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//===- 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/ADT/ArrayRef.h"
#include "llvm/Support/DataTypes.h"
namespace llvm {
class Value;
class Instruction;
class APInt;
class DataLayout;
class StringRef;
class MDNode;
class TargetLibraryInfo;
/// 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 (but only if TD is non-null), 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(Value *V, APInt &KnownZero, APInt &KnownOne,
const DataLayout *TD = nullptr, unsigned Depth = 0);
void computeKnownBitsLoad(const MDNode &Ranges, APInt &KnownZero);
/// ComputeSignBit - Determine whether the sign bit is known to be zero or
/// one. Convenience wrapper around computeKnownBits.
void ComputeSignBit(Value *V, bool &KnownZero, bool &KnownOne,
const DataLayout *TD = nullptr, unsigned Depth = 0);
/// isKnownToBeAPowerOfTwo - 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
/// returns true if the given value is either a power of two or zero.
bool isKnownToBeAPowerOfTwo(Value *V, bool OrZero = false, unsigned Depth = 0);
/// isKnownNonZero - Return true if the given value is known to be non-zero
/// when defined. For vectors return true if every element is known to be
/// non-zero when defined. Supports values with integer or pointer type and
/// vectors of integers.
bool isKnownNonZero(Value *V, const DataLayout *TD = nullptr,
unsigned Depth = 0);
/// MaskedValueIsZero - Return true if 'V & Mask' is known to be zero. We use
/// this predicate to simplify operations downstream. Mask is known to be
/// zero for bits that V cannot have.
///
/// This function is defined on values with integer type, values with pointer
/// type (but only if TD is non-null), and vectors of integers. In the case
/// where V is a vector, the mask, known zero, and known one values are the
/// same width as the vector element, and the bit is set only if it is true
/// for all of the elements in the vector.
bool MaskedValueIsZero(Value *V, const APInt &Mask,
const DataLayout *TD = nullptr, unsigned Depth = 0);
/// ComputeNumSignBits - Return the number of times the sign bit of the
/// register is replicated into the other bits. We know that at least 1 bit
/// is always equal to the sign bit (itself), but other cases can give us
/// information. For example, immediately after an "ashr X, 2", we know that
/// the top 3 bits are all equal to each other, so we return 3.
///
/// 'Op' must have a scalar integer type.
///
unsigned ComputeNumSignBits(Value *Op, const DataLayout *TD = nullptr,
unsigned Depth = 0);
/// ComputeMultiple - 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);
/// CannotBeNegativeZero - Return true if we can prove that the specified FP
/// value is never equal to -0.0.
///
bool CannotBeNegativeZero(const Value *V, unsigned Depth = 0);
/// isBytewiseValue - If the specified value can be set by repeating the same
/// byte in memory, return the i8 value that it is represented with. This is
/// true for all i8 values obviously, but is also true for i32 0, i32 -1,
/// i16 0xF0F0, double 0.0 etc. If the value can't be handled with a repeated
/// byte store (e.g. i16 0x1234), return null.
Value *isBytewiseValue(Value *V);
/// FindInsertedValue - 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);
/// GetPointerBaseWithConstantOffset - 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 *TD);
static inline const Value *
GetPointerBaseWithConstantOffset(const Value *Ptr, int64_t &Offset,
const DataLayout *TD) {
return GetPointerBaseWithConstantOffset(const_cast<Value*>(Ptr), Offset,TD);
}
/// getConstantStringInfo - 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 nul character by default. If TrimAtNul is
/// set to false, then this returns any trailing nul 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);
/// GetStringLength - 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(Value *V);
/// GetUnderlyingObject - 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 *TD = nullptr,
unsigned MaxLookup = 6);
static inline const Value *
GetUnderlyingObject(const Value *V, const DataLayout *TD = nullptr,
unsigned MaxLookup = 6) {
return GetUnderlyingObject(const_cast<Value *>(V), TD, MaxLookup);
}
/// GetUnderlyingObjects - This method is similar to GetUnderlyingObject
/// except that it can look through phi and select instructions and return
/// multiple objects.
void GetUnderlyingObjects(Value *V,
SmallVectorImpl<Value *> &Objects,
const DataLayout *TD = nullptr,
unsigned MaxLookup = 6);
/// onlyUsedByLifetimeMarkers - Return true if the only users of this pointer
/// are lifetime markers.
bool onlyUsedByLifetimeMarkers(const Value *V);
/// isSafeToSpeculativelyExecute - 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.
///
/// 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.
/// However, 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 DataLayout *TD = nullptr);
/// isKnownNonNull - 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, const TargetLibraryInfo *TLI = nullptr);
} // end namespace llvm
#endif
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