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"
23 template <typename T> class SmallVectorImpl;
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, const APInt &Mask, APInt &KnownZero,
40 APInt &KnownOne, const TargetData *TD = 0,
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 TargetData *TD = 0, unsigned Depth = 0);
48 /// isPowerOfTwo - Return true if the given value is known to have exactly one
49 /// bit set when defined. For vectors return true if every element is known to
50 /// be a power of two when defined. Supports values with integer or pointer
51 /// type and vectors of integers. If 'OrZero' is set then returns true if the
52 /// given value is either a power of two or zero.
53 bool isPowerOfTwo(Value *V, const TargetData *TD = 0, bool OrZero = false,
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 TargetData *TD = 0, unsigned Depth = 0);
62 /// MaskedValueIsZero - Return true if 'V & Mask' is known to be zero. We use
63 /// this predicate to simplify operations downstream. Mask is known to be
64 /// zero for bits that V cannot have.
66 /// This function is defined on values with integer type, values with pointer
67 /// type (but only if TD is non-null), and vectors of integers. In the case
68 /// where V is a vector, the mask, known zero, and known one values are the
69 /// same width as the vector element, and the bit is set only if it is true
70 /// for all of the elements in the vector.
71 bool MaskedValueIsZero(Value *V, const APInt &Mask,
72 const TargetData *TD = 0, unsigned Depth = 0);
75 /// ComputeNumSignBits - Return the number of times the sign bit of the
76 /// register is replicated into the other bits. We know that at least 1 bit
77 /// is always equal to the sign bit (itself), but other cases can give us
78 /// information. For example, immediately after an "ashr X, 2", we know that
79 /// the top 3 bits are all equal to each other, so we return 3.
81 /// 'Op' must have a scalar integer type.
83 unsigned ComputeNumSignBits(Value *Op, const TargetData *TD = 0,
86 /// ComputeMultiple - This function computes the integer multiple of Base that
87 /// equals V. If successful, it returns true and returns the multiple in
88 /// Multiple. If unsuccessful, it returns false. Also, if V can be
89 /// simplified to an integer, then the simplified V is returned in Val. Look
90 /// through sext only if LookThroughSExt=true.
91 bool ComputeMultiple(Value *V, unsigned Base, Value *&Multiple,
92 bool LookThroughSExt = false,
95 /// CannotBeNegativeZero - Return true if we can prove that the specified FP
96 /// value is never equal to -0.0.
98 bool CannotBeNegativeZero(const Value *V, unsigned Depth = 0);
100 /// isBytewiseValue - If the specified value can be set by repeating the same
101 /// byte in memory, return the i8 value that it is represented with. This is
102 /// true for all i8 values obviously, but is also true for i32 0, i32 -1,
103 /// i16 0xF0F0, double 0.0 etc. If the value can't be handled with a repeated
104 /// byte store (e.g. i16 0x1234), return null.
105 Value *isBytewiseValue(Value *V);
107 /// FindInsertedValue - Given an aggregrate and an sequence of indices, see if
108 /// the scalar value indexed is already around as a register, for example if
109 /// it were inserted directly into the aggregrate.
111 /// If InsertBefore is not null, this function will duplicate (modified)
112 /// insertvalues when a part of a nested struct is extracted.
113 Value *FindInsertedValue(Value *V,
114 ArrayRef<unsigned> idx_range,
115 Instruction *InsertBefore = 0);
117 /// GetPointerBaseWithConstantOffset - Analyze the specified pointer to see if
118 /// it can be expressed as a base pointer plus a constant offset. Return the
119 /// base and offset to the caller.
120 Value *GetPointerBaseWithConstantOffset(Value *Ptr, int64_t &Offset,
121 const TargetData &TD);
122 static inline const Value *
123 GetPointerBaseWithConstantOffset(const Value *Ptr, int64_t &Offset,
124 const TargetData &TD) {
125 return GetPointerBaseWithConstantOffset(const_cast<Value*>(Ptr), Offset,TD);
128 /// GetConstantStringInfo - This function computes the length of a
129 /// null-terminated C string pointed to by V. If successful, it returns true
130 /// and returns the string in Str. If unsuccessful, it returns false. If
131 /// StopAtNul is set to true (the default), the returned string is truncated
132 /// by a nul character in the global. If StopAtNul is false, the nul
133 /// character is included in the result string.
134 bool GetConstantStringInfo(const Value *V, std::string &Str,
136 bool StopAtNul = 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 TargetData *TD = 0,
148 unsigned MaxLookup = 6);
149 static inline const Value *
150 GetUnderlyingObject(const Value *V, const TargetData *TD = 0,
151 unsigned MaxLookup = 6) {
152 return GetUnderlyingObject(const_cast<Value *>(V), TD, MaxLookup);
155 /// onlyUsedByLifetimeMarkers - Return true if the only users of this pointer
156 /// are lifetime markers.
157 bool onlyUsedByLifetimeMarkers(const Value *V);
159 /// isSafeToSpeculativelyExecute - Return true if the instruction does not
160 /// have any effects besides calculating the result and does not have
161 /// undefined behavior.
163 /// This method never returns true for an instruction that returns true for
164 /// mayHaveSideEffects; however, this method also does some other checks in
165 /// addition. It checks for undefined behavior, like dividing by zero or
166 /// loading from an invalid pointer (but not for undefined results, like a
167 /// shift with a shift amount larger than the width of the result). It checks
168 /// for malloc and alloca because speculatively executing them might cause a
169 /// memory leak. It also returns false for instructions related to control
170 /// flow, specifically terminators and PHI nodes.
172 /// This method only looks at the instruction itself and its operands, so if
173 /// this method returns true, it is safe to move the instruction as long as
174 /// the correct dominance relationships for the operands and users hold.
175 /// However, this method can return true for instructions that read memory;
176 /// for such instructions, moving them may change the resulting value.
177 bool isSafeToSpeculativelyExecute(const Value *V,
178 const TargetData *TD = 0);
180 } // end namespace llvm