1//===- llvm/Analysis/ValueTracking.h - Walk computations --------*- C++ -*-===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file contains routines that help analyze properties that chains of
11// computations have.
12//
13//===----------------------------------------------------------------------===//
14
15#ifndef LLVM_ANALYSIS_VALUETRACKING_H
16#define LLVM_ANALYSIS_VALUETRACKING_H
17
18#include "llvm/ADT/ArrayRef.h"
19#include "llvm/Support/DataTypes.h"
20
21namespace llvm {
22  class Value;
23  class Instruction;
24  class APInt;
25  class DataLayout;
26  class StringRef;
27  class MDNode;
28  class AssumptionCache;
29  class DominatorTree;
30  class TargetLibraryInfo;
31
32  /// Determine which bits of V are known to be either zero or one and return
33  /// them in the KnownZero/KnownOne bit sets.
34  ///
35  /// This function is defined on values with integer type, values with pointer
36  /// type, 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 &DL, 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,
48                                         APInt &KnownZero);
49
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 &DL, unsigned Depth = 0,
54                      AssumptionCache *AC = nullptr,
55                      const Instruction *CxtI = nullptr,
56                      const DominatorTree *DT = nullptr);
57
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, const DataLayout &DL,
64                              bool OrZero = false, unsigned Depth = 0,
65                              AssumptionCache *AC = nullptr,
66                              const Instruction *CxtI = nullptr,
67                              const DominatorTree *DT = nullptr);
68
69  /// isKnownNonZero - Return true if the given value is known to be non-zero
70  /// when defined.  For vectors return true if every element is known to be
71  /// non-zero when defined.  Supports values with integer or pointer type and
72  /// vectors of integers.
73  bool isKnownNonZero(Value *V, const DataLayout &DL, unsigned Depth = 0,
74                      AssumptionCache *AC = nullptr,
75                      const Instruction *CxtI = nullptr,
76                      const DominatorTree *DT = nullptr);
77
78  /// MaskedValueIsZero - Return true if 'V & Mask' is known to be zero.  We use
79  /// this predicate to simplify operations downstream.  Mask is known to be
80  /// zero for bits that V cannot have.
81  ///
82  /// This function is defined on values with integer type, values with pointer
83  /// type, and vectors of integers.  In the case
84  /// where V is a vector, the mask, known zero, and known one values are the
85  /// same width as the vector element, and the bit is set only if it is true
86  /// for all of the elements in the vector.
87  bool MaskedValueIsZero(Value *V, const APInt &Mask, const DataLayout &DL,
88                         unsigned Depth = 0, AssumptionCache *AC = nullptr,
89                         const Instruction *CxtI = nullptr,
90                         const DominatorTree *DT = nullptr);
91
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.
97  ///
98  /// 'Op' must have a scalar integer type.
99  ///
100  unsigned ComputeNumSignBits(Value *Op, const DataLayout &DL,
101                              unsigned Depth = 0, AssumptionCache *AC = nullptr,
102                              const Instruction *CxtI = nullptr,
103                              const DominatorTree *DT = nullptr);
104
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,
112                       unsigned Depth = 0);
113
114  /// CannotBeNegativeZero - Return true if we can prove that the specified FP
115  /// value is never equal to -0.0.
116  ///
117  bool CannotBeNegativeZero(const Value *V, unsigned Depth = 0);
118
119  /// CannotBeOrderedLessThanZero - Return true if we can prove that the
120  /// specified FP value is either a NaN or never less than 0.0.
121  ///
122  bool CannotBeOrderedLessThanZero(const Value *V, unsigned Depth = 0);
123
124  /// isBytewiseValue - If the specified value can be set by repeating the same
125  /// byte in memory, return the i8 value that it is represented with.  This is
126  /// true for all i8 values obviously, but is also true for i32 0, i32 -1,
127  /// i16 0xF0F0, double 0.0 etc.  If the value can't be handled with a repeated
128  /// byte store (e.g. i16 0x1234), return null.
129  Value *isBytewiseValue(Value *V);
130
131  /// FindInsertedValue - Given an aggregrate and an sequence of indices, see if
132  /// the scalar value indexed is already around as a register, for example if
133  /// it were inserted directly into the aggregrate.
134  ///
135  /// If InsertBefore is not null, this function will duplicate (modified)
136  /// insertvalues when a part of a nested struct is extracted.
137  Value *FindInsertedValue(Value *V,
138                           ArrayRef<unsigned> idx_range,
139                           Instruction *InsertBefore = nullptr);
140
141  /// GetPointerBaseWithConstantOffset - Analyze the specified pointer to see if
142  /// it can be expressed as a base pointer plus a constant offset.  Return the
143  /// base and offset to the caller.
