LLVM  3.7.0
ValueTracking.h
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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/IR/Instruction.h"
20 #include "llvm/Support/DataTypes.h"
21 
22 namespace llvm {
23  class Value;
24  class Instruction;
25  class APInt;
26  class DataLayout;
27  class StringRef;
28  class MDNode;
29  class AssumptionCache;
30  class DominatorTree;
31  class TargetLibraryInfo;
32  class LoopInfo;
33 
34  /// Determine which bits of V are known to be either zero or one and return
35  /// them in the KnownZero/KnownOne bit sets.
36  ///
37  /// This function is defined on values with integer type, values with pointer
38  /// type, and vectors of integers. In the case
39  /// where V is a vector, the known zero and known one values are the
40  /// same width as the vector element, and the bit is set only if it is true
41  /// for all of the elements in the vector.
42  void computeKnownBits(Value *V, APInt &KnownZero, APInt &KnownOne,
43  const DataLayout &DL, unsigned Depth = 0,
44  AssumptionCache *AC = nullptr,
45  const Instruction *CxtI = nullptr,
46  const DominatorTree *DT = nullptr);
47  /// Compute known bits from the range metadata.
48  /// \p KnownZero the set of bits that are known to be zero
49  void computeKnownBitsFromRangeMetadata(const MDNode &Ranges,
50  APInt &KnownZero);
51  /// Returns true if LHS and RHS have no common bits set.
52  bool haveNoCommonBitsSet(Value *LHS, Value *RHS, const DataLayout &DL,
53  AssumptionCache *AC = nullptr,
54  const Instruction *CxtI = nullptr,
55  const DominatorTree *DT = nullptr);
56 
57  /// ComputeSignBit - Determine whether the sign bit is known to be zero or
58  /// one. Convenience wrapper around computeKnownBits.
59  void ComputeSignBit(Value *V, bool &KnownZero, bool &KnownOne,
60  const DataLayout &DL, unsigned Depth = 0,
61  AssumptionCache *AC = nullptr,
62  const Instruction *CxtI = nullptr,
63  const DominatorTree *DT = nullptr);
64 
65  /// isKnownToBeAPowerOfTwo - Return true if the given value is known to have
66  /// exactly one bit set when defined. For vectors return true if every
67  /// element is known to be a power of two when defined. Supports values with
68  /// integer or pointer type and vectors of integers. If 'OrZero' is set then
69  /// returns true if the given value is either a power of two or zero.
70  bool isKnownToBeAPowerOfTwo(Value *V, const DataLayout &DL,
71  bool OrZero = false, unsigned Depth = 0,
72  AssumptionCache *AC = nullptr,
73  const Instruction *CxtI = nullptr,
74  const DominatorTree *DT = nullptr);
75 
76  /// isKnownNonZero - Return true if the given value is known to be non-zero
77  /// when defined. For vectors return true if every element is known to be
78  /// non-zero when defined. Supports values with integer or pointer type and
79  /// vectors of integers.
80  bool isKnownNonZero(Value *V, const DataLayout &DL, unsigned Depth = 0,
81  AssumptionCache *AC = nullptr,
82  const Instruction *CxtI = nullptr,
83  const DominatorTree *DT = nullptr);
84 
85  /// MaskedValueIsZero - Return true if 'V & Mask' is known to be zero. We use
86  /// this predicate to simplify operations downstream. Mask is known to be
87  /// zero for bits that V cannot have.
88  ///
89  /// This function is defined on values with integer type, values with pointer
90  /// type, and vectors of integers. In the case
91  /// where V is a vector, the mask, known zero, and known one values are the
92  /// same width as the vector element, and the bit is set only if it is true
93  /// for all of the elements in the vector.
94  bool MaskedValueIsZero(Value *V, const APInt &Mask, const DataLayout &DL,
95  unsigned Depth = 0, AssumptionCache *AC = nullptr,
96  const Instruction *CxtI = nullptr,
97  const DominatorTree *DT = nullptr);
98 
99  /// ComputeNumSignBits - Return the number of times the sign bit of the
100  /// register is replicated into the other bits. We know that at least 1 bit
101  /// is always equal to the sign bit (itself), but other cases can give us
102  /// information. For example, immediately after an "ashr X, 2", we know that
103  /// the top 3 bits are all equal to each other, so we return 3.
