//===- llvm/Analysis/ValueTracking.h - Walk computations --------*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file contains routines that help analyze properties that chains of
// computations have.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_ANALYSIS_VALUETRACKING_H
#define LLVM_ANALYSIS_VALUETRACKING_H
#include "llvm/IR/CallSite.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/Support/DataTypes.h"
namespace llvm {
template <typename T> class ArrayRef;
class APInt;
class AddOperator;
class AssumptionCache;
class DataLayout;
class DominatorTree;
class GEPOperator;
class Instruction;
struct KnownBits;
class Loop;
class LoopInfo;
class OptimizationRemarkEmitter;
class MDNode;
class StringRef;
class TargetLibraryInfo;
class Value;
namespace Intrinsic {
enum ID : unsigned;
}
/// Determine which bits of V are known to be either zero or one and return
/// them in the KnownZero/KnownOne bit sets.
///
/// 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 known zero and known one values are the
/// same width as the vector element, and the bit is set only if it is true
/// for all of the elements in the vector.
void computeKnownBits(const Value *V, KnownBits &Known,
const DataLayout &DL, unsigned Depth = 0,
AssumptionCache *AC = nullptr,
const Instruction *CxtI = nullptr,
const DominatorTree *DT = nullptr,
OptimizationRemarkEmitter *ORE = nullptr);
/// Returns the known bits rather than passing by reference.
KnownBits computeKnownBits(const Value *V, const DataLayout &DL,
unsigned Depth = 0, AssumptionCache *AC = nullptr,
const Instruction *CxtI = nullptr,
const DominatorTree *DT = nullptr,
OptimizationRemarkEmitter *ORE = nullptr);
/// Compute known bits from the range metadata.
/// \p KnownZero the set of bits that are known to be zero
/// \p KnownOne the set of bits that are known to be one
void computeKnownBitsFromRangeMetadata(const MDNode &Ranges,
KnownBits &Known);
/// Return true if LHS and RHS have no common bits set.
bool haveNoCommonBitsSet(const Value *LHS, const Value *RHS,
const DataLayout &DL,
AssumptionCache *AC = nullptr,
const Instruction *CxtI = nullptr,
const DominatorTree *DT = nullptr);
/// 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 type and
/// vectors of integers. If 'OrZero' is set, then return true if the given
/// value is either a power of two or zero.
bool isKnownToBeAPowerOfTwo(const Value *V, const DataLayout &DL,
bool OrZero = false, unsigned Depth = 0,
AssumptionCache *AC = nullptr,
const Instruction *CxtI = nullptr,
const DominatorTree *DT = nullptr);
bool isOnlyUsedInZeroEqualityComparison(const Instruction *CxtI);
/// Return true if the given value is known to be non-zero when defined. For
/// vectors, return true if every element is known to be non-zero when
/// defined. 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 DataLayout &DL, unsigned Depth = 0,
AssumptionCache *AC = nullptr,
const Instruction *CxtI = nullptr,
const DominatorTree *DT = nullptr);
/// Returns true if the give value is known to be non-negative.
bool isKnownNonNegative(const Value *V, const DataLayout &DL,
unsigned Depth = 0,
AssumptionCache *AC = nullptr,
const Instruction *CxtI = nullptr,
const DominatorTree *DT = nullptr);
/// Returns true if the given value is known be positive (i.e. non-negative
/// and non-zero).
bool isKnownPositive(const Value *V, const DataLayout &DL, unsigned Depth = 0,
AssumptionCache *AC = nullptr,
const Instruction *CxtI = nullptr,
const DominatorTree *DT = nullptr);
/// Returns true if the given value is known be negative (i.e. non-positive
/// and non-zero).
bool isKnownNegative(const Value *V, const DataLayout &DL, unsigned Depth = 0,
AssumptionCache *AC = nullptr,
const Instruction *CxtI = nullptr,
const DominatorTree *DT = nullptr);
/// Return true if the given values are known to be non-equal when defined.
