmallVector<Attribute::AttrKind, 2> AttrKinds{Attribute::NonNull};
if (!NullPointerIsDefined(Q.CxtI->getFunction(),
V->getType()->getPointerAddressSpace()))
AttrKinds.push_back(Attribute::Dereferenceable);
if (getKnowledgeValidInContext(V, AttrKinds, Q.CxtI, Q.DT, Q.AC))
return true;
}
for (auto &AssumeVH : Q.AC->assumptionsFor(V)) {
if (!AssumeVH)
continue;
CallInst *I = cast<CallInst>(AssumeVH);
assert(I->getFunction() == Q.CxtI->getFunction() &&
"Got assumption for the wrong function!");
if (Q.isExcluded(I))
continue;
// Warning: This loop can end up being somewhat performance sensitive.
// We're running this loop for once for each value queried resulting in a
// runtime of ~O(#assumes * #values).
assert(I->getCalledFunction()->getIntrinsicID() == Intrinsic::assume &&
"must be an assume intrinsic");
Value *Arg = I->getArgOperand(0);
ICmpInst *Cmp = dyn_cast<ICmpInst>(Arg);
if (!Cmp)
continue;
if (CmpExcludesZero(Cmp) && isValidAssumeForContext(I, Q.CxtI, Q.DT))
return true;
}
return false;
}
static void computeKnownBitsFromAssume(const Value *V, KnownBits &Known,
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 = Known.getBitWidth();
// Note that the patterns below need to be kept in sync with the code
// in AssumptionCache::updateAffectedValues.
for (auto &AssumeVH : Q.AC->assumptionsFor(V)) {
if (!AssumeVH)
continue;
CallInst *I = cast<CallInst>(AssumeVH);
assert(I->getParent()->getParent() == Q.CxtI->getParent()->getParent() &&
"Got assumption for the wrong function!");
if (Q.isExcluded(I))
continue;
// Warning: This loop can end up being somewhat performance sensitive.
// We're running this loop for once for each value queried resulting in a
// runtime of ~O(#assumes * #values).
assert(I->getCalledFunction()->getIntrinsicID() == Intrinsic::assume &&
"must be an assume intrinsic");
Value *Arg = I->getArgOperand(0);
if (Arg == V && isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
assert(BitWidth == 1 && "assume operand is not i1?");
Known.setAllOnes();
return;
}
if (match(Arg, m_Not(m_Specific(V))) &&
isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
assert(BitWidth == 1 && "assume operand is not i1?");
Known.setAllZero();
return;
}
// The remaining tests are all recursive, so bail out if we hit the limit.
if (Depth == MaxDepth)
continue;
ICmpInst *Cmp = dyn_cast<ICmpInst>(Arg);
if (!Cmp)
continue;
// Note that ptrtoint may change the bitwidth.
Value *A, *B;
auto m_V = m_CombineOr(m_Specific(V), m_PtrToInt(m_Specific(V)));
CmpInst::Predicate Pred;
uint64_t C;
switch (Cmp->getPredicate()) {
default:
break;
case ICmpInst::ICMP_EQ:
// assume(v = a)
if (match(Cmp, m_c_ICmp(Pred, m_V, m_Value(A))) &&
isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
KnownBits RHSKnown =
computeKnownBits(A, Depth+1, Query(Q, I)).anyextOrTrunc(BitWidth);
Known.Zero |= RHSKnown.Zero;
Known.One |= RHSKnown.One;
// assume(v & b = a)
} else if (match(Cmp,
m_c_ICmp(Pred, m_c_And(m_V, m_Value(B)), m_Value(A))) &&
isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
KnownBits RHSKnown =
computeKnownBits(A, Depth+1, Query(Q, I)).anyextOrTrunc(BitWidth);
KnownBits MaskKnown =
computeKnownBits(B, Depth+1, Query(Q, I)).anyextOrTrunc(BitWidth);
// For those bits in the mask that are known to be one, we can propagate
// known bits from the RHS to V.
Known.Zero |= RHSKnown.Zero & MaskKnown.One;
Known.One |= RHSKnown.One & MaskKnown.One;
// assume(~(v & b) = a)
} else if (match(Cmp, m_c_ICmp(Pred, m_Not(m_c_And(m_V, m_Value(B))),
m_Value(A))) &&
isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
KnownBits RHSKnown =
computeKnownBits(A, Depth+1, Query(Q, I)).anyextOrTrunc(BitWidth);
KnownBits MaskKnown =
computeKnownBits(B, Depth+1, Query(Q, I)).anyextOrTrunc(BitWidth);
// For those bits in the mask that are known to be one, we can propagate
// inverted known bits from the RHS to V.
Known.Zero |= RHSKnown.One & MaskKnown.One;
Known.One |= RHSKnown.Zero & MaskKnown.One;
// assume(v | b = a)
} else if (match(Cmp,
m_c_ICmp(Pred, m_c_Or(m_V, m_Value(B)), m_Value(A))) &&
isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
KnownBits RHSKnown =
computeKnownBits(A, Depth+1, Query(Q, I)).anyextOrTrunc(BitWidth);
KnownBits BKnown =
computeKnownBits(B, Depth+1, Query(Q, I)).anyextOrTrunc(BitWidth);
// For those bits in B that are known to be zero, we can propagate known
// bits from the RHS to V.
Known.Zero |= RHSKnown.Zero & BKnown.Zero;
Known.One |= RHSKnown.One & BKnown.Zero;
// assume(~(v | b) = a)
} else if (match(Cmp, m_c_ICmp(Pred, m_Not(m_c_Or(m_V, m_Value(B))),
m_Value(A))) &&
isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
KnownBits RHSKnown =
computeKnownBits(A, Depth+1, Query(Q, I)).anyextOrTrunc(BitWidth);
KnownBits BKnown =
computeKnownBits(B, Depth+1, Query(Q, I)).anyextOrTrunc(BitWidth);
// For those bits in B that are known to be zero, we can propagate
// inverted known bits from the RHS to V.
Known.Zero |= RHSKnown.One & BKnown.Zero;
Known.One |= RHSKnown.Zero & BKnown.Zero;
// assume(v ^ b = a)
} else if (match(Cmp,
m_c_ICmp(Pred, m_c_Xor(m_V, m_Value(B)), m_Value(A))) &&
isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
KnownBits RHSKnown =
computeKnownBits(A, Depth+1, Query(Q, I)).anyextOrTrunc(BitWidth);
KnownBits BKnown =
computeKnownBits(B, Depth+1, Query(Q, I)).anyextOrTrunc(BitWidth);
// 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.
Known.Zero |= RHSKnown.Zero & BKnown.Zero;
Known.One |= RHSKnown.One & BKnown.Zero;
Known.Zero |= RHSKnown.One & BKnown.One;
Known.One |= RHSKnown.Zero & BKnown.One;
// assume(~(v ^ b) = a)
} else if (match(Cmp, m_c_ICmp(Pred, m_Not(m_c_Xor(m_V, m_Value(B))),
m_Value(A))) &&
isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
KnownBits RHSKnown =
computeKnownBits(A, Depth+1, Query(Q, I)).anyextOrTrunc(BitWidth);
KnownBits BKnown =
computeKnownBits(B, Depth+1, Query(Q, I)).anyextOrTrunc(BitWidth);
// 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.
Known.Zero |= RHSKnown.One & BKnown.Zero;
Known.One |= RHSKnown.Zero & BKnown.Zero;
Known.Zero |= RHSKnown.Zero & BKnown.One;
Known.One |= RHSKnown.One & BKnown.One;
// assume(v << c = a)
} else if (match(Cmp, m_c_ICmp(Pred, m_Shl(m_V, m_ConstantInt(C)),
m_Value(A))) &&
isValidAssumeForContext(I, Q.CxtI, Q.DT) && C < BitWidth) {
KnownBits RHSKnown =
computeKnownBits(A, Depth+1, Query(Q, I)).anyextOrTrunc(BitWidth);
// For those bits in RHS that are known, we can propagate them to known
// bits in V shifted to the right by C.
RHSKnown.Zero.lshrInPlace(C);
Known.Zero |= RHSKnown.Zero;
RHSKnown.One.lshrInPlace(C);
Known.One |= RHSKnown.One;
// assume(~(v << c) = a)
} else if (match(Cmp, m_c_ICmp(Pred, m_Not(m_Shl(m_V, m_ConstantInt(C))),
m_Value(A))) &&
isValidAssumeForContext(I, Q.CxtI, Q.DT) && C < BitWidth) {
KnownBits RHSKnown =
computeKnownBits(A, Depth+1, Query(Q, I)).anyextOrTrunc(BitWidth);
// For those bits in RHS that are known, we can propagate them inverted
// to known bits in V shifted to the right by C.
RHSKnown.One.lshrInPlace(C);
Known.Zero |= RHSKnown.One;
RHSKnown.Zero.lshrInPlace(C);
Known.One |= RHSKnown.Zero;
// assume(v >> c = a)
} else if (match(Cmp, m_c_ICmp(Pred, m_Shr(m_V, m_ConstantInt(C)),
m_Value(A))) &&
isValidAssumeForContext(I, Q.CxtI, Q.DT) && C < BitWidth) {
KnownBits RHSKnown =
computeKnownBits(A, Depth+1, Query(Q, I)).anyextOrTrunc(BitWidth);
// For those bits in RHS that are known, we can propagate them to known
// bits in V shifted to the right by C.