104  ///
105  /// 'Op' must have a scalar integer type.
106  ///
107  unsigned ComputeNumSignBits(Value *Op, const DataLayout &DL,
108  unsigned Depth = 0, AssumptionCache *AC = nullptr,
109  const Instruction *CxtI = nullptr,
110  const DominatorTree *DT = nullptr);
111 
112  /// ComputeMultiple - This function computes the integer multiple of Base that
113  /// equals V. If successful, it returns true and returns the multiple in
114  /// Multiple. If unsuccessful, it returns false. Also, if V can be
115  /// simplified to an integer, then the simplified V is returned in Val. Look
116  /// through sext only if LookThroughSExt=true.
117  bool ComputeMultiple(Value *V, unsigned Base, Value *&Multiple,
118  bool LookThroughSExt = false,
119  unsigned Depth = 0);
120 
121  /// CannotBeNegativeZero - Return true if we can prove that the specified FP
122  /// value is never equal to -0.0.
123  ///
124  bool CannotBeNegativeZero(const Value *V, unsigned Depth = 0);
125 
126  /// CannotBeOrderedLessThanZero - Return true if we can prove that the
127  /// specified FP value is either a NaN or never less than 0.0.
128  ///
129  bool CannotBeOrderedLessThanZero(const Value *V, unsigned Depth = 0);
130 
131  /// isBytewiseValue - If the specified value can be set by repeating the same
132  /// byte in memory, return the i8 value that it is represented with. This is
133  /// true for all i8 values obviously, but is also true for i32 0, i32 -1,
134  /// i16 0xF0F0, double 0.0 etc. If the value can't be handled with a repeated
135  /// byte store (e.g. i16 0x1234), return null.
136  Value *isBytewiseValue(Value *V);
137 
138  /// FindInsertedValue - Given an aggregrate and an sequence of indices, see if
139  /// the scalar value indexed is already around as a register, for example if
140  /// it were inserted directly into the aggregrate.
141  ///
142  /// If InsertBefore is not null, this function will duplicate (modified)
143  /// insertvalues when a part of a nested struct is extracted.
144  Value *FindInsertedValue(Value *V,
145  ArrayRef<unsigned> idx_range,
146  Instruction *InsertBefore = nullptr);
147 
148  /// GetPointerBaseWithConstantOffset - Analyze the specified pointer to see if
149  /// it can be expressed as a base pointer plus a constant offset. Return the
150  /// base and offset to the caller.
151  Value *GetPointerBaseWithConstantOffset(Value *Ptr, int64_t &Offset,
152  const DataLayout &DL);
153  static inline const Value *
154  GetPointerBaseWithConstantOffset(const Value *Ptr, int64_t &Offset,
155  const DataLayout &DL) {
156  return GetPointerBaseWithConstantOffset(const_cast<Value *>(Ptr), Offset,
157  DL);
158  }
159 
160  /// getConstantStringInfo - This function computes the length of a
161  /// null-terminated C string pointed to by V. If successful, it returns true
162  /// and returns the string in Str. If unsuccessful, it returns false. This
163  /// does not include the trailing nul character by default. If TrimAtNul is
164  /// set to false, then this returns any trailing nul characters as well as any
165  /// other characters that come after it.
166  bool getConstantStringInfo(const Value *V, StringRef &Str,
167  uint64_t Offset = 0, bool TrimAtNul = true);
168 
169  /// GetStringLength - If we can compute the length of the string pointed to by
170  /// the specified pointer, return 'len+1'. If we can't, return 0.
171  uint64_t GetStringLength(Value *V);
172 
173  /// GetUnderlyingObject - This method strips off any GEP address adjustments
174  /// and pointer casts from the specified value, returning the original object
175  /// being addressed. Note that the returned value has pointer type if the
176  /// specified value does. If the MaxLookup value is non-zero, it limits the
177  /// number of instructions to be stripped off.
178  Value *GetUnderlyingObject(Value *V, const DataLayout &DL,
179  unsigned MaxLookup = 6);
180  static inline const Value *GetUnderlyingObject(const Value *V,
181  const DataLayout &DL,
182  unsigned MaxLookup = 6) {
183  return GetUnderlyingObject(const_cast<Value *>(V), DL, MaxLookup);
184  }
185 
186  /// \brief This method is similar to GetUnderlyingObject except that it can
187  /// look through phi and select instructions and return multiple objects.