/// Supports scalar integer types only.
bool isKnownNonEqual(const Value *V1, const Value *V2, const DataLayout &DL,
AssumptionCache *AC = nullptr,
const Instruction *CxtI = nullptr,
const DominatorTree *DT = nullptr);
/// 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,
const DataLayout &DL,
unsigned Depth = 0, AssumptionCache *AC = nullptr,
const Instruction *CxtI = nullptr,
const DominatorTree *DT = nullptr);
/// 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 mininum number of known sign
/// bits.
unsigned ComputeNumSignBits(const Value *Op, const DataLayout &DL,
unsigned Depth = 0, AssumptionCache *AC = nullptr,
const Instruction *CxtI = nullptr,
const DominatorTree *DT = nullptr);
/// This function computes the integer multiple of Base that equals V. If
/// successful, it returns true and returns the multiple in Multiple. If
/// unsuccessful, it returns false. Also, if V can be simplified to an
/// integer, then the simplified V is returned in Val. Look through sext only
/// if LookThroughSExt=true.
bool ComputeMultiple(Value *V, unsigned Base, Value *&Multiple,
bool LookThroughSExt = false,
unsigned Depth = 0);
/// Map a call instruction to an intrinsic ID. Libcalls which have equivalent
/// intrinsics are treated as-if they were intrinsics.
Intrinsic::ID getIntrinsicForCallSite(ImmutableCallSite ICS,
const TargetLibraryInfo *TLI);
/// Return true if we can prove that the specified FP value is never equal to
/// -0.0.
bool CannotBeNegativeZero(const Value *V, const TargetLibraryInfo *TLI,
unsigned Depth = 0);
/// Return true if we can prove that the specified FP value is either NaN or
/// never less than -0.0.
///
/// NaN --> true
/// +0 --> true
/// -0 --> true
/// x > +0 --> true
/// x < -0 --> false
///
bool CannotBeOrderedLessThanZero(const Value *V, const TargetLibraryInfo *TLI);
/// Return true if we can prove that the specified FP value's sign bit is 0.
///
/// NaN --> true/false (depending on the NaN's sign bit)
/// +0 --> true
/// -0 --> false
/// x > +0 --> true
/// x < -0 --> false
///
bool SignBitMustBeZero(const Value *V, const TargetLibraryInfo *TLI);
/// If the specified value can be set by repeating the same byte in memory,
/// return the i8 value that it is represented with. This is true for all i8
/// values obviously, but is also true for i32 0, i32 -1, i16 0xF0F0, double
/// 0.0 etc. If the value can't be handled with a repeated byte store (e.g.
/// i16 0x1234), return null.
Value *isBytewiseValue(Value *V);
/// Given an aggregrate and an sequence of indices, see if the scalar value
/// indexed is already around as a register, for example if it were inserted
/// directly into the aggregrate.
///
/// If InsertBefore is not null, this function will duplicate (modified)
/// insertvalues when a part of a nested struct is extracted.
Value *FindInsertedValue(Value *V,
ArrayRef<unsigned> idx_range,
Instruction *InsertBefore = nullptr);
/// Analyze the specified pointer to see if it can be expressed as a base
/// pointer plus a constant offset. Return the base and offset to the caller.
Value *GetPointerBaseWithConstantOffset(Value *Ptr, int64_t &Offset,
const DataLayout &DL);
static inline const Value *
GetPointerBaseWithConstantOffset(const Value *Ptr, int64_t &Offset,
const DataLayout &DL) {
return GetPointerBaseWithConstantOffset(const_cast<Value *>(Ptr), Offset,
DL);
}
/// Returns true if the GEP is based on a pointer to a string (array of
// \p CharSize integers) and is indexing into this string.
bool isGEPBasedOnPointerToString(const GEPOperator *GEP,
unsigned CharSize = 8);
/// Represents offset+length into a ConstantDataArray.
struct ConstantDataArraySlice {
/// ConstantDataArray pointer. nullptr indicates a zeroinitializer (a valid
/// initializer, it just doesn't fit the ConstantDataArray interface).
const ConstantDataArray *Array;
/// Slice starts at this Offset.
uint64_t Offset;
/// Length of the slice.
uint64_t Length;
/// Moves the Offset and adjusts Length accordingly.
void move(uint64_t Delta) {
assert(Delta < Length);
Offset += Delta;
Length -= Delta;
}
/// Convenience accessor for elements in the slice.
uint64_t operator[](unsigned I) const {
return Array==nullptr ? 0 : Array->getElementAsInteger(I + Offset);
}
};
/// Returns true if the value \p V is a pointer into a ContantDataArray.
