ValueTracking.h revision fc6d3a49867cd38954dc40936a88f1907252c6d2 
1//===- llvm/Analysis/ValueTracking.h - Walk computations --------*- C++ -*-===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file contains routines that help analyze properties that chains of
11// computations have.
12//
13//===----------------------------------------------------------------------===//
14
15#ifndef LLVM_ANALYSIS_VALUETRACKING_H
16#define LLVM_ANALYSIS_VALUETRACKING_H
17
18#include "llvm/ADT/ArrayRef.h"
19#include "llvm/Support/DataTypes.h"
20#include <string>
21
22namespace llvm {
23  template <typename T> class SmallVectorImpl;
24  class Value;
25  class Instruction;
26  class APInt;
27  class TargetData;
28
29  /// ComputeMaskedBits - Determine which of the bits specified in Mask are
30  /// known to be either zero or one and return them in the KnownZero/KnownOne
31  /// bit sets.  This code only analyzes bits in Mask, in order to short-circuit
32  /// processing.
33  ///
34  /// This function is defined on values with integer type, values with pointer
35  /// type (but only if TD is non-null), and vectors of integers.  In the case
36  /// where V is a vector, the mask, known zero, and known one values are the
37  /// same width as the vector element, and the bit is set only if it is true
38  /// for all of the elements in the vector.
39  void ComputeMaskedBits(Value *V, const APInt &Mask, APInt &KnownZero,
40                         APInt &KnownOne, const TargetData *TD = 0,
41                         unsigned Depth = 0);
42
43  /// ComputeSignBit - Determine whether the sign bit is known to be zero or
44  /// one.  Convenience wrapper around ComputeMaskedBits.
45  void ComputeSignBit(Value *V, bool &KnownZero, bool &KnownOne,
46                      const TargetData *TD = 0, unsigned Depth = 0);
47
48  /// isPowerOfTwo - Return true if the given value is known to have exactly one
49  /// bit set when defined. For vectors return true if every element is known to
50  /// be a power of two when defined.  Supports values with integer or pointer
51  /// type and vectors of integers.
52  bool isPowerOfTwo(Value *V, const TargetData *TD = 0, unsigned Depth = 0);
53
54  /// isKnownNonZero - Return true if the given value is known to be non-zero
55  /// when defined.  For vectors return true if every element is known to be
56  /// non-zero when defined.  Supports values with integer or pointer type and
57  /// vectors of integers.
58  bool isKnownNonZero(Value *V, const TargetData *TD = 0, unsigned Depth = 0);
59
60  /// MaskedValueIsZero - Return true if 'V & Mask' is known to be zero.  We use
61  /// this predicate to simplify operations downstream.  Mask is known to be
62  /// zero for bits that V cannot have.
63  ///
64  /// This function is defined on values with integer type, values with pointer
65  /// type (but only if TD is non-null), and vectors of integers.  In the case
66  /// where V is a vector, the mask, known zero, and known one values are the
67  /// same width as the vector element, and the bit is set only if it is true
68  /// for all of the elements in the vector.
69  bool MaskedValueIsZero(Value *V, const APInt &Mask,
70                         const TargetData *TD = 0, unsigned Depth = 0);
71
72
73  /// ComputeNumSignBits - Return the number of times the sign bit of the
74  /// register is replicated into the other bits.  We know that at least 1 bit
75  /// is always equal to the sign bit (itself), but other cases can give us
76  /// information.  For example, immediately after an "ashr X, 2", we know that
77  /// the top 3 bits are all equal to each other, so we return 3.
78  ///
79  /// 'Op' must have a scalar integer type.
80  ///
81  unsigned ComputeNumSignBits(Value *Op, const TargetData *TD = 0,
82                              unsigned Depth = 0);
83
84  /// ComputeMultiple - This function computes the integer multiple of Base that
85  /// equals V.  If successful, it returns true and returns the multiple in
86  /// Multiple.  If unsuccessful, it returns false.  Also, if V can be
87  /// simplified to an integer, then the simplified V is returned in Val.  Look
88  /// through sext only if LookThroughSExt=true.
89  bool ComputeMultiple(Value *V, unsigned Base, Value *&Multiple,
90                       bool LookThroughSExt = false,
91                       unsigned Depth = 0);
92
93  /// CannotBeNegativeZero - Return true if we can prove that the specified FP
94  /// value is never equal to -0.0.
95  ///
96  bool CannotBeNegativeZero(const Value *V, unsigned Depth = 0);
97
98  /// isBytewiseValue - If the specified value can be set by repeating the same
99  /// byte in memory, return the i8 value that it is represented with.  This is
100  /// true for all i8 values obviously, but is also true for i32 0, i32 -1,
101  /// i16 0xF0F0, double 0.0 etc.  If the value can't be handled with a repeated
102  /// byte store (e.g. i16 0x1234), return null.
103  Value *isBytewiseValue(Value *V);
104
105  /// FindInsertedValue - Given an aggregrate and an sequence of indices, see if
106  /// the scalar value indexed is already around as a register, for example if
107  /// it were inserted directly into the aggregrate.
108  ///
109  /// If InsertBefore is not null, this function will duplicate (modified)
110  /// insertvalues when a part of a nested struct is extracted.
111  Value *FindInsertedValue(Value *V,
112                           ArrayRef<unsigned> idx_range,
113                           Instruction *InsertBefore = 0);
114
115  /// GetPointerBaseWithConstantOffset - Analyze the specified pointer to see if
116  /// it can be expressed as a base pointer plus a constant offset.  Return the
117  /// base and offset to the caller.
118  Value *GetPointerBaseWithConstantOffset(Value *Ptr, int64_t &Offset,
119                                          const TargetData &TD);
120  static inline const Value *
121  GetPointerBaseWithConstantOffset(const Value *Ptr, int64_t &Offset,
122                                   const TargetData &TD) {
123    return GetPointerBaseWithConstantOffset(const_cast<Value*>(Ptr), Offset,TD);
124  }
125
126  /// GetConstantStringInfo - This function computes the length of a
127  /// null-terminated C string pointed to by V.  If successful, it returns true
128  /// and returns the string in Str.  If unsuccessful, it returns false.  If
129  /// StopAtNul is set to true (the default), the returned string is truncated
130  /// by a nul character in the global.  If StopAtNul is false, the nul
131  /// character is included in the result string.
132  bool GetConstantStringInfo(const Value *V, std::string &Str,
133                             uint64_t Offset = 0,
134                             bool StopAtNul = true);
135
136  /// GetStringLength - If we can compute the length of the string pointed to by
137  /// the specified pointer, return 'len+1'.  If we can't, return 0.
138  uint64_t GetStringLength(Value *V);
139
140  /// GetUnderlyingObject - This method strips off any GEP address adjustments
141  /// and pointer casts from the specified value, returning the original object
142  /// being addressed.  Note that the returned value has pointer type if the
143  /// specified value does.  If the MaxLookup value is non-zero, it limits the
144  /// number of instructions to be stripped off.
145  Value *GetUnderlyingObject(Value *V, const TargetData *TD = 0,
146                             unsigned MaxLookup = 6);
147  static inline const Value *
148  GetUnderlyingObject(const Value *V, const TargetData *TD = 0,
149                      unsigned MaxLookup = 6) {
150    return GetUnderlyingObject(const_cast<Value *>(V), TD, MaxLookup);
151  }
152
153  /// onlyUsedByLifetimeMarkers - Return true if the only users of this pointer
154  /// are lifetime markers.
155  bool onlyUsedByLifetimeMarkers(const Value *V);
156
157} // end namespace llvm
158
159#endif
160