188  ///
189  /// If LoopInfo is passed, loop phis are further analyzed. If a pointer
190  /// accesses different objects in each iteration, we don't look through the
191  /// phi node. E.g. consider this loop nest:
192  ///
193  /// int **A;
194  /// for (i)
195  /// for (j) {
196  /// A[i][j] = A[i-1][j] * B[j]
197  /// }
198  ///
199  /// This is transformed by Load-PRE to stash away A[i] for the next iteration
200  /// of the outer loop:
201  ///
202  /// Curr = A[0]; // Prev_0
203  /// for (i: 1..N) {
204  /// Prev = Curr; // Prev = PHI (Prev_0, Curr)
205  /// Curr = A[i];
206  /// for (j: 0..N) {
207  /// Curr[j] = Prev[j] * B[j]
208  /// }
209  /// }
210  ///
211  /// Since A[i] and A[i-1] are independent pointers, getUnderlyingObjects
212  /// should not assume that Curr and Prev share the same underlying object thus
213  /// it shouldn't look through the phi above.
214  void GetUnderlyingObjects(Value *V, SmallVectorImpl<Value *> &Objects,
215  const DataLayout &DL, LoopInfo *LI = nullptr,
216  unsigned MaxLookup = 6);
217 
218  /// onlyUsedByLifetimeMarkers - Return true if the only users of this pointer
219  /// are lifetime markers.
220  bool onlyUsedByLifetimeMarkers(const Value *V);
221 
222  /// isDereferenceablePointer - Return true if this is always a dereferenceable
223  /// pointer. If the context instruction is specified perform context-sensitive
224  /// analysis and return true if the pointer is dereferenceable at the
225  /// specified instruction.
226  bool isDereferenceablePointer(const Value *V, const DataLayout &DL,
227  const Instruction *CtxI = nullptr,
228  const DominatorTree *DT = nullptr,
229  const TargetLibraryInfo *TLI = nullptr);
230 
231  /// isSafeToSpeculativelyExecute - Return true if the instruction does not
232  /// have any effects besides calculating the result and does not have
233  /// undefined behavior.
234  ///
235  /// This method never returns true for an instruction that returns true for
236  /// mayHaveSideEffects; however, this method also does some other checks in
237  /// addition. It checks for undefined behavior, like dividing by zero or
238  /// loading from an invalid pointer (but not for undefined results, like a
239  /// shift with a shift amount larger than the width of the result). It checks
240  /// for malloc and alloca because speculatively executing them might cause a
241  /// memory leak. It also returns false for instructions related to control
242  /// flow, specifically terminators and PHI nodes.
243  ///
244  /// If the CtxI is specified this method performs context-sensitive analysis
245  /// and returns true if it is safe to execute the instruction immediately
246  /// before the CtxI.
247  ///
248  /// If the CtxI is NOT specified this method only looks at the instruction
249  /// itself and its operands, so if this method returns true, it is safe to
250  /// move the instruction as long as the correct dominance relationships for
251  /// the operands and users hold.
252  ///
253  /// This method can return true for instructions that read memory;
254  /// for such instructions, moving them may change the resulting value.
255  bool isSafeToSpeculativelyExecute(const Value *V,
256  const Instruction *CtxI = nullptr,
257  const DominatorTree *DT = nullptr,
258  const TargetLibraryInfo *TLI = nullptr);
259 
260  /// isKnownNonNull - Return true if this pointer couldn't possibly be null by
261  /// its definition. This returns true for allocas, non-extern-weak globals
262  /// and byval arguments.
263  bool isKnownNonNull(const Value *V, const TargetLibraryInfo *TLI = nullptr);
264 
265  /// isKnownNonNullAt - Return true if this pointer couldn't possibly be null.
266  /// If the context instruction is specified perform context-sensitive analysis
267  /// and return true if the pointer couldn't possibly be null at the specified
268  /// instruction.
269  bool isKnownNonNullAt(const Value *V,
270  const Instruction *CtxI = nullptr,
271  const DominatorTree *DT = nullptr,
272  const TargetLibraryInfo *TLI = nullptr);
273 
274  /// Return true if it is valid to use the assumptions provided by an
275  /// assume intrinsic, I, at the point in the control-flow identified by the
276  /// context instruction, CxtI.