/// If successful \p Index will point to a ConstantDataArray info object
/// with an appropriate offset.
bool getConstantDataArrayInfo(const Value *V, ConstantDataArraySlice &Slice,
unsigned ElementSize, uint64_t Offset = 0);
/// This function computes the length of a null-terminated C string pointed to
/// by V. If successful, it returns true and returns the string in Str. If
/// unsuccessful, it returns false. This does not include the trailing null
/// character by default. If TrimAtNul is set to false, then this returns any
/// trailing null characters as well as any other characters that come after
/// it.
bool getConstantStringInfo(const Value *V, StringRef &Str,
uint64_t Offset = 0, bool TrimAtNul = true);
/// If we can compute the length of the string pointed to by the specified
/// pointer, return 'len+1'. If we can't, return 0.
uint64_t GetStringLength(const Value *V, unsigned CharSize = 8);
/// This method strips off any GEP address adjustments and pointer casts from
/// the specified value, returning the original object being addressed. Note
/// that the returned value has pointer type if the specified value does. If
/// the MaxLookup value is non-zero, it limits the number of instructions to
/// be stripped off.
Value *GetUnderlyingObject(Value *V, const DataLayout &DL,
unsigned MaxLookup = 6);
static inline const Value *GetUnderlyingObject(const Value *V,
const DataLayout &DL,
unsigned MaxLookup = 6) {
return GetUnderlyingObject(const_cast<Value *>(V), DL, MaxLookup);
}
/// \brief This method is similar to GetUnderlyingObject except that it can
/// look through phi and select instructions and return multiple objects.
///
/// If LoopInfo is passed, loop phis are further analyzed. If a pointer
/// accesses different objects in each iteration, we don't look through the
/// phi node. E.g. consider this loop nest:
///
/// int **A;
/// for (i)
/// for (j) {
/// A[i][j] = A[i-1][j] * B[j]
/// }
///
/// This is transformed by Load-PRE to stash away A[i] for the next iteration
/// of the outer loop:
///
/// Curr = A[0]; // Prev_0
/// for (i: 1..N) {
/// Prev = Curr; // Prev = PHI (Prev_0, Curr)
/// Curr = A[i];
/// for (j: 0..N) {
/// Curr[j] = Prev[j] * B[j]
/// }
/// }
///
/// Since A[i] and A[i-1] are independent pointers, getUnderlyingObjects
/// should not assume that Curr and Prev share the same underlying object thus
/// it shouldn't look through the phi above.
void GetUnderlyingObjects(Value *V, SmallVectorImpl<Value *> &Objects,
const DataLayout &DL, LoopInfo *LI = nullptr,
unsigned MaxLookup = 6);
/// Return true if the only users of this pointer are lifetime markers.
bool onlyUsedByLifetimeMarkers(const Value *V);
/// Return true if the instruction does not have any effects besides
/// calculating the result and does not have undefined behavior.
///
/// This method never returns true for an instruction that returns true for
/// mayHaveSideEffects; however, this method also does some other checks in
/// addition. It checks for undefined behavior, like dividing by zero or
/// loading from an invalid pointer (but not for undefined results, like a
/// shift with a shift amount larger than the width of the result). It checks
/// for malloc and alloca because speculatively executing them might cause a
/// memory leak. It also returns false for instructions related to control
/// flow, specifically terminators and PHI nodes.
///
/// If the CtxI is specified this method performs context-sensitive analysis
/// and returns true if it is safe to execute the instruction immediately
/// before the CtxI.
///
/// If the CtxI is NOT specified this method only looks at the instruction
/// itself and its operands, so if this method returns true, it is safe to
/// move the instruction as long as the correct dominance relationships for
/// the operands and users hold.