Known.Zero |= RHSKnown.Zero << C;
Known.One |= RHSKnown.One << C;
// assume(~(v >> c) = a)
} else if (match(Cmp, m_c_ICmp(Pred, m_Not(m_Shr(m_V, m_ConstantInt(C))),
m_Value(A))) &&
isValidAssumeForContext(I, Q.CxtI, Q.DT) && C < BitWidth) {
KnownBits RHSKnown =
computeKnownBits(A, Depth+1, Query(Q, I)).anyextOrTrunc(BitWidth);
// For those bits in RHS that are known, we can propagate them inverted
// to known bits in V shifted to the right by C.
Known.Zero |= RHSKnown.One << C;
Known.One |= RHSKnown.Zero << C;
}
break;
case ICmpInst::ICMP_SGE:
// assume(v >=_s c) where c is non-negative
if (match(Cmp, m_ICmp(Pred, m_V, m_Value(A))) &&
isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
KnownBits RHSKnown =
computeKnownBits(A, Depth + 1, Query(Q, I)).anyextOrTrunc(BitWidth);
if (RHSKnown.isNonNegative()) {
// We know that the sign bit is zero.
Known.makeNonNegative();
}
}
break;
case ICmpInst::ICMP_SGT:
// assume(v >_s c) where c is at least -1.
if (match(Cmp, m_ICmp(Pred, m_V, m_Value(A))) &&
isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
KnownBits RHSKnown =
computeKnownBits(A, Depth + 1, Query(Q, I)).anyextOrTrunc(BitWidth);
if (RHSKnown.isAllOnes() || RHSKnown.isNonNegative()) {
// We know that the sign bit is zero.
Known.makeNonNegative();
}
}
break;
case ICmpInst::ICMP_SLE:
// assume(v <=_s c) where c is negative
if (match(Cmp, m_ICmp(Pred, m_V, m_Value(A))) &&
isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
KnownBits RHSKnown =
computeKnownBits(A, Depth + 1, Query(Q, I)).anyextOrTrunc(BitWidth);
if (RHSKnown.isNegative()) {
// We know that the sign bit is one.
Known.makeNegative();
}
}
break;
case ICmpInst::ICMP_SLT:
// assume(v <_s c) where c is non-positive
if (match(Cmp, m_ICmp(Pred, m_V, m_Value(A))) &&
isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
KnownBits RHSKnown =
computeKnownBits(A, Depth+1, Query(Q, I)).anyextOrTrunc(BitWidth);
if (RHSKnown.isZero() || RHSKnown.isNegative()) {
// We know that the sign bit is one.
Known.makeNegative();
}
}
break;
case ICmpInst::ICMP_ULE:
// assume(v <=_u c)
if (match(Cmp, m_ICmp(Pred, m_V, m_Value(A))) &&
isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
KnownBits RHSKnown =
computeKnownBits(A, Depth+1, Query(Q, I)).anyextOrTrunc(BitWidth);
// Whatever high bits in c are zero are known to be zero.
Known.Zero.setHighBits(RHSKnown.countMinLeadingZeros());
}
break;
case ICmpInst::ICMP_ULT:
// assume(v <_u c)
if (match(Cmp, m_ICmp(Pred, m_V, m_Value(A))) &&
isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
KnownBits RHSKnown =
computeKnownBits(A, Depth+1, Query(Q, I)).anyextOrTrunc(BitWidth);
// If the RHS is known zero, then this assumption must be wrong (nothing
// is unsigned less than zero). Signal a conflict and get out of here.
if (RHSKnown.isZero()) {
Known.Zero.setAllBits();
Known.One.setAllBits();
break;
}
// Whatever high bits in c are zero are known to be zero (if c is a power
// of 2, then one more).
if (isKnownToBeAPowerOfTwo(A, false, Depth + 1, Query(Q, I)))
Known.Zero.setHighBits(RHSKnown.countMinLeadingZeros() + 1);
else
Known.Zero.setHighBits(RHSKnown.countMinLeadingZeros());
}
break;
}
}
// If assumptions conflict with each other or previous known bits, then we
// have a logical fallacy. It's possible that the assumption is not reachable,
// so this isn't a real bug. On the other hand, the program may have undefined
// behavior, or we might have a bug in the compiler. We can't assert/crash, so
// clear out the known bits, try to warn the user, and hope for the best.
if (Known.Zero.intersects(Known.One)) {
Known.resetAll();
if (Q.ORE)
Q.ORE->emit([&]() {
auto *CxtI = const_cast<Instruction *>(Q.CxtI);
return OptimizationRemarkAnalysis("value-tracking", "BadAssumption",
CxtI)
<< "Detected conflicting code assumptions. Program may "
"have undefined behavior, or compiler may have "
"internal error.";
});
}
}
/// Compute known bits from a shift operator, including those with a
/// non-constant shift amount. Known is the output of this function. Known2 is a
/// pre-allocated temporary with the same bit width as Known. KZF and KOF are
/// operator-specific functions that, given the known-zero or known-one bits
/// respectively, and a shift amount, compute the implied known-zero or
/// known-one bits of the shift operator's result respectively for that shift
/// amount. The results from calling KZF and KOF are conservatively combined for
/// all permitted shift amounts.
static void computeKnownBitsFromShiftOperator(
const Operator *I, const APInt &DemandedElts, KnownBits &Known,
KnownBits &Known2, unsigned Depth, const Query &Q,
function_ref<APInt(const APInt &, unsigned)> KZF,
function_ref<APInt(const APInt &, unsigned)> KOF) {
unsigned BitWidth = Known.getBitWidth();
computeKnownBits(I->getOperand(1), DemandedElts, Known, Depth + 1, Q);
if (Known.isConstant()) {
unsigned ShiftAmt = Known.getConstant().getLimitedValue(BitWidth - 1);
computeKnownBits(I->getOperand(0), DemandedElts, Known, Depth + 1, Q);
Known.Zero = KZF(Known.Zero, ShiftAmt);
Known.One = KOF(Known.One, ShiftAmt);
// If the known bits conflict, this must be an overflowing left shift, so
// the shift result is poison. We can return anything we want. Choose 0 for
// the best folding opportunity.
if (Known.hasConflict())
Known.setAllZero();
return;
}
// If the shift amount could be greater than or equal to the bit-width of the
// LHS, the value could be poison, but bail out because the check below is
// expensive.
// TODO: Should we just carry on?
if (Known.getMaxValue().uge(BitWidth)) {
Known.resetAll();
return;
}
// Note: We cannot use Known.Zero.getLimitedValue() here, because if
// BitWidth > 64 and any upper bits are known, we'll end up returning the
// limit value (which implies all bits are known).
uint64_t ShiftAmtKZ = Known.Zero.zextOrTrunc(64).getZExtValue();
uint64_t ShiftAmtKO = Known.One.zextOrTrunc(64).getZExtValue();
// It would be more-clearly correct to use the two temporaries for this
// calculation. Reusing the APInts here to prevent unnecessary allocations.
Known.resetAll();
// If we know the shifter operand is nonzero, we can sometimes infer more
// known bits. However this is expensive to compute, so be lazy about it and
// only compute it when absolutely necessary.
Optional<bool> ShifterOperandIsNonZero;
// Early exit if we can't constrain any well-defined shift amount.
if (!(ShiftAmtKZ & (PowerOf2Ceil(BitWidth) - 1)) &&
!(ShiftAmtKO & (PowerOf2Ceil(BitWidth) - 1))) {
ShifterOperandIsNonZero =
isKnownNonZero(I->getOperand(1), DemandedElts, Depth + 1, Q);
if (!*ShifterOperandIsNonZero)
return;
}
computeKnownBits(I->getOperand(0), DemandedElts, Known2, Depth + 1, Q);
Known.Zero.setAllBits();
Known.One.setAllBits();
for (unsigned ShiftAmt = 0; ShiftAmt < BitWidth; ++ShiftAmt) {
// Combine the shifted known input bits only for those shift amounts
// compatible with its known constraints.
if ((ShiftAmt & ~ShiftAmtKZ) != ShiftAmt)
continue;
if ((ShiftAmt | ShiftAmtKO) != ShiftAmt)
continue;
// If we know the shifter is nonzero, we may be able to infer more known
// bits. This check is sunk down as far as possible to avoid the expensive
// call to isKnownNonZero if the cheaper checks above fail.
if (ShiftAmt == 0) {
if (!ShifterOperandIsNonZero.hasValue())
ShifterOperandIsNonZero =
isKnownNonZero(I->getOperand(1), DemandedElts, Depth + 1, Q);
if (*ShifterOperandIsNonZero)
continue;
}
Known.Zero &= KZF(Known2.Zero, ShiftAmt);
Known.One &= KOF(Known2.One, ShiftAmt);
}
// If the known bits conflict, the result is poison. Return a 0 and hope the
// caller can further optimize that.
if (Known.hasConflict())
Known.setAllZero();
}
static void computeKnownBitsFromOperator(const Operator *I,
const APInt &DemandedElts,
KnownBits &Known, unsigned Depth,
const Query &Q) {
unsigned BitWidth = Known.getBitWidth();
KnownBits Known2(BitWidth);
switch (I->getOpcode()) {
default: break;
case Instruction::Load:
if (MDNode *MD =
Q.IIQ.getMetadata(cast<LoadInst>(I), LLVMContext::MD_range))
computeKnownBitsFromRangeMetadata(*MD, Known);
break;
case Instruction::And: {
// If either the LHS or the RHS are Zero, the result is zero.
computeKnownBits(I->getOperand(1), DemandedElts, Known, Depth + 1, Q);
computeKnownBits(I->getOperand(0), DemandedElts, Known2, Depth + 1, Q);
Known &= Known2;
// and(x, add (x, -1)) is a common idiom that always clears the low bit;
// here we handle the more general case of adding any odd number by
// matching the form add(x, add(x, y)) where y is odd.