277  bool isValidAssumeForContext(const Instruction *I, const Instruction *CxtI,
278  const DominatorTree *DT = nullptr);
279 
281  OverflowResult computeOverflowForUnsignedMul(Value *LHS, Value *RHS,
282  const DataLayout &DL,
283  AssumptionCache *AC,
284  const Instruction *CxtI,
285  const DominatorTree *DT);
286  OverflowResult computeOverflowForUnsignedAdd(Value *LHS, Value *RHS,
287  const DataLayout &DL,
288  AssumptionCache *AC,
289  const Instruction *CxtI,
290  const DominatorTree *DT);
291 
292  /// \brief Specific patterns of select instructions we can match.
295  SPF_SMIN, // Signed minimum
296  SPF_UMIN, // Unsigned minimum
297  SPF_SMAX, // Signed maximum
298  SPF_UMAX, // Unsigned maximum
299  SPF_ABS, // Absolute value
300  SPF_NABS // Negated absolute value
301  };
302  /// Pattern match integer [SU]MIN, [SU]MAX and ABS idioms, returning the kind
303  /// and providing the out parameter results if we successfully match.
304  ///
305  /// If CastOp is not nullptr, also match MIN/MAX idioms where the type does
306  /// not match that of the original select. If this is the case, the cast
307  /// operation (one of Trunc,SExt,Zext) that must be done to transform the
308  /// type of LHS and RHS into the type of V is returned in CastOp.
309  ///
310  /// For example:
311  /// %1 = icmp slt i32 %a, i32 4
312  /// %2 = sext i32 %a to i64
313  /// %3 = select i1 %1, i64 %2, i64 4
314  ///
315  /// -> LHS = %a, RHS = i32 4, *CastOp = Instruction::SExt
316  ///
317  SelectPatternFlavor matchSelectPattern(Value *V, Value *&LHS, Value *&RHS,
318  Instruction::CastOps *CastOp = nullptr);
319 
320 } // end namespace llvm
321 
322 #endif
A parsed version of the target data layout string in and methods for querying it. ...
Definition: DataLayout.h:104
uint64_t GetStringLength(Value *V)
GetStringLength - If we can compute the length of the string pointed to by the specified pointer...
Value * isBytewiseValue(Value *V)
isBytewiseValue - If the specified value can be set by repeating the same byte in memory...
void computeKnownBits(Value *V, APInt &KnownZero, APInt &KnownOne, const DataLayout &DL, unsigned Depth=0, AssumptionCache *AC=nullptr, const Instruction *CxtI=nullptr, const DominatorTree *DT=nullptr)
Determine which bits of V are known to be either zero or one and return them in the KnownZero/KnownOn...
bool haveNoCommonBitsSet(Value *LHS, Value *RHS, const DataLayout &DL, AssumptionCache *AC=nullptr, const Instruction *CxtI=nullptr, const DominatorTree *DT=nullptr)
Returns true if LHS and RHS have no common bits set.
bool isValidAssumeForContext(const Instruction *I, const Instruction *CxtI, const DominatorTree *DT=nullptr)
Return true if it is valid to use the assumptions provided by an assume intrinsic, I, at the point in the control-flow identified by the context instruction, CxtI.
void GetUnderlyingObjects(Value *V, SmallVectorImpl< Value * > &Objects, const DataLayout &DL, LoopInfo *LI=nullptr, unsigned MaxLookup=6)
This method is similar to GetUnderlyingObject except that it can look through phi and select instruct...
void computeKnownBitsFromRangeMetadata(const MDNode &Ranges, APInt &KnownZero)
Compute known bits from the range metadata.
SelectPatternFlavor matchSelectPattern(Value *V, Value *&LHS, Value *&RHS, Instruction::CastOps *CastOp=nullptr)
Pattern match integer [SU]MIN, [SU]MAX and ABS idioms, returning the kind and providing the out param...
bool isDereferenceablePointer(const Value *V, const DataLayout &DL, const Instruction *CtxI=nullptr, const DominatorTree *DT=nullptr, const TargetLibraryInfo *TLI=nullptr)
isDereferenceablePointer - Return true if this is always a dereferenceable pointer.
bool MaskedValueIsZero(Value *V, const APInt &Mask, const DataLayout &DL, unsigned Depth=0, AssumptionCache *AC=nullptr, const Instruction *CxtI=nullptr, const DominatorTree *DT=nullptr)
MaskedValueIsZero - Return true if 'V & Mask' is known to be zero.
