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