// TODO: This could be generalized to clearing any bit set in y where the
// following bit is known to be unset in y.
Value *X = nullptr, *Y = nullptr;
if (!Known.Zero[0] && !Known.One[0] &&
match(I, m_c_BinOp(m_Value(X), m_Add(m_Deferred(X), m_Value(Y))))) {
Known2.resetAll();
computeKnownBits(Y, DemandedElts, Known2, Depth + 1, Q);
if (Known2.countMinTrailingOnes() > 0)
Known.Zero.setBit(0);
}
break;
}
case Instruction::Or:
computeKnownBits(I->getOperand(1), DemandedElts, Known, Depth + 1, Q);
computeKnownBits(I->getOperand(0), DemandedElts, Known2, Depth + 1, Q);
Known |= Known2;
break;
case Instruction::Xor:
computeKnownBits(I->getOperand(1), DemandedElts, Known, Depth + 1, Q);
computeKnownBits(I->getOperand(0), DemandedElts, Known2, Depth + 1, Q);
Known ^= Known2;
break;
case Instruction::Mul: {
bool NSW = Q.IIQ.hasNoSignedWrap(cast<OverflowingBinaryOperator>(I));
computeKnownBitsMul(I->getOperand(0), I->getOperand(1), NSW, DemandedElts,
Known, Known2, 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), Known2, Depth + 1, Q);
unsigned LeadZ = Known2.countMinLeadingZeros();
Known2.resetAll();
computeKnownBits(I->getOperand(1), Known2, Depth + 1, Q);
unsigned RHSMaxLeadingZeros = Known2.countMaxLeadingZeros();
if (RHSMaxLeadingZeros != BitWidth)
LeadZ = std::min(BitWidth, LeadZ + BitWidth - RHSMaxLeadingZeros - 1);
Known.Zero.setHighBits(LeadZ);
break;
}
case Instruction::Select: {
const Value *LHS = nullptr, *RHS = nullptr;
SelectPatternFlavor SPF = matchSelectPattern(I, LHS, RHS).Flavor;
if (SelectPatternResult::isMinOrMax(SPF)) {
computeKnownBits(RHS, Known, Depth + 1, Q);
computeKnownBits(LHS, Known2, Depth + 1, Q);
} else {
computeKnownBits(I->getOperand(2), Known, Depth + 1, Q);
computeKnownBits(I->getOperand(1), Known2, Depth + 1, Q);
}
unsigned MaxHighOnes = 0;
unsigned MaxHighZeros = 0;
if (SPF == SPF_SMAX) {
// If both sides are negative, the result is negative.
if (Known.isNegative() && Known2.isNegative())
// We can derive a lower bound on the result by taking the max of the
// leading one bits.
MaxHighOnes =
std::max(Known.countMinLeadingOnes(), Known2.countMinLeadingOnes());
// If either side is non-negative, the result is non-negative.
else if (Known.isNonNegative() || Known2.isNonNegative())
MaxHighZeros = 1;
} else if (SPF == SPF_SMIN) {
// If both sides are non-negative, the result is non-negative.
if (Known.isNonNegative() && Known2.isNonNegative())
// We can derive an upper bound on the result by taking the max of the
// leading zero bits.
MaxHighZeros = std::max(Known.countMinLeadingZeros(),
Known2.countMinLeadingZeros());
// If either side is negative, the result is negative.
else if (Known.isNegative() || Known2.isNegative())
MaxHighOnes = 1;
} else if (SPF == SPF_UMAX) {
// We can derive a lower bound on the result by taking the max of the
// leading one bits.
MaxHighOnes =
std::max(Known.countMinLeadingOnes(), Known2.countMinLeadingOnes());
} else if (SPF == SPF_UMIN) {
// We can derive an upper bound on the result by taking the max of the
// leading zero bits.
MaxHighZeros =
std::max(Known.countMinLeadingZeros(), Known2.countMinLeadingZeros());
} else if (SPF == SPF_ABS) {
// RHS from matchSelectPattern returns the negation part of abs pattern.
// If the negate has an NSW flag we can assume the sign bit of the result
// will be 0 because that makes abs(INT_MIN) undefined.
if (match(RHS, m_Neg(m_Specific(LHS))) &&
Q.IIQ.hasNoSignedWrap(cast<Instruction>(RHS)))
MaxHighZeros = 1;
}
// Only known if known in both the LHS and RHS.
Known.One &= Known2.One;
Known.Zero &= Known2.Zero;
if (MaxHighOnes > 0)
Known.One.setHighBits(MaxHighOnes);
if (MaxHighZeros > 0)
Known.Zero.setHighBits(MaxHighZeros);
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:
// Fall through and handle them the same as zext/trunc.
LLVM_FALLTHROUGH;
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.
Type *ScalarTy = SrcTy->getScalarType();
SrcBitWidth = ScalarTy->isPointerTy() ?
Q.DL.getPointerTypeSizeInBits(ScalarTy) :
Q.DL.getTypeSizeInBits(ScalarTy);
assert(SrcBitWidth && "SrcBitWidth can't be zero");
Known = Known.anyextOrTrunc(SrcBitWidth);
computeKnownBits(I->getOperand(0), Known, Depth + 1, Q);
Known = Known.zextOrTrunc(BitWidth);
break;
}
case Instruction::BitCast: {
Type *SrcTy = I->getOperand(0)->getType();
if (SrcTy->isIntOrPtrTy() &&
// TODO: For now, not handling conversions like:
// (bitcast i64 %x to <2 x i32>)
!I->getType()->isVectorTy()) {
computeKnownBits(I->getOperand(0), Known, 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();
Known = Known.trunc(SrcBitWidth);
computeKnownBits(I->getOperand(0), Known, Depth + 1, Q);
// If the sign bit of the input is known set or clear, then we know the
// top bits of the result.
Known = Known.sext(BitWidth);
break;
}
case Instruction::Shl: {
// (shl X, C1) & C2 == 0 iff (X & C2 >>u C1) == 0
bool NSW = Q.IIQ.hasNoSignedWrap(cast<OverflowingBinaryOperator>(I));
auto KZF = [NSW](const APInt &KnownZero, unsigned ShiftAmt) {
APInt KZResult = KnownZero << ShiftAmt;
KZResult.setLowBits(ShiftAmt); // Low bits known 0.
// If this shift has "nsw" keyword, then the result is either a poison
// value or has the same sign bit as the first operand.
if (NSW && KnownZero.isSignBitSet())
KZResult.setSignBit();
return KZResult;
};
auto KOF = [NSW](const APInt &KnownOne, unsigned ShiftAmt) {
APInt KOResult = KnownOne << ShiftAmt;
if (NSW && KnownOne.isSignBitSet())
KOResult.setSignBit();
return KOResult;
};
computeKnownBitsFromShiftOperator(I, DemandedElts, Known, Known2, Depth, Q,
KZF, KOF);
break;
}
case Instruction::LShr: {
// (lshr X, C1) & C2 == 0 iff (-1 >> C1) & C2 == 0
auto KZF = [](const APInt &KnownZero, unsigned ShiftAmt) {
APInt KZResult = KnownZero.lshr(ShiftAmt);
// High bits known zero.
KZResult.setHighBits(ShiftAmt);
return KZResult;
};
auto KOF = [](const APInt &KnownOne, unsigned ShiftAmt) {
return KnownOne.lshr(ShiftAmt);
};
computeKnownBitsFromShiftOperator(I, DemandedElts, Known, Known2, Depth, Q,
KZF, KOF);
break;
}
case Instruction::AShr: {
// (ashr X, C1) & C2 == 0 iff (-1 >> C1) & C2 == 0
auto KZF = [](const APInt &KnownZero, unsigned ShiftAmt) {
return KnownZero.ashr(ShiftAmt);
};
auto KOF = [](const APInt &KnownOne, unsigned ShiftAmt) {
return KnownOne.ashr(ShiftAmt);
};
computeKnownBitsFromShiftOperator(I, DemandedElts, Known, Known2, Depth, Q,
KZF, KOF);
break;
}
case Instruction::Sub: {
bool NSW = Q.IIQ.hasNoSignedWrap(cast<OverflowingBinaryOperator>(I));
computeKnownBitsAddSub(false, I->getOperand(0), I->getOperand(1), NSW,
DemandedElts, Known, Known2, Depth, Q);
break;
}
case Instruction::Add: {
bool NSW = Q.IIQ.hasNoSignedWrap(cast<OverflowingBinaryOperator>(I));
computeKnownBitsAddSub(true, I->getOperand(0), I->getOperand(1), NSW,
DemandedElts, Known, Known2, 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), Known2, Depth + 1, Q);
// The low bits of the first operand are unchanged by the srem.
