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