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/ADT/ArrayRef.h"
19 #include "llvm/Support/DataTypes.h"
28 class TargetLibraryInfo;
30 /// Determine which bits of V are known to be either zero or one and return
31 /// them in the KnownZero/KnownOne bit sets.
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 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 computeKnownBits(Value *V, APInt &KnownZero, APInt &KnownOne,
39 const DataLayout *TD = nullptr, unsigned Depth = 0);
40 /// Compute known bits from the range metadata.
41 /// \p KnownZero the set of bits that are known to be zero
42 void computeKnownBitsFromRangeMetadata(const MDNode &Ranges,
45 /// ComputeSignBit - Determine whether the sign bit is known to be zero or
46 /// one. Convenience wrapper around computeKnownBits.
47 void ComputeSignBit(Value *V, bool &KnownZero, bool &KnownOne,
48 const DataLayout *TD = nullptr, unsigned Depth = 0);
50 /// isKnownToBeAPowerOfTwo - Return true if the given value is known to have
51 /// exactly one bit set when defined. For vectors return true if every
52 /// element is known to be a power of two when defined. Supports values with
53 /// integer or pointer type and vectors of integers. If 'OrZero' is set then
54 /// returns true if the given value is either a power of two or zero.
55 bool isKnownToBeAPowerOfTwo(Value *V, bool OrZero = false, unsigned Depth = 0);
57 /// isKnownNonZero - Return true if the given value is known to be non-zero
58 /// when defined. For vectors return true if every element is known to be
59 /// non-zero when defined. Supports values with integer or pointer type and
60 /// vectors of integers.
61 bool isKnownNonZero(Value *V, const DataLayout *TD = nullptr,
64 /// MaskedValueIsZero - Return true if 'V & Mask' is known to be zero. We use
65 /// this predicate to simplify operations downstream. Mask is known to be
66 /// zero for bits that V cannot have.
68 /// This function is defined on values with integer type, values with pointer
69 /// type (but only if TD is non-null), and vectors of integers. In the case
70 /// where V is a vector, the mask, known zero, and known one values are the
71 /// same width as the vector element, and the bit is set only if it is true
72 /// for all of the elements in the vector.
73 bool MaskedValueIsZero(Value *V, const APInt &Mask,
74 const DataLayout *TD = nullptr, unsigned Depth = 0);
77 /// ComputeNumSignBits - Return the number of times the sign bit of the
78 /// register is replicated into the other bits. We know that at least 1 bit
79 /// is always equal to the sign bit (itself), but other cases can give us
80 /// information. For example, immediately after an "ashr X, 2", we know that
81 /// the top 3 bits are all equal to each other, so we return 3.
83 /// 'Op' must have a scalar integer type.
85 unsigned ComputeNumSignBits(Value *Op, const DataLayout *TD = nullptr,
88 /// ComputeMultiple - This function computes the integer multiple of Base that
89 /// equals V. If successful, it returns true and returns the multiple in
90 /// Multiple. If unsuccessful, it returns false. Also, if V can be
91 /// simplified to an integer, then the simplified V is returned in Val. Look
92 /// through sext only if LookThroughSExt=true.
93 bool ComputeMultiple(Value *V, unsigned Base, Value *&Multiple,
94 bool LookThroughSExt = false,
97 /// CannotBeNegativeZero - Return true if we can prove that the specified FP
98 /// value is never equal to -0.0.
100 bool CannotBeNegativeZero(const Value *V, unsigned Depth = 0);
102 /// isBytewiseValue - If the specified value can be set by repeating the same
103 /// byte in memory, return the i8 value that it is represented with. This is
104 /// true for all i8 values obviously, but is also true for i32 0, i32 -1,
105 /// i16 0xF0F0, double 0.0 etc. If the value can't be handled with a repeated
106 /// byte store (e.g. i16 0x1234), return null.
107 Value *isBytewiseValue(Value *V);
109 /// FindInsertedValue - Given an aggregrate and an sequence of indices, see if
110 /// the scalar value indexed is already around as a register, for example if
111 /// it were inserted directly into the aggregrate.