Known.Zero = Known2.Zero & LowBits;
Known.One = Known2.One & LowBits;
// If the first operand is non-negative or has all low bits zero, then
// the upper bits are all zero.
if (Known2.isNonNegative() || LowBits.isSubsetOf(Known2.Zero))
Known.Zero |= ~LowBits;
// If the first operand is negative and not all low bits are zero, then
// the upper bits are all one.
if (Known2.isNegative() && LowBits.intersects(Known2.One))
Known.One |= ~LowBits;
assert((Known.Zero & Known.One) == 0 && "Bits known to be one AND zero?");
break;
}
}
// The sign bit is the LHS's sign bit, except when the result of the
// remainder is zero.
computeKnownBits(I->getOperand(0), Known2, Depth + 1, Q);
// If it's known zero, our sign bit is also zero.
if (Known2.isNonNegative())
Known.makeNonNegative();
break;
case Instruction::URem: {
if (ConstantInt *Rem = dyn_cast<ConstantInt>(I->getOperand(1))) {
const APInt &RA = Rem->getValue();
if (RA.isPowerOf2()) {
APInt LowBits = (RA - 1);
computeKnownBits(I->getOperand(0), Known, Depth + 1, Q);
Known.Zero |= ~LowBits;
Known.One &= 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), Known, Depth + 1, Q);
computeKnownBits(I->getOperand(1), Known2, Depth + 1, Q);
unsigned Leaders =
std::max(Known.countMinLeadingZeros(), Known2.countMinLeadingZeros());
Known.resetAll();
Known.Zero.setHighBits(Leaders);
break;
}
case Instruction::Alloca:
Known.Zero.setLowBits(Log2(cast<AllocaInst>(I)->getAlign()));
break;
case Instruction::GetElementPtr: {
// Analyze all of the subscripts of this getelementptr instruction
// to determine if we can prove known low zero bits.
KnownBits LocalKnown(BitWidth);
computeKnownBits(I->getOperand(0), LocalKnown, Depth + 1, Q);
unsigned TrailZ = LocalKnown.countMinTrailingZeros();
gep_type_iterator GTI = gep_type_begin(I);
for (unsigned i = 1, e = I->getNumOperands(); i != e; ++i, ++GTI) {
// TrailZ can only become smaller, short-circuit if we hit zero.
if (TrailZ == 0)
break;
Value *Index = I->getOperand(i);
if (StructType *STy = GTI.getStructTypeOrNull()) {
// Handle struct member offset arithmetic.
// 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 = Q.DL.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 = Q.DL.getTypeAllocSize(IndexedTy).getKnownMinSize();
LocalKnown.Zero = LocalKnown.One = APInt(GEPOpiBits, 0);
computeKnownBits(Index, LocalKnown, Depth + 1, Q);
TrailZ = std::min(TrailZ,
unsigned(countTrailingZeros(TypeSize) +
LocalKnown.countMinTrailingZeros()));
}
}
Known.Zero.setLowBits(TrailZ);
break;
}
case Instruction::PHI: {
const 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);
Instruction *RInst = P->getIncomingBlock(!i)->getTerminator();
Instruction *LInst = P->getIncomingBlock(i)->getTerminator();
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
continue; // Check for recurrence with L and R flipped.
// Change the context instruction to the "edge" that flows into the
// phi. This is important because that is where the value is actually
// "evaluated" even though it is used later somewhere else. (see also
// D69571).
Query RecQ = Q;
// Ok, we have a PHI of the form L op= R. Check for low
// zero bits.
RecQ.CxtI = RInst;
computeKnownBits(R, Known2, Depth + 1, RecQ);
// We need to take the minimum number of known bits
KnownBits Known3(BitWidth);
RecQ.CxtI = LInst;
computeKnownBits(L, Known3, Depth + 1, RecQ);
Known.Zero.setLowBits(std::min(Known2.countMinTrailingZeros(),
Known3.countMinTrailingZeros()));
auto *OverflowOp = dyn_cast<OverflowingBinaryOperator>(LU);
if (OverflowOp && Q.IIQ.hasNoSignedWrap(OverflowOp)) {
// If initial value of recurrence is nonnegative, and we are adding
// a nonnegative number with nsw, the result can only be nonnegative
// or poison value regardless of the number of times we execute the
// add in phi recurrence. If initial value is negative and we are
// adding a negative number with nsw, the result can only be
// negative or poison value. Similar arguments apply to sub and mul.
//
// (add non-negative, non-negative) --> non-negative
// (add negative, negative) --> negative
if (Opcode == Instruction::Add) {
if (Known2.isNonNegative() && Known3.isNonNegative())
Known.makeNonNegative();
else if (Known2.isNegative() && Known3.isNegative())
Known.makeNegative();
}
// (sub nsw non-negative, negative) --> non-negative
// (sub nsw negative, non-negative) --> negative
else if (Opcode == Instruction::Sub && LL == I) {
if (Known2.isNonNegative() && Known3.isNegative())
Known.makeNonNegative();
else if (Known2.isNegative() && Known3.isNonNegative())
Known.makeNegative();
}
// (mul nsw non-negative, non-negative) --> non-negative
else if (Opcode == Instruction::Mul && Known2.isNonNegative() &&
Known3.isNonNegative())
Known.makeNonNegative();
}
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 && !Known.Zero && !Known.One) {
// Skip if every incoming value references to ourself.
if (dyn_cast_or_null<UndefValue>(P->hasConstantValue()))
break;
Known.Zero.setAllBits();
Known.One.setAllBits();
for (unsigned u = 0, e = P->getNumIncomingValues(); u < e; ++u) {
Value *IncValue = P->getIncomingValue(u);
// Skip direct self references.
if (IncValue == P) continue;
// Change the context instruction to the "edge" that flows into the
// phi. This is important because that is where the value is actually
// "evaluated" even though it is used later somewhere else. (see also
// D69571).
Query RecQ = Q;
RecQ.CxtI = P->getIncomingBlock(u)->getTerminator();
Known2 = KnownBits(BitWidth);
// Recurse, but cap the recursion to one level, because we don't
// want to waste time spinning around in loops.
computeKnownBits(IncValue, Known2, MaxDepth - 1, RecQ);
Known.Zero &= Known2.Zero;
Known.One &= Known2.One;
// If all bits have been ruled out, there's no need to check
// more operands.
if (!Known.Zero && !Known.One)
break;
}
}
break;
}
case Instruction::Call:
case Instruction::Invoke:
// If range metadata is attached to this call, set known bits from that,
// and then intersect with known bits based on other properties of the
// function.
if (MDNode *MD =
Q.IIQ.getMetadata(cast<Instruction>(I), LLVMContext::MD_range))
computeKnownBitsFromRangeMetadata(*MD, Known);
if (const Value *RV = cast<CallBase>(I)->getReturnedArgOperand()) {
computeKnownBits(RV, Known2, Depth + 1, Q);
Known.Zero |= Known2.Zero;
Known.One |= Known2.One;
}
if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
switch (II->getIntrinsicID()) {
default: break;
case Intrinsic::bitreverse:
computeKnownBits(I->getOperand(0), DemandedElts, Known2, Depth + 1, Q);
Known.Zero |= Known2.Zero.reverseBits();
Known.One |= Known2.One.reverseBits();
break;
case Intrinsic::bswap:
computeKnownBits(I->getOperand(0), DemandedElts, Known2, Depth + 1, Q);
Known.Zero |= Known2.Zero.byteSwap();
Known.One |= Known2.One.byteSwap();
break;
case Intrinsic::ctlz: {
computeKnownBits(I->getOperand(0), Known2, Depth + 1, Q);
// If we have a known 1, its position is our upper bound.
unsigned PossibleLZ = Known2.One.countLeadingZeros();
// If this call is undefined for 0, the result will be less than 2^n.
if (II->getArgOperand(1) == ConstantInt::getTrue(II->getContext()))
PossibleLZ = std::min(PossibleLZ, BitWidth - 1);
unsigned LowBits = Log2_32(PossibleLZ)+1;
Known.Zero.setBitsFrom(LowBits);
break;
}
case Intrinsic::cttz: {
computeKnownBits(I->getOperand(0), Known2, Depth + 1, Q);
// If we have a known 1, its position is our upper bound.
unsigned PossibleTZ = Known2.One.countTrailingZeros();
// If this call is undefined for 0, the result will be less than 2^n.
if (II->getArgOperand(1) == ConstantInt::getTrue(II->getContext()))
PossibleTZ = std::min(PossibleTZ, BitWidth - 1);
unsigned LowBits = Log2_32(PossibleTZ)+1;
Known.Zero.setBitsFrom(LowBits);
break;
}
case Intrinsic::ctpop: {
computeKnownBits(I->getOperand(0), Known2, Depth + 1, Q);
// We can bound the space the count needs. Also, bits known to be zero
// can't contribute to the population.
unsigned BitsPossiblySet = Known2.countMaxPopulation();
unsigned LowBits = Log2_32(BitsPossiblySet)+1;
Known.Zero.setBitsFrom(LowBits);
// TODO: we could bound KnownOne using the lower bound on the number
// of bits which might be set provided by popcnt KnownOne2.
break;
}
case Intrinsic::fshr:
case Intrinsic::fshl: {
const APInt *SA;
if (!match(I->getOperand(2), m_APInt(SA)))
break;
// Normalize to funnel shift left.
uint64_t ShiftAmt = SA->urem(BitWidth);
if (II->getIntrinsicID() == Intrinsic::fshr)
ShiftAmt = BitWidth - ShiftAmt;
KnownBits Known3(BitWidth);
computeKnownBits(I->getOperand(0), Known2, Depth + 1, Q);
computeKnownBits(I->getOperand(1), Known3, Depth + 1, Q);
Known.Zero =
Known2.Zero.shl(ShiftAmt) | Known3.Zero.lshr(BitWidth - ShiftAmt);
Known.One =
Known2.One.shl(ShiftAmt) | Known3.One.lshr(BitWidth - ShiftAmt);
break;
}
case Intrinsic::uadd_sat:
case Intrinsic::usub_sat: {
bool IsAdd = II->getIntrinsicID() == Intrinsic::uadd_sat;
computeKnownBits(I->getOperand(0), Known, Depth + 1, Q);
computeKnownBits(I->getOperand(1), Known2, Depth + 1, Q);
// Add: Leading ones of either operand are preserved.
