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