Value * GetPointerBaseWithConstantOffset(Value *Ptr, int64_t &Offset, const DataLayout &DL)
GetPointerBaseWithConstantOffset - Analyze the specified pointer to see if it can be expressed as a b...
bool isKnownToBeAPowerOfTwo(Value *V, const DataLayout &DL, bool OrZero=false, unsigned Depth=0, AssumptionCache *AC=nullptr, const Instruction *CxtI=nullptr, const DominatorTree *DT=nullptr)
isKnownToBeAPowerOfTwo - Return true if the given value is known to have exactly one bit set when def...
OverflowResult computeOverflowForUnsignedAdd(Value *LHS, Value *RHS, const DataLayout &DL, AssumptionCache *AC, const Instruction *CxtI, const DominatorTree *DT)
bool onlyUsedByLifetimeMarkers(const Value *V)
onlyUsedByLifetimeMarkers - Return true if the only users of this pointer are lifetime markers...
OverflowResult computeOverflowForUnsignedMul(Value *LHS, Value *RHS, const DataLayout &DL, AssumptionCache *AC, const Instruction *CxtI, const DominatorTree *DT)
void ComputeSignBit(Value *V, bool &KnownZero, bool &KnownOne, const DataLayout &DL, unsigned Depth=0, AssumptionCache *AC=nullptr, const Instruction *CxtI=nullptr, const DominatorTree *DT=nullptr)
ComputeSignBit - Determine whether the sign bit is known to be zero or one.
Value * GetUnderlyingObject(Value *V, const DataLayout &DL, unsigned MaxLookup=6)
GetUnderlyingObject - This method strips off any GEP address adjustments and pointer casts from the s...
Value * FindInsertedValue(Value *V, ArrayRef< unsigned > idx_range, Instruction *InsertBefore=nullptr)
FindInsertedValue - Given an aggregrate and an sequence of indices, see if the scalar value indexed i...
SelectPatternFlavor
Specific patterns of select instructions we can match.
unsigned ComputeNumSignBits(Value *Op, const DataLayout &DL, unsigned Depth=0, AssumptionCache *AC=nullptr, const Instruction *CxtI=nullptr, const DominatorTree *DT=nullptr)
ComputeNumSignBits - Return the number of times the sign bit of the register is replicated into the o...
bool isKnownNonNullAt(const Value *V, const Instruction *CtxI=nullptr, const DominatorTree *DT=nullptr, const TargetLibraryInfo *TLI=nullptr)
isKnownNonNullAt - Return true if this pointer couldn't possibly be null.
bool isKnownNonNull(const Value *V, const TargetLibraryInfo *TLI=nullptr)
isKnownNonNull - Return true if this pointer couldn't possibly be null by its definition.
SI Fix SGPR Live Ranges
bool isKnownNonZero(Value *V, const DataLayout &DL, unsigned Depth=0, AssumptionCache *AC=nullptr, const Instruction *CxtI=nullptr, const DominatorTree *DT=nullptr)
isKnownNonZero - Return true if the given value is known to be non-zero when defined.
bool CannotBeOrderedLessThanZero(const Value *V, unsigned Depth=0)
CannotBeOrderedLessThanZero - Return true if we can prove that the specified FP value is either a NaN...
OverflowResult
#define I(x, y, z)
Definition: MD5.cpp:54
bool ComputeMultiple(Value *V, unsigned Base, Value *&Multiple, bool LookThroughSExt=false, unsigned Depth=0)
ComputeMultiple - This function computes the integer multiple of Base that equals V...
bool getConstantStringInfo(const Value *V, StringRef &Str, uint64_t Offset=0, bool TrimAtNul=true)
getConstantStringInfo - This function computes the length of a null-terminated C string pointed to by...
bool CannotBeNegativeZero(const Value *V, unsigned Depth=0)
CannotBeNegativeZero - Return true if we can prove that the specified FP value is never equal to -0...
LLVM Value Representation.
Definition: Value.h:69
bool isSafeToSpeculativelyExecute(const Value *V, const Instruction *CtxI=nullptr, const DominatorTree *DT=nullptr, const TargetLibraryInfo *TLI=nullptr)
isSafeToSpeculativelyExecute - Return true if the instruction does not have any effects besides calcu...