// Sub: Leading zeros of LHS and leading ones of RHS are preserved
// as leading zeros in the result.
unsigned LeadingKnown;
if (IsAdd)
LeadingKnown = std::max(Known.countMinLeadingOnes(),
Known2.countMinLeadingOnes());
else
LeadingKnown = std::max(Known.countMinLeadingZeros(),
Known2.countMinLeadingOnes());
Known = KnownBits::computeForAddSub(
IsAdd, /* NSW */ false, Known, Known2);
// We select between the operation result and all-ones/zero
// respectively, so we can preserve known ones/zeros.
if (IsAdd) {
Known.One.setHighBits(LeadingKnown);
Known.Zero.clearAllBits();
} else {
Known.Zero.setHighBits(LeadingKnown);
Known.One.clearAllBits();
}
break;
}
case Intrinsic::x86_sse42_crc32_64_64:
Known.Zero.setBitsFrom(32);
break;
}
}
break;
case Instruction::ShuffleVector: {
auto *Shuf = dyn_cast<ShuffleVectorInst>(I);
// FIXME: Do we need to handle ConstantExpr involving shufflevectors?
if (!Shuf) {
Known.resetAll();
return;
}
// For undef elements, we don't know anything about the common state of
// the shuffle result.
APInt DemandedLHS, DemandedRHS;
if (!getShuffleDemandedElts(Shuf, DemandedElts, DemandedLHS, DemandedRHS)) {
Known.resetAll();
return;
}
Known.One.setAllBits();
Known.Zero.setAllBits();
if (!!DemandedLHS) {
const Value *LHS = Shuf->getOperand(0);
computeKnownBits(LHS, DemandedLHS, Known, Depth + 1, Q);
// If we don't know any bits, early out.
if (Known.isUnknown())
break;
}
if (!!DemandedRHS) {
const Value *RHS = Shuf->getOperand(1);
computeKnownBits(RHS, DemandedRHS, Known2, Depth + 1, Q);
Known.One &= Known2.One;
Known.Zero &= Known2.Zero;
}
break;
}
case Instruction::InsertElement: {
const Value *Vec = I->getOperand(0);
const Value *Elt = I->getOperand(1);
auto *CIdx = dyn_cast<ConstantInt>(I->getOperand(2));
// Early out if the index is non-constant or out-of-range.
unsigned NumElts = DemandedElts.getBitWidth();
if (!CIdx || CIdx->getValue().uge(NumElts)) {
Known.resetAll();
return;
}
Known.One.setAllBits();
Known.Zero.setAllBits();
unsigned EltIdx = CIdx->getZExtValue();
// Do we demand the inserted element?
if (DemandedElts[EltIdx]) {
computeKnownBits(Elt, Known, Depth + 1, Q);
// If we don't know any bits, early out.
if (Known.isUnknown())
break;
}
// We don't need the base vector element that has been inserted.
APInt DemandedVecElts = DemandedElts;
DemandedVecElts.clearBit(EltIdx);
if (!!DemandedVecElts) {
computeKnownBits(Vec, DemandedVecElts, Known2, Depth + 1, Q);
Known.One &= Known2.One;
Known.Zero &= Known2.Zero;
}
break;
}
case Instruction::ExtractElement: {
// Look through extract element. If the index is non-constant or
// out-of-range demand all elements, otherwise just the extracted element.
const Value *Vec = I->getOperand(0);
const Value *Idx = I->getOperand(1);
auto *CIdx = dyn_cast<ConstantInt>(Idx);
if (isa<ScalableVectorType>(Vec->getType())) {
// FIXME: there's probably *something* we can do with scalable vectors
Known.resetAll();
break;
}
unsigned NumElts = cast<FixedVectorType>(Vec->getType())->getNumElements();
APInt DemandedVecElts = APInt::getAllOnesValue(NumElts);
if (CIdx && CIdx->getValue().ult(NumElts))
DemandedVecElts = APInt::getOneBitSet(NumElts, CIdx->getZExtValue());
computeKnownBits(Vec, DemandedVecElts, Known, Depth + 1, Q);
break;
}
case Instruction::ExtractValue:
if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I->getOperand(0))) {
const 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, DemandedElts,
Known, Known2, Depth, Q);
break;
case Intrinsic::usub_with_overflow:
case Intrinsic::ssub_with_overflow:
computeKnownBitsAddSub(false, II->getArgOperand(0),
II->getArgOperand(1), false, DemandedElts,
Known, Known2, Depth, Q);
break;
case Intrinsic::umul_with_overflow:
case Intrinsic::smul_with_overflow:
computeKnownBitsMul(II->getArgOperand(0), II->getArgOperand(1), false,
DemandedElts, Known, Known2, Depth, Q);
break;
}
}
}
break;
}
}
/// Determine which bits of V are known to be either zero or one and return
/// them.
KnownBits computeKnownBits(const Value *V, const APInt &DemandedElts,
unsigned Depth, const Query &Q) {
KnownBits Known(getBitWidth(V->getType(), Q.DL));
computeKnownBits(V, DemandedElts, Known, Depth, Q);
return Known;
}
/// Determine which bits of V are known to be either zero or one and return
/// them.
KnownBits computeKnownBits(const Value *V, unsigned Depth, const Query &Q) {
KnownBits Known(getBitWidth(V->getType(), Q.DL));
computeKnownBits(V, Known, Depth, Q);
return Known;
}
/// Determine which bits of V are known to be either zero or one and return
/// them in the Known bit set.
///
/// NOTE: we cannot consider 'undef' to be "IsZero" here. The problem is that
/// 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, 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 demanded elements in the vector specified by DemandedElts.
void computeKnownBits(const Value *V, const APInt &DemandedElts,
KnownBits &Known, unsigned Depth, const Query &Q) {
if (!DemandedElts || isa<ScalableVectorType>(V->getType())) {
// No demanded elts or V is a scalable vector, better to assume we don't
// know anything.
Known.resetAll();
return;
}
assert(V && "No Value?");
assert(Depth <= MaxDepth && "Limit Search Depth");
#ifndef NDEBUG
Type *Ty = V->getType();
unsigned BitWidth = Known.getBitWidth();
assert((Ty->isIntOrIntVectorTy(BitWidth) || Ty->isPtrOrPtrVectorTy()) &&
"Not integer or pointer type!");
if (auto *FVTy = dyn_cast<FixedVectorType>(Ty)) {
assert(
FVTy->getNumElements() == DemandedElts.getBitWidth() &&
"DemandedElt width should equal the fixed vector number of elements");
} else {
assert(DemandedElts == APInt(1, 1) &&
"DemandedElt width should be 1 for scalars");
}
Type *ScalarTy = Ty->getScalarType();
if (ScalarTy->isPointerTy()) {
assert(BitWidth == Q.DL.getPointerTypeSizeInBits(ScalarTy) &&
"V and Known should have same BitWidth");
} else {
assert(BitWidth == Q.DL.getTypeSizeInBits(ScalarTy) &&
"V and Known should have same BitWidth");
}
#endif
const APInt *C;
if (match(V, m_APInt(C))) {
// We know all of the bits for a scalar constant or a splat vector constant!
Known.One = *C;
Known.Zero = ~Known.One;
return;
}
// Null and aggregate-zero are all-zeros.
if (isa<ConstantPointerNull>(V) || isa<ConstantAggregateZero>(V)) {
Known.setAllZero();
return;
}
// Handle a constant vector by taking the intersection of the known bits of
// each element.
if (const ConstantDataVector *CDV = dyn_cast<ConstantDataVector>(V)) {
// We know that CDV must be a vector of integers. Take the intersection of
// each element.
Known.Zero.setAllBits(); Known.One.setAllBits();
for (unsigned i = 0, e = CDV->getNumElements(); i != e; ++i) {
if (!DemandedElts[i])
continue;
APInt Elt = CDV->getElementAsAPInt(i);
Known.Zero &= ~Elt;
Known.One &= Elt;
}
return;
}
if (const auto *CV = dyn_cast<ConstantVector>(V)) {
// We know that CV must be a vector of integers. Take the intersection of
// each element.
Known.Zero.setAllBits(); Known.One.setAllBits();
for (unsigned i = 0, e = CV->getNumOperands(); i != e; ++i) {
if (!DemandedElts[i])
continue;
Constant *Element = CV->getAggregateElement(i);
auto *ElementCI = dyn_cast_or_null<ConstantInt>(Element);
if (!ElementCI) {
Known.resetAll();
return;
}
const APInt &Elt = ElementCI->getValue();
Known.Zero &= ~Elt;
Known.One &= Elt;
}
return;
}
// Start out not knowing anything.
