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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/System/DataTypes.h"
#include <string>
namespace llvm {
template <typename T> class SmallVectorImpl;
class Value;
class Instruction;
class APInt;
class TargetData;
/// ComputeMaskedBits - Determine which of the bits specified in Mask are
/// known to be either zero or one and return them in the KnownZero/KnownOne
/// bit sets. This code only analyzes bits in Mask, in order to short-circuit
/// processing.
///
/// 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.
void ComputeMaskedBits(Value *V, const APInt &Mask, APInt &KnownZero,
APInt &KnownOne, const TargetData *TD = 0,
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 TargetData *TD = 0, 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 TargetData *TD = 0,
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);
/// DecomposeGEPExpression - If V is a symbolic pointer expression, decompose
/// it into a base pointer with a constant offset and a number of scaled
/// symbolic offsets.
///
/// The scaled symbolic offsets (represented by pairs of a Value* and a scale
/// in the VarIndices vector) are Value*'s that are known to be scaled by the
/// specified amount, but which may have other unrepresented high bits. As
/// such, the gep cannot necessarily be reconstructed from its decomposed
/// form.
///
/// When TargetData is around, this function is capable of analyzing
/// everything that Value::getUnderlyingObject() can look through. When not,
/// it just looks through pointer casts.
///
const Value *DecomposeGEPExpression(const Value *V, int64_t &BaseOffs,
SmallVectorImpl<std::pair<const Value*, int64_t> > &VarIndices,
const TargetData *TD);
/// FindScalarValue - 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,
const unsigned *idx_begin,
const unsigned *idx_end,
Instruction *InsertBefore = 0);
/// This is a convenience wrapper for finding values indexed by a single index
/// only.
inline Value *FindInsertedValue(Value *V, const unsigned Idx,
Instruction *InsertBefore = 0) {
const unsigned Idxs[1] = { Idx };
return FindInsertedValue(V, &Idxs[0], &Idxs[1], InsertBefore);
}
/// 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. If
/// StopAtNul is set to true (the default), the returned string is truncated
/// by a nul character in the global. If StopAtNul is false, the nul
/// character is included in the result string.
bool GetConstantStringInfo(Value *V, std::string &Str, uint64_t Offset = 0,
bool StopAtNul = 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);
} // end namespace llvm
#endif
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