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