Known.resetAll();
// We can't imply anything about undefs.
if (isa<UndefValue>(V))
return;
// There's no point in looking through other users of ConstantData for
// assumptions. Confirm that we've handled them all.
assert(!isa<ConstantData>(V) && "Unhandled constant data!");
// 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 (const GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) {
if (!GA->isInterposable())
computeKnownBits(GA->getAliasee(), Known, Depth + 1, Q);
return;
}
if (const Operator *I = dyn_cast<Operator>(V))
computeKnownBitsFromOperator(I, DemandedElts, Known, Depth, Q);
// Aligned pointers have trailing zeros - refine Known.Zero set
if (isa<PointerType>(V->getType())) {
Align Alignment = V->getPointerAlignment(Q.DL);
Known.Zero.setLowBits(countTrailingZeros(Alignment.value()));
}
// computeKnownBitsFromAssume strictly refines Known.
// Therefore, we run them after computeKnownBitsFromOperator.
// Check whether a nearby assume intrinsic can determine some known bits.
computeKnownBitsFromAssume(V, Known, Depth, Q);
assert((Known.Zero & Known.One) == 0 && "Bits known to be one AND zero?");
}
/// 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(const Value *V, bool OrZero, unsigned Depth,
const Query &Q) {
assert(Depth <= MaxDepth && "Limit Search Depth");
// Attempt to match against constants.
if (OrZero && match(V, m_Power2OrZero()))
return true;
if (match(V, m_Power2()))
return true;
// 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;
// (signmask) >>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_SignMask(), 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 left or a logical shift right 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_LShr(m_Value(X), m_Value()))))
return isKnownToBeAPowerOfTwo(X, /*OrZero*/ true, Depth, Q);
if (const ZExtInst *ZI = dyn_cast<ZExtInst>(V))
return isKnownToBeAPowerOfTwo(ZI->getOperand(0), OrZero, Depth, Q);
if (const 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)))) {
const OverflowingBinaryOperator *VOBO = cast<OverflowingBinaryOperator>(V);
if (OrZero || Q.IIQ.hasNoUnsignedWrap(VOBO) ||
Q.IIQ.hasNoSignedWrap(VOBO)) {
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();
KnownBits LHSBits(BitWidth);
computeKnownBits(X, LHSBits, Depth, Q);
KnownBits RHSBits(BitWidth);
computeKnownBits(Y, RHSBits, 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 ((~(LHSBits.Zero & RHSBits.Zero)).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 || RHSBits.One.getBoolValue() || LHSBits.One.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;
}
/// 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(const GEPOperator *GEP, unsigned Depth,
const Query &Q) {
const Function *F = nullptr;
if (const Instruction *I = dyn_cast<Instruction>(GEP))
F = I->getFunction();
if (!GEP->isInBounds() ||
NullPointerIsDefined(F, GEP->getPointerAddressSpace()))
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(), Depth, Q))
return true;
// 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 = GTI.getStructTypeOrNull()) {
ConstantInt *OpC = cast<ConstantInt>(GTI.getOperand());
unsigned ElementIdx = OpC->getZExtValue();
const StructLayout *SL = Q.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 (Q.DL.getTypeAllocSize(GTI.getIndexedType()).getKnownMinSize() == 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(), Depth, Q))
return true;
}
return false;
}
static bool isKnownNonNullFromDominatingCondition(const Value *V,
const Instruction *CtxI,
const DominatorTree *DT) {
if (isa<Constant>(V))
return false;
if (!CtxI || !DT)
return false;
unsigned NumUsesExplored = 0;
for (auto *U : V->users()) {
// Avoid massive lists
if (NumUsesExplored >= DomConditionsMaxUses)
break;
NumUsesExplored++;
// If the value is used as an argument to a call or invoke, then argument
// attributes may provide an answer about null-ness.
if (const auto *CB = dyn_cast<CallBase>(U))
if (auto *CalledFunc = CB->getCalledFunction())
for (const Argument &Arg : CalledFunc->args())
if (CB->getArgOperand(Arg.getArgNo()) == V &&
Arg.hasNonNullAttr() && DT->dominates(CB, CtxI))
return true;
// If the value is used as a load/store, then the pointer must be non null.
if (V == getLoadStorePointerOperand(U)) {
const Instruction *I = cast<Instruction>(U);
if (!NullPointerIsDefined(I->getFunction(),
V->getType()->getPointerAddressSpace()) &&
DT->dominates(I, CtxI))
return true;
}
// Consider only compare instructions uniquely controlling a branch
CmpInst::Predicate Pred;
if (!match(const_cast<User *>(U),
m_c_ICmp(Pred, m_Specific(V), m_Zero())) ||
(Pred != ICmpInst::ICMP_EQ && Pred != ICmpInst::ICMP_NE))
continue;
SmallVector<const User *, 4> WorkList;
SmallPtrSet<const User *, 4> Visited;
for (auto *CmpU : U->users()) {
assert(WorkList.empty() && "Should be!");
if (Visited.insert(CmpU).second)
WorkList.push_back(CmpU);
while (!WorkList.empty()) {
auto *Curr = WorkList.pop_back_val();
// If a user is an AND, add all its users to the work list. We only
// propagate "pred != null" condition through AND because it is only
// correct to assume that all conditions of AND are met in true branch.
// TODO: Support similar logic of OR and EQ predicate?
if (Pred == ICmpInst::ICMP_NE)
if (auto *BO = dyn_cast<BinaryOperator>(Curr))
if (BO->getOpcode() == Instruction::And) {
for (auto *BOU : BO->users())
if (Visited.insert(BOU).second)
WorkList.push_back(BOU);
continue;
}
if (const BranchInst *BI = dyn_cast<BranchInst>(Curr)) {
assert(BI->isConditional() && "uses a comparison!");
BasicBlock *NonNullSuccessor =
BI->getSuccessor(Pred == ICmpInst::ICMP_EQ ? 1 : 0);
BasicBlockEdge Edge(BI->getParent(), NonNullSuccessor);
if (Edge.isSingleEdge() && DT->dominates(Edge, CtxI->getParent()))
return true;
} else if (Pred == ICmpInst::ICMP_NE && isGuard(Curr) &&
DT->dominates(cast<Instruction>(Curr), CtxI)) {
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(const 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 demanded element is known to be non-zero when
/// defined. For pointers, if the context instruction and dominator tree are
/// specified, perform context-sensitive analysis and return true if the
/// pointer couldn't possibly be null at the specified instruction.
/// Supports values with integer or pointer type and vectors of integers.
bool isKnownNonZero(const Value *V, const APInt &DemandedElts, unsigned Depth,
const Query &Q) {
// FIXME: We currently have no way to represent the DemandedElts of a scalable
// vector
if (isa<ScalableVectorType>(V->getType()))
return false;
if (auto *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;
if (auto *CE = dyn_cast<ConstantExpr>(C)) {
// See the comment for IntToPtr/PtrToInt instructions below.
if (CE->getOpcode() == Instruction::IntToPtr ||
CE->getOpcode() == Instruction::PtrToInt)
if (Q.DL.getTypeSizeInBits(CE->getOperand(0)->getType()) <=
Q.DL.getTypeSizeInBits(CE->getType()))
return isKnownNonZero(CE->getOperand(0), Depth, Q);
}
// For constant vectors, check that all elements are undefined or known
// non-zero to determine that the whole vector is known non-zero.
if (auto *VecTy = dyn_cast<FixedVectorType>(C->getType())) {
for (unsigned i = 0, e = VecTy->getNumElements(); i != e; ++i) {
if (!DemandedElts[i])
continue;
Constant *Elt = C->getAggregateElement(i);
if (!Elt || Elt->isNullValue())
return false;
if (!isa<UndefValue>(Elt) && !isa<ConstantInt>(Elt))
return false;
}
return true;
}
// A global variable in address space 0 is non null unless extern weak
// or an absolute symbol reference. Other address spaces may have null as a
// valid address for a global, so we can't assume anything.
if (const GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
if (!GV->isAbsoluteSymbolRef() && !GV->hasExternalWeakLinkage() &&
GV->getType()->getAddressSpace() == 0)
return true;
} else
return false;
}
if (auto *I = dyn_cast<Instruction>(V)) {
if (MDNode *Ranges = Q.IIQ.getMetadata(I, LLVMContext::MD_range)) {
// If the possible ranges don't contain zero, then the value is
// definitely non-zero.
if (auto *Ty = dyn_cast<IntegerType>(V->getType())) {
const APInt ZeroValue(Ty->getBitWidth(), 0);
if (rangeMetadataExcludesValue(Ranges, ZeroValue))
return true;
}
}
}
if (isKnownNonZeroFromAssume(V, Q))
return true;
// Some of the tests below are recursive, so bail out if we hit the limit.
if (Depth++ >= MaxDepth)
return false;
// Check for pointer simplifications.
if (PointerType *PtrTy = dyn_cast<PointerType>(V->getType())) {
// Alloca never returns null, malloc might.
if (isa<AllocaInst>(V) && Q.DL.getAllocaAddrSpace() == 0)
return true;
// A byval, inalloca may not be null in a non-default addres space. A
// nonnull argument is assumed never 0.
if (const Argument *A = dyn_cast<Argument>(V)) {
if (((A->hasPassPointeeByValueCopyAttr() &&
!NullPointerIsDefined(A->getParent(), PtrTy->getAddressSpace())) ||
A->hasNonNullAttr()))
return true;
}
// A Load tagged with nonnull metadata is never null.
if (const LoadInst *LI = dyn_cast<LoadInst>(V))
if (Q.IIQ.getMetadata(LI, LLVMContext::MD_nonnull))
return true;
if (const auto *Call = dyn_cast<CallBase>(V)) {
if (Call->isReturnNonNull())
return true;
if (const auto *RP = getArgumentAliasingToReturnedPointer(Call, true))
return isKnownNonZero(RP, Depth, Q);
}
}
if (isKnownNonNullFromDominatingCondition(V, Q.CxtI, Q.DT))
return true;
// Check for recursive pointer simplifications.
if (V->getType()->isPointerTy()) {
// Look through bitcast operations, GEPs, and int2ptr instructions as they
// do not alter the value, or at least not the nullness property of the
// value, e.g., int2ptr is allowed to zero/sign extend the value.