113 /// If InsertBefore is not null, this function will duplicate (modified)
114 /// insertvalues when a part of a nested struct is extracted.
115 Value *FindInsertedValue(Value *V,
116 ArrayRef<unsigned> idx_range,
117 Instruction *InsertBefore = nullptr);
119 /// GetPointerBaseWithConstantOffset - Analyze the specified pointer to see if
120 /// it can be expressed as a base pointer plus a constant offset. Return the
121 /// base and offset to the caller.
122 Value *GetPointerBaseWithConstantOffset(Value *Ptr, int64_t &Offset,
123 const DataLayout *TD);
124 static inline const Value *
125 GetPointerBaseWithConstantOffset(const Value *Ptr, int64_t &Offset,
126 const DataLayout *TD) {
127 return GetPointerBaseWithConstantOffset(const_cast<Value*>(Ptr), Offset,TD);
130 /// getConstantStringInfo - This function computes the length of a
131 /// null-terminated C string pointed to by V. If successful, it returns true
132 /// and returns the string in Str. If unsuccessful, it returns false. This
133 /// does not include the trailing nul character by default. If TrimAtNul is
134 /// set to false, then this returns any trailing nul characters as well as any
135 /// other characters that come after it.
136 bool getConstantStringInfo(const Value *V, StringRef &Str,
137 uint64_t Offset = 0, bool TrimAtNul = true);
139 /// GetStringLength - If we can compute the length of the string pointed to by
140 /// the specified pointer, return 'len+1'. If we can't, return 0.
141 uint64_t GetStringLength(Value *V);
143 /// GetUnderlyingObject - This method strips off any GEP address adjustments
144 /// and pointer casts from the specified value, returning the original object
145 /// being addressed. Note that the returned value has pointer type if the
146 /// specified value does. If the MaxLookup value is non-zero, it limits the
147 /// number of instructions to be stripped off.
148 Value *GetUnderlyingObject(Value *V, const DataLayout *TD = nullptr,
149 unsigned MaxLookup = 6);
150 static inline const Value *
151 GetUnderlyingObject(const Value *V, const DataLayout *TD = nullptr,
152 unsigned MaxLookup = 6) {
153 return GetUnderlyingObject(const_cast<Value *>(V), TD, MaxLookup);
156 /// GetUnderlyingObjects - This method is similar to GetUnderlyingObject
157 /// except that it can look through phi and select instructions and return
158 /// multiple objects.
159 void GetUnderlyingObjects(Value *V,
160 SmallVectorImpl<Value *> &Objects,
161 const DataLayout *TD = nullptr,
162 unsigned MaxLookup = 6);
164 /// onlyUsedByLifetimeMarkers - Return true if the only users of this pointer
165 /// are lifetime markers.
166 bool onlyUsedByLifetimeMarkers(const Value *V);
168 /// isSafeToSpeculativelyExecute - Return true if the instruction does not
169 /// have any effects besides calculating the result and does not have
170 /// undefined behavior.
172 /// This method never returns true for an instruction that returns true for
173 /// mayHaveSideEffects; however, this method also does some other checks in
174 /// addition. It checks for undefined behavior, like dividing by zero or
175 /// loading from an invalid pointer (but not for undefined results, like a
176 /// shift with a shift amount larger than the width of the result). It checks
177 /// for malloc and alloca because speculatively executing them might cause a
178 /// memory leak. It also returns false for instructions related to control
179 /// flow, specifically terminators and PHI nodes.
181 /// This method only looks at the instruction itself and its operands, so if
182 /// this method returns true, it is safe to move the instruction as long as
183 /// the correct dominance relationships for the operands and users hold.
184 /// However, this method can return true for instructions that read memory;
185 /// for such instructions, moving them may change the resulting value.
186 bool isSafeToSpeculativelyExecute(const Value *V,
187 const DataLayout *TD = nullptr);
189 /// isKnownNonNull - Return true if this pointer couldn't possibly be null by
190 /// its definition. This returns true for allocas, non-extern-weak globals
191 /// and byval arguments.
192 bool isKnownNonNull(const Value *V, const TargetLibraryInfo *TLI = nullptr);
194 } // end namespace llvm