144  Value *GetPointerBaseWithConstantOffset(Value *Ptr, int64_t &Offset,
145                                          const DataLayout &DL);
146  static inline const Value *
147  GetPointerBaseWithConstantOffset(const Value *Ptr, int64_t &Offset,
148                                   const DataLayout &DL) {
149    return GetPointerBaseWithConstantOffset(const_cast<Value *>(Ptr), Offset,
150                                            DL);
151  }
152
153  /// getConstantStringInfo - This function computes the length of a
154  /// null-terminated C string pointed to by V.  If successful, it returns true
155  /// and returns the string in Str.  If unsuccessful, it returns false.  This
156  /// does not include the trailing nul character by default.  If TrimAtNul is
157  /// set to false, then this returns any trailing nul characters as well as any
158  /// other characters that come after it.
159  bool getConstantStringInfo(const Value *V, StringRef &Str,
160                             uint64_t Offset = 0, bool TrimAtNul = true);
161
162  /// GetStringLength - If we can compute the length of the string pointed to by
163  /// the specified pointer, return 'len+1'.  If we can't, return 0.
164  uint64_t GetStringLength(Value *V);
165
166  /// GetUnderlyingObject - This method strips off any GEP address adjustments
167  /// and pointer casts from the specified value, returning the original object
168  /// being addressed.  Note that the returned value has pointer type if the
169  /// specified value does.  If the MaxLookup value is non-zero, it limits the
170  /// number of instructions to be stripped off.
171  Value *GetUnderlyingObject(Value *V, const DataLayout &DL,
172                             unsigned MaxLookup = 6);
173  static inline const Value *GetUnderlyingObject(const Value *V,
174                                                 const DataLayout &DL,
175                                                 unsigned MaxLookup = 6) {
176    return GetUnderlyingObject(const_cast<Value *>(V), DL, MaxLookup);
177  }
178
179  /// GetUnderlyingObjects - This method is similar to GetUnderlyingObject
180  /// except that it can look through phi and select instructions and return
181  /// multiple objects.
182  void GetUnderlyingObjects(Value *V, SmallVectorImpl<Value *> &Objects,
183                            const DataLayout &DL, unsigned MaxLookup = 6);
184
185  /// onlyUsedByLifetimeMarkers - Return true if the only users of this pointer
186  /// are lifetime markers.
187  bool onlyUsedByLifetimeMarkers(const Value *V);
188
189  /// isSafeToSpeculativelyExecute - Return true if the instruction does not
190  /// have any effects besides calculating the result and does not have
191  /// undefined behavior.
192  ///
193  /// This method never returns true for an instruction that returns true for
194  /// mayHaveSideEffects; however, this method also does some other checks in
195  /// addition. It checks for undefined behavior, like dividing by zero or
196  /// loading from an invalid pointer (but not for undefined results, like a
197  /// shift with a shift amount larger than the width of the result). It checks
198  /// for malloc and alloca because speculatively executing them might cause a
199  /// memory leak. It also returns false for instructions related to control
200  /// flow, specifically terminators and PHI nodes.
201  ///
202  /// This method only looks at the instruction itself and its operands, so if
203  /// this method returns true, it is safe to move the instruction as long as
204  /// the correct dominance relationships for the operands and users hold.
205  /// However, this method can return true for instructions that read memory;
206  /// for such instructions, moving them may change the resulting value.
207  bool isSafeToSpeculativelyExecute(const Value *V);
208
209  /// isKnownNonNull - Return true if this pointer couldn't possibly be null by
210  /// its definition.  This returns true for allocas, non-extern-weak globals
211  /// and byval arguments.
212  bool isKnownNonNull(const Value *V, const TargetLibraryInfo *TLI = nullptr);
213
214  /// Return true if it is valid to use the assumptions provided by an
215  /// assume intrinsic, I, at the point in the control-flow identified by the
216  /// context instruction, CxtI.
217  bool isValidAssumeForContext(const Instruction *I, const Instruction *CxtI,
218                               const DominatorTree *DT = nullptr);
219
220  enum class OverflowResult { AlwaysOverflows, MayOverflow, NeverOverflows };
221  OverflowResult computeOverflowForUnsignedMul(Value *LHS, Value *RHS,
222                                               const DataLayout &DL,
223                                               AssumptionCache *AC,
224                                               const Instruction *CxtI,
225                                               const DominatorTree *DT);
226  OverflowResult computeOverflowForUnsignedAdd(Value *LHS, Value *RHS,
227                                               const DataLayout &DL,
228                                               AssumptionCache *AC,
229                                               const Instruction *CxtI,
230                                               const DominatorTree *DT);
231} // end namespace llvm
232
233#endif
234