//
// Note that we have to take special care to avoid looking through
// truncating casts, e.g., int2ptr/ptr2int with appropriate sizes, as well
// as casts that can alter the value, e.g., AddrSpaceCasts.
if (const GEPOperator *GEP = dyn_cast<GEPOperator>(V))
if (isGEPKnownNonNull(GEP, Depth, Q))
return true;
if (auto *BCO = dyn_cast<BitCastOperator>(V))
return isKnownNonZero(BCO->getOperand(0), Depth, Q);
if (auto *I2P = dyn_cast<IntToPtrInst>(V))
if (Q.DL.getTypeSizeInBits(I2P->getSrcTy()) <=
Q.DL.getTypeSizeInBits(I2P->getDestTy()))
return isKnownNonZero(I2P->getOperand(0), Depth, Q);
}
// Similar to int2ptr above, we can look through ptr2int here if the cast
// is a no-op or an extend and not a truncate.
if (auto *P2I = dyn_cast<PtrToIntInst>(V))
if (Q.DL.getTypeSizeInBits(P2I->getSrcTy()) <=
Q.DL.getTypeSizeInBits(P2I->getDestTy()))
return isKnownNonZero(P2I->getOperand(0), Depth, Q);
unsigned BitWidth = getBitWidth(V->getType()->getScalarType(), Q.DL);
// 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, DemandedElts, Depth, Q) ||
isKnownNonZero(Y, DemandedElts, Depth, Q);
// ext X != 0 if X != 0.
if (isa<SExtInst>(V) || isa<ZExtInst>(V))
return isKnownNonZero(cast<Instruction>(V)->getOperand(0), 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 (match(V, m_Shl(m_Value(X), m_Value(Y)))) {
// shl nuw can't remove any non-zero bits.
const OverflowingBinaryOperator *BO = cast<OverflowingBinaryOperator>(V);
if (Q.IIQ.hasNoUnsignedWrap(BO))
return isKnownNonZero(X, Depth, Q);
KnownBits Known(BitWidth);
computeKnownBits(X, DemandedElts, Known, Depth, Q);
if (Known.One[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.
const PossiblyExactOperator *BO = cast<PossiblyExactOperator>(V);
if (BO->isExact())
return isKnownNonZero(X, Depth, Q);
KnownBits Known = computeKnownBits(X, DemandedElts, Depth, Q);
if (Known.isNegative())
return true;
// If the shifter operand is a constant, and all of the bits shifted
// out are known to be zero, and X is known non-zero then at least one
// non-zero bit must remain.
if (ConstantInt *Shift = dyn_cast<ConstantInt>(Y)) {
auto ShiftVal = Shift->getLimitedValue(BitWidth - 1);
// Is there a known one in the portion not shifted out?
if (Known.countMaxLeadingZeros() < BitWidth - ShiftVal)
return true;
// Are all the bits to be shifted out known zero?
if (Known.countMinTrailingZeros() >= ShiftVal)
return isKnownNonZero(X, DemandedElts, Depth, Q);
}
}
// 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, DemandedElts, Depth, Q);
}
// X + Y.
else if (match(V, m_Add(m_Value(X), m_Value(Y)))) {
KnownBits XKnown = computeKnownBits(X, DemandedElts, Depth, Q);
KnownBits YKnown = computeKnownBits(Y, DemandedElts, 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 (XKnown.isNonNegative() && YKnown.isNonNegative())
if (isKnownNonZero(X, DemandedElts, Depth, Q) ||
isKnownNonZero(Y, DemandedElts, 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 (XKnown.isNegative() && YKnown.isNegative()) {
APInt Mask = APInt::getSignedMaxValue(BitWidth);
// The sign bit of X is set. If some other bit is set then X is not equal
// to INT_MIN.
if (XKnown.One.intersects(Mask))
return true;
// The sign bit of Y is set. If some other bit is set then Y is not equal
// to INT_MIN.
if (YKnown.One.intersects(Mask))
return true;
}
// The sum of a non-negative number and a power of two is not zero.
if (XKnown.isNonNegative() &&
isKnownToBeAPowerOfTwo(Y, /*OrZero*/ false, Depth, Q))
return true;
if (YKnown.isNonNegative() &&
isKnownToBeAPowerOfTwo(X, /*OrZero*/ false, Depth, Q))
return true;
}
// X * Y.
else if (match(V, m_Mul(m_Value(X), m_Value(Y)))) {
const 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 ((Q.IIQ.hasNoSignedWrap(BO) || Q.IIQ.hasNoUnsignedWrap(BO)) &&
isKnownNonZero(X, DemandedElts, Depth, Q) &&
isKnownNonZero(Y, DemandedElts, Depth, Q))
return true;
}
// (C ? X : Y) != 0 if X != 0 and Y != 0.
else if (const SelectInst *SI = dyn_cast<SelectInst>(V)) {
if (isKnownNonZero(SI->getTrueValue(), DemandedElts, Depth, Q) &&
isKnownNonZero(SI->getFalseValue(), DemandedElts, Depth, Q))
return true;
}
// PHI
else if (const PHINode *PN = dyn_cast<PHINode>(V)) {
// Try and detect a recurrence that monotonically increases from a
// starting value, as these are common as induction variables.
if (PN->getNumIncomingValues() == 2) {
Value *Start = PN->getIncomingValue(0);
Value *Induction = PN->getIncomingValue(1);
if (isa<ConstantInt>(Induction) && !isa<ConstantInt>(Start))
std::swap(Start, Induction);
if (ConstantInt *C = dyn_cast<ConstantInt>(Start)) {
if (!C->isZero() && !C->isNegative()) {
ConstantInt *X;
if (Q.IIQ.UseInstrInfo &&
(match(Induction, m_NSWAdd(m_Specific(PN), m_ConstantInt(X))) ||
match(Induction, m_NUWAdd(m_Specific(PN), m_ConstantInt(X)))) &&
!X->isNegative())
return true;
}
}
}
// Check if all incoming values are non-zero constant.
bool AllNonZeroConstants = llvm::all_of(PN->operands(), [](Value *V) {
return isa<ConstantInt>(V) && !cast<ConstantInt>(V)->isZero();
});
if (AllNonZeroConstants)
return true;
}
// ExtractElement
else if (const auto *EEI = dyn_cast<ExtractElementInst>(V)) {
const Value *Vec = EEI->getVectorOperand();
const Value *Idx = EEI->getIndexOperand();
auto *CIdx = dyn_cast<ConstantInt>(Idx);
unsigned NumElts = cast<FixedVectorType>(Vec->getType())->getNumElements();
APInt DemandedVecElts = APInt::getAllOnesValue(NumElts);
if (CIdx && CIdx->getValue().ult(NumElts))
DemandedVecElts = APInt::getOneBitSet(NumElts, CIdx->getZExtValue());
return isKnownNonZero(Vec, DemandedVecElts, Depth, Q);
}
KnownBits Known(BitWidth);
computeKnownBits(V, DemandedElts, Known, Depth, Q);
return Known.One != 0;
}
bool isKnownNonZero(const Value* V, unsigned Depth, const Query& Q) {
// FIXME: We currently have no way to represent the DemandedElts of a scalable
// vector
if (isa<ScalableVectorType>(V->getType()))
return false;
auto *FVTy = dyn_cast<FixedVectorType>(V->getType());
APInt DemandedElts =
FVTy ? APInt::getAllOnesValue(FVTy->getNumElements()) : APInt(1, 1);
return isKnownNonZero(V, DemandedElts, Depth, Q);
}
/// Return true if V2 == V1 + X, where X is known non-zero.
static bool isAddOfNonZero(const Value *V1, const Value *V2, const Query &Q) {
const BinaryOperator *BO = dyn_cast<BinaryOperator>(V1);
if (!BO || BO->getOpcode() != Instruction::Add)
return false;
Value *Op = nullptr;
if (V2 == BO->getOperand(0))
Op = BO->getOperand(1);
else if (V2 == BO->getOperand(1))
Op = BO->getOperand(0);
else
return false;
return isKnownNonZero(Op, 0, Q);
}
/// Return true if it is known that V1 != V2.
static bool isKnownNonEqual(const Value *V1, const Value *V2, const Query &Q) {
if (V1 == V2)
return false;
if (V1->getType() != V2->getType())
// We can't look through casts yet.
return false;
if (isAddOfNonZero(V1, V2, Q) || isAddOfNonZero(V2, V1, Q))
return true;
if (V1->getType()->isIntOrIntVectorTy()) {
// Are any known bits in V1 contradictory to known bits in V2? If V1
// has a known zero where V2 has a known one, they must not be equal.