///
/// This method can return true for instructions that read memory;
/// for such instructions, moving them may change the resulting value.
bool isSafeToSpeculativelyExecute(const Value *V,
const Instruction *CtxI = nullptr,
const DominatorTree *DT = nullptr);
/// Returns true if the result or effects of the given instructions \p I
/// depend on or influence global memory.
/// Memory dependence arises for example if the instruction reads from
/// memory or may produce effects or undefined behaviour. Memory dependent
/// instructions generally cannot be reorderd with respect to other memory
/// dependent instructions or moved into non-dominated basic blocks.
/// Instructions which just compute a value based on the values of their
/// operands are not memory dependent.
bool mayBeMemoryDependent(const Instruction &I);
/// Return true if this pointer couldn't possibly be null by its definition.
/// This returns true for allocas, non-extern-weak globals, and byval
/// arguments.
bool isKnownNonNull(const Value *V);
/// Return true if this pointer couldn't possibly be null. 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.
bool isKnownNonNullAt(const Value *V,
const Instruction *CtxI = nullptr,
const DominatorTree *DT = nullptr);
/// Return true if it is valid to use the assumptions provided by an
/// assume intrinsic, I, at the point in the control-flow identified by the
/// context instruction, CxtI.
bool isValidAssumeForContext(const Instruction *I, const Instruction *CxtI,
const DominatorTree *DT = nullptr);
enum class OverflowResult { AlwaysOverflows, MayOverflow, NeverOverflows };
OverflowResult computeOverflowForUnsignedMul(const Value *LHS,
const Value *RHS,
const DataLayout &DL,
AssumptionCache *AC,
const Instruction *CxtI,
const DominatorTree *DT);
OverflowResult computeOverflowForUnsignedAdd(const Value *LHS,
const Value *RHS,
const DataLayout &DL,
AssumptionCache *AC,
const Instruction *CxtI,
const DominatorTree *DT);
OverflowResult computeOverflowForSignedAdd(const Value *LHS, const Value *RHS,
const DataLayout &DL,
AssumptionCache *AC = nullptr,
const Instruction *CxtI = nullptr,
const DominatorTree *DT = nullptr);
/// This version also leverages the sign bit of Add if known.
OverflowResult computeOverflowForSignedAdd(const AddOperator *Add,
const DataLayout &DL,
AssumptionCache *AC = nullptr,
const Instruction *CxtI = nullptr,
const DominatorTree *DT = nullptr);
/// Returns true if the arithmetic part of the \p II 's result is
/// used only along the paths control dependent on the computation
/// not overflowing, \p II being an <op>.with.overflow intrinsic.
bool isOverflowIntrinsicNoWrap(const IntrinsicInst *II,
const DominatorTree &DT);
/// Return true if this function can prove that the instruction I will
/// always transfer execution to one of its successors (including the next
/// instruction that follows within a basic block). E.g. this is not
/// guaranteed for function calls that could loop infinitely.
///
/// In other words, this function returns false for instructions that may
/// transfer execution or fail to transfer execution in a way that is not
/// captured in the CFG nor in the sequence of instructions within a basic
/// block.
///
/// Undefined behavior is assumed not to happen, so e.g. division is
/// guaranteed to transfer execution to the following instruction even
/// though division by zero might cause undefined behavior.
bool isGuaranteedToTransferExecutionToSuccessor(const Instruction *I);
/// Return true if this function can prove that the instruction I
/// is executed for every iteration of the loop L.
///
/// Note that this currently only considers the loop header.
bool isGuaranteedToExecuteForEveryIteration(const Instruction *I,
const Loop *L);
/// Return true if this function can prove that I is guaranteed to yield
/// full-poison (all bits poison) if at least one of its operands are
/// full-poison (all bits poison).
///
/// The exact rules for how poison propagates through instructions have
/// not been settled as of 2015-07-10, so this function is conservative
/// and only considers poison to be propagated in uncontroversial
/// cases. There is no attempt to track values that may be only partially
/// poison.
bool propagatesFullPoison(const Instruction *I);
/// Return either nullptr or an operand of I such that I will trigger
/// undefined behavior if I is executed and that operand has a full-poison
/// value (all bits poison).
const Value *getGuaranteedNonFullPoisonOp(const Instruction *I);
/// Return true if this function can prove that if PoisonI is executed
/// and yields a full-poison value (all bits poison), then that will
/// trigger undefined behavior.
