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/IR/Instruction.h"
20 #include "llvm/Support/DataTypes.h"
29 class AssumptionCache;
31 class TargetLibraryInfo;
34 /// Determine which bits of V are known to be either zero or one and return
35 /// them in the KnownZero/KnownOne bit sets.
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,
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);
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);
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);
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);
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.
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);
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.
105 /// 'Op' must have a scalar integer type.
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);
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,
121 /// CannotBeNegativeZero - Return true if we can prove that the specified FP
122 /// value is never equal to -0.0.
124 bool CannotBeNegativeZero(const Value *V, unsigned Depth = 0);
126 /// CannotBeOrderedLessThanZero - Return true if we can prove that the
127 /// specified FP value is either a NaN or never less than 0.0.
129 bool CannotBeOrderedLessThanZero(const Value *V, unsigned Depth = 0);
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);
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.
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);
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,
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);
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);
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);
186 /// \brief This method is similar to GetUnderlyingObject except that it can
187 /// look through phi and select instructions and return multiple objects.
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:
196 /// A[i][j] = A[i-1][j] * B[j]
199 /// This is transformed by Load-PRE to stash away A[i] for the next iteration
200 /// of the outer loop:
202 /// Curr = A[0]; // Prev_0
204 /// Prev = Curr; // Prev = PHI (Prev_0, Curr)
207 /// Curr[j] = Prev[j] * B[j]
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);
218 /// onlyUsedByLifetimeMarkers - Return true if the only users of this pointer
219 /// are lifetime markers.
220 bool onlyUsedByLifetimeMarkers(const Value *V);
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);
231 /// isSafeToSpeculativelyExecute - Return true if the instruction does not
232 /// have any effects besides calculating the result and does not have
233 /// undefined behavior.
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.
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
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.
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);
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);
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
269 bool isKnownNonNullAt(const Value *V,
270 const Instruction *CtxI = nullptr,
271 const DominatorTree *DT = nullptr,
272 const TargetLibraryInfo *TLI = nullptr);
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);
280 enum class OverflowResult { AlwaysOverflows, MayOverflow, NeverOverflows };
281 OverflowResult computeOverflowForUnsignedMul(Value *LHS, Value *RHS,
282 const DataLayout &DL,
284 const Instruction *CxtI,
285 const DominatorTree *DT);
286 OverflowResult computeOverflowForUnsignedAdd(Value *LHS, Value *RHS,
287 const DataLayout &DL,
289 const Instruction *CxtI,
290 const DominatorTree *DT);
292 /// \brief Specific patterns of select instructions we can match.
293 enum SelectPatternFlavor {
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
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.
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.
311 /// %1 = icmp slt i32 %a, i32 4
312 /// %2 = sext i32 %a to i64
313 /// %3 = select i1 %1, i64 %2, i64 4
315 /// -> LHS = %a, RHS = i32 4, *CastOp = Instruction::SExt
317 SelectPatternFlavor matchSelectPattern(Value *V, Value *&LHS, Value *&RHS,
318 Instruction::CastOps *CastOp = nullptr);
320 } // end namespace llvm