KnownBits Known1 = computeKnownBits(V1, 0, Q);
KnownBits Known2 = computeKnownBits(V2, 0, Q);
if (Known1.Zero.intersects(Known2.One) ||
Known2.Zero.intersects(Known1.One))
return true;
}
return false;
}
/// 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, 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(const Value *V, const APInt &Mask, unsigned Depth,
const Query &Q) {
KnownBits Known(Mask.getBitWidth());
computeKnownBits(V, Known, Depth, Q);
return Mask.isSubsetOf(Known.Zero);
}
// Match a signed min+max clamp pattern like smax(smin(In, CHigh), CLow).
// Returns the input and lower/upper bounds.
static bool isSignedMinMaxClamp(const Value *Select, const Value *&In,
const APInt *&CLow, const APInt *&CHigh) {
assert(isa<Operator>(Select) &&
cast<Operator>(Select)->getOpcode() == Instruction::Select &&
"Input should be a Select!");
const Value *LHS = nullptr, *RHS = nullptr;
SelectPatternFlavor SPF = matchSelectPattern(Select, LHS, RHS).Flavor;
if (SPF != SPF_SMAX && SPF != SPF_SMIN)
return false;
if (!match(RHS, m_APInt(CLow)))
return false;
const Value *LHS2 = nullptr, *RHS2 = nullptr;
SelectPatternFlavor SPF2 = matchSelectPattern(LHS, LHS2, RHS2).Flavor;
if (getInverseMinMaxFlavor(SPF) != SPF2)
return false;
if (!match(RHS2, m_APInt(CHigh)))
return false;
if (SPF == SPF_SMIN)
std::swap(CLow, CHigh);
In = LHS2;
return CLow->sle(*CHigh);
}
/// For vector constants, loop over the elements and find the constant with the
/// minimum number of sign bits. Return 0 if the value is not a vector constant
/// or if any element was not analyzed; otherwise, return the count for the
/// element with the minimum number of sign bits.
static unsigned computeNumSignBitsVectorConstant(const Value *V,
const APInt &DemandedElts,
unsigned TyBits) {
const auto *CV = dyn_cast<Constant>(V);
if (!CV || !isa<FixedVectorType>(CV->getType()))
return 0;
unsigned MinSignBits = TyBits;
unsigned NumElts = cast<FixedVectorType>(CV->getType())->getNumElements();
for (unsigned i = 0; i != NumElts; ++i) {
if (!DemandedElts[i])
continue;
// If we find a non-ConstantInt, bail out.
auto *Elt = dyn_cast_or_null<ConstantInt>(CV->getAggregateElement(i));
if (!Elt)
return 0;
MinSignBits = std::min(MinSignBits, Elt->getValue().getNumSignBits());
}
return MinSignBits;
}
static unsigned ComputeNumSignBitsImpl(const Value *V,
const APInt &DemandedElts,
unsigned Depth, const Query &Q);
static unsigned ComputeNumSignBits(const Value *V, const APInt &DemandedElts,
unsigned Depth, const Query &Q) {
unsigned Result = ComputeNumSignBitsImpl(V, DemandedElts, Depth, Q);
assert(Result > 0 && "At least one sign bit needs to be present!");
return Result;
}
/// 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. For vectors, return the number of sign bits for the
/// vector element with the minimum number of known sign bits of the demanded
/// elements in the vector specified by DemandedElts.
static unsigned ComputeNumSignBitsImpl(const Value *V,
const APInt &DemandedElts,
unsigned Depth, const Query &Q) {
Type *Ty = V->getType();
// FIXME: We currently have no way to represent the DemandedElts of a scalable
// vector
if (isa<ScalableVectorType>(Ty))
return 1;
#ifndef NDEBUG
assert(Depth <= MaxDepth && "Limit Search Depth");
if (auto *FVTy = dyn_cast<FixedVectorType>(Ty)) {
assert(
FVTy->getNumElements() == DemandedElts.getBitWidth() &&
"DemandedElt width should equal the fixed vector number of elements");
} else {
assert(DemandedElts == APInt(1, 1) &&
"DemandedElt width should be 1 for scalars");
}
#endif
// We return the minimum number of sign bits that are guaranteed to be present
// in V, so for undef we have to conservatively return 1. We don't have the
// same behavior for poison though -- that's a FIXME today.
Type *ScalarTy = Ty->getScalarType();
unsigned TyBits = ScalarTy->isPointerTy() ?
Q.DL.getPointerTypeSizeInBits(ScalarTy) :
Q.DL.getTypeSizeInBits(ScalarTy);
unsigned Tmp, Tmp2;
unsigned FirstAnswer = 1;
// Note that ConstantInt is handled by the general computeKnownBits case
// below.
if (Depth == MaxDepth)
return 1; // Limit search depth.
if (auto *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), Depth + 1, Q) + Tmp;
case Instruction::SDiv: {
const APInt *Denominator;
// sdiv X, C -> adds log(C) sign bits.
if (match(U->getOperand(1), m_APInt(Denominator))) {
// Ignore non-positive denominator.
if (!Denominator->isStrictlyPositive())
break;
// Calculate the incoming numerator bits.
unsigned NumBits = ComputeNumSignBits(U->getOperand(0), Depth + 1, Q);
// Add floor(log(C)) bits to the numerator bits.
return std::min(TyBits, NumBits + Denominator->logBase2());
}
break;
}
case Instruction::SRem: {
const APInt *Denominator;
// srem X, C -> we know that the result is within [-C+1,C) when C is a
// positive constant. This let us put a lower bound on the number of sign
// bits.
if (match(U->getOperand(1), m_APInt(Denominator))) {
// Ignore non-positive denominator.
if (!Denominator->isStrictlyPositive())
break;
// Calculate the incoming numerator bits. SRem by a positive constant
// can't lower the number of sign bits.
unsigned NumrBits = ComputeNumSignBits(U->getOperand(0), Depth + 1, Q);
// Calculate the leading sign bit constraints by examining the
// denominator. Given that the denominator is positive, there are two
// cases:
//
// 1. the numerator is positive. The result range is [0,C) and [0,C) u<
// (1 << ceilLogBase2(C)).
//
// 2. the numerator is negative. Then the result range is (-C,0] and
// integers in (-C,0] are either 0 or >u (-1 << ceilLogBase2(C)).
//
// Thus a lower bound on the number of sign bits is `TyBits -
// ceilLogBase2(C)`.
unsigned ResBits = TyBits - Denominator->ceilLogBase2();
return std::max(NumrBits, ResBits);
}
break;
}
case Instruction::AShr: {
Tmp = ComputeNumSignBits(U->getOperand(0), Depth + 1, Q);
// ashr X, C -> adds C sign bits. Vectors too.
const APInt *ShAmt;
if (match(U->getOperand(1), m_APInt(ShAmt))) {
if (ShAmt->uge(TyBits))
break; // Bad shift.
unsigned ShAmtLimited = ShAmt->getZExtValue();
Tmp += ShAmtLimited;
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), Depth + 1, Q);
if (ShAmt->uge(TyBits) || // Bad shift.
ShAmt->uge(Tmp)) break; // Shifted all sign bits out.
Tmp2 = ShAmt->getZExtValue();
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), Depth + 1, Q);
if (Tmp != 1) {
Tmp2 = ComputeNumSignBits(U->getOperand(1), 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: {
// If we have a clamp pattern, we know that the number of sign bits will
// be the minimum of the clamp min/max range.
const Value *X;
const APInt *CLow, *CHigh;
if (isSignedMinMaxClamp(U, X, CLow, CHigh))
return std::min(CLow->getNumSignBits(), CHigh->getNumSignBits());
Tmp = ComputeNumSignBits(U->getOperand(1), Depth + 1, Q);
if (Tmp == 1) break;
Tmp2 = ComputeNumSignBits(U->getOperand(2), 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), Depth + 1, Q);
if (Tmp == 1) break;
// Special case decrementing a value (ADD X, -1):
if (const auto *CRHS = dyn_cast<Constant>(U->getOperand(1)))
if (CRHS->isAllOnesValue()) {
KnownBits Known(TyBits);
computeKnownBits(U->getOperand(0), Known, 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 ((Known.Zero | 1).isAllOnesValue())
return TyBits;
// If we are subtracting one from a positive number, there is no carry
// out of the result.
if (Known.isNonNegative())
return Tmp;
}
Tmp2 = ComputeNumSignBits(U->getOperand(1), Depth + 1, Q);
if (Tmp2 == 1) break;
return std::min(Tmp, Tmp2) - 1;
case Instruction::Sub:
Tmp2 = ComputeNumSignBits(U->getOperand(1), Depth + 1, Q);
if (Tmp2 == 1) break;
// Handle NEG.
if (const auto *CLHS = dyn_cast<Constant>(U->getOperand(0)))
if (CLHS->isNullValue()) {
KnownBits Known(TyBits);
computeKnownBits(U->getOperand(1), Known, 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 ((Known.Zero | 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 (Known.isNonNegative())
return Tmp2;