///
/// Note that this currently only considers the basic block that is
/// the parent of I.
bool programUndefinedIfFullPoison(const Instruction *PoisonI);
/// \brief Specific patterns of select instructions we can match.
enum SelectPatternFlavor {
SPF_UNKNOWN = 0,
SPF_SMIN, /// Signed minimum
SPF_UMIN, /// Unsigned minimum
SPF_SMAX, /// Signed maximum
SPF_UMAX, /// Unsigned maximum
SPF_FMINNUM, /// Floating point minnum
SPF_FMAXNUM, /// Floating point maxnum
SPF_ABS, /// Absolute value
SPF_NABS /// Negated absolute value
};
/// \brief Behavior when a floating point min/max is given one NaN and one
/// non-NaN as input.
enum SelectPatternNaNBehavior {
SPNB_NA = 0, /// NaN behavior not applicable.
SPNB_RETURNS_NAN, /// Given one NaN input, returns the NaN.
SPNB_RETURNS_OTHER, /// Given one NaN input, returns the non-NaN.
SPNB_RETURNS_ANY /// Given one NaN input, can return either (or
/// it has been determined that no operands can
/// be NaN).
};
struct SelectPatternResult {
SelectPatternFlavor Flavor;
SelectPatternNaNBehavior NaNBehavior; /// Only applicable if Flavor is
/// SPF_FMINNUM or SPF_FMAXNUM.
bool Ordered; /// When implementing this min/max pattern as
/// fcmp; select, does the fcmp have to be
/// ordered?
/// \brief Return true if \p SPF is a min or a max pattern.
static bool isMinOrMax(SelectPatternFlavor SPF) {
return !(SPF == SPF_UNKNOWN || SPF == SPF_ABS || SPF == SPF_NABS);
}
};
/// Pattern match integer [SU]MIN, [SU]MAX and ABS idioms, returning the kind
/// and providing the out parameter results if we successfully match.
///
/// If CastOp is not nullptr, also match MIN/MAX idioms where the type does
/// not match that of the original select. If this is the case, the cast
/// operation (one of Trunc,SExt,Zext) that must be done to transform the
/// type of LHS and RHS into the type of V is returned in CastOp.
///
/// For example:
/// %1 = icmp slt i32 %a, i32 4
/// %2 = sext i32 %a to i64
/// %3 = select i1 %1, i64 %2, i64 4
///
/// -> LHS = %a, RHS = i32 4, *CastOp = Instruction::SExt
///
SelectPatternResult matchSelectPattern(Value *V, Value *&LHS, Value *&RHS,
Instruction::CastOps *CastOp = nullptr);
static inline SelectPatternResult
matchSelectPattern(const Value *V, const Value *&LHS, const Value *&RHS,
Instruction::CastOps *CastOp = nullptr) {
Value *L = const_cast<Value*>(LHS);
Value *R = const_cast<Value*>(RHS);
auto Result = matchSelectPattern(const_cast<Value*>(V), L, R);
LHS = L;
RHS = R;
return Result;
}
/// Return true if RHS is known to be implied true by LHS. Return false if
/// RHS is known to be implied false by LHS. Otherwise, return None if no
/// implication can be made.
/// A & B must be i1 (boolean) values or a vector of such values. Note that
/// the truth table for implication is the same as <=u on i1 values (but not
/// <=s!). The truth table for both is:
/// | T | F (B)
/// T | T | F
/// F | T | T
/// (A)
Optional<bool> isImpliedCondition(const Value *LHS, const Value *RHS,
const DataLayout &DL,
bool InvertAPred = false,
unsigned Depth = 0,
AssumptionCache *AC = nullptr,
const Instruction *CxtI = nullptr,
const DominatorTree *DT = nullptr);
} // end namespace llvm
#endif