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/IR/CallSite.h"
19 #include "llvm/IR/Instruction.h"
20 #include "llvm/IR/IntrinsicInst.h"
21 #include "llvm/Support/DataTypes.h"
24 template <typename T> class ArrayRef;
27 class AssumptionCache;
36 class TargetLibraryInfo;
43 /// Determine which bits of V are known to be either zero or one and return
44 /// them in the KnownZero/KnownOne bit sets.
46 /// This function is defined on values with integer type, values with pointer
47 /// type, and vectors of integers. In the case
48 /// where V is a vector, the known zero and known one values are the
49 /// same width as the vector element, and the bit is set only if it is true
50 /// for all of the elements in the vector.
51 void computeKnownBits(const Value *V, APInt &KnownZero, APInt &KnownOne,
52 const DataLayout &DL, unsigned Depth = 0,
53 AssumptionCache *AC = nullptr,
54 const Instruction *CxtI = nullptr,
55 const DominatorTree *DT = nullptr);
56 /// Compute known bits from the range metadata.
57 /// \p KnownZero the set of bits that are known to be zero
58 /// \p KnownOne the set of bits that are known to be one
59 void computeKnownBitsFromRangeMetadata(const MDNode &Ranges,
60 APInt &KnownZero, APInt &KnownOne);
61 /// Return true if LHS and RHS have no common bits set.
62 bool haveNoCommonBitsSet(const Value *LHS, const Value *RHS,
64 AssumptionCache *AC = nullptr,
65 const Instruction *CxtI = nullptr,
66 const DominatorTree *DT = nullptr);
68 /// Determine whether the sign bit is known to be zero or one. Convenience
69 /// wrapper around computeKnownBits.
70 void ComputeSignBit(const Value *V, bool &KnownZero, bool &KnownOne,
71 const DataLayout &DL, unsigned Depth = 0,
72 AssumptionCache *AC = nullptr,
73 const Instruction *CxtI = nullptr,
74 const DominatorTree *DT = nullptr);
76 /// Return true if the given value is known to have exactly one bit set when
77 /// defined. For vectors return true if every element is known to be a power
78 /// of two when defined. Supports values with integer or pointer type and
79 /// vectors of integers. If 'OrZero' is set, then return true if the given
80 /// value is either a power of two or zero.
81 bool isKnownToBeAPowerOfTwo(const Value *V, const DataLayout &DL,
82 bool OrZero = false, unsigned Depth = 0,
83 AssumptionCache *AC = nullptr,
84 const Instruction *CxtI = nullptr,
85 const DominatorTree *DT = nullptr);
87 /// Return true if the given value is known to be non-zero when defined. For
88 /// vectors, return true if every element is known to be non-zero when
89 /// defined. Supports values with integer or pointer type and vectors of
91 bool isKnownNonZero(const Value *V, const DataLayout &DL, unsigned Depth = 0,
92 AssumptionCache *AC = nullptr,
93 const Instruction *CxtI = nullptr,
94 const DominatorTree *DT = nullptr);
96 /// Returns true if the give value is known to be non-negative.
97 bool isKnownNonNegative(const Value *V, const DataLayout &DL,
99 AssumptionCache *AC = nullptr,
100 const Instruction *CxtI = nullptr,
101 const DominatorTree *DT = nullptr);
103 /// Returns true if the given value is known be positive (i.e. non-negative
105 bool isKnownPositive(const Value *V, const DataLayout &DL, unsigned Depth = 0,
106 AssumptionCache *AC = nullptr,
107 const Instruction *CxtI = nullptr,
108 const DominatorTree *DT = nullptr);
110 /// Returns true if the given value is known be negative (i.e. non-positive
112 bool isKnownNegative(const Value *V, const DataLayout &DL, unsigned Depth = 0,
113 AssumptionCache *AC = nullptr,
114 const Instruction *CxtI = nullptr,
115 const DominatorTree *DT = nullptr);
117 /// Return true if the given values are known to be non-equal when defined.
118 /// Supports scalar integer types only.
119 bool isKnownNonEqual(const Value *V1, const Value *V2, const DataLayout &DL,
120 AssumptionCache *AC = nullptr,
121 const Instruction *CxtI = nullptr,
122 const DominatorTree *DT = nullptr);
124 /// Return true if 'V & Mask' is known to be zero. We use this predicate to
125 /// simplify operations downstream. Mask is known to be zero for bits that V
128 /// This function is defined on values with integer type, values with pointer
129 /// type, and vectors of integers. In the case
130 /// where V is a vector, the mask, known zero, and known one values are the
131 /// same width as the vector element, and the bit is set only if it is true
132 /// for all of the elements in the vector.
133 bool MaskedValueIsZero(const Value *V, const APInt &Mask,
134 const DataLayout &DL,
135 unsigned Depth = 0, AssumptionCache *AC = nullptr,
136 const Instruction *CxtI = nullptr,
137 const DominatorTree *DT = nullptr);
139 /// Return the number of times the sign bit of the register is replicated into
140 /// the other bits. We know that at least 1 bit is always equal to the sign
141 /// bit (itself), but other cases can give us information. For example,
142 /// immediately after an "ashr X, 2", we know that the top 3 bits are all
143 /// equal to each other, so we return 3. For vectors, return the number of
144 /// sign bits for the vector element with the mininum number of known sign
146 unsigned ComputeNumSignBits(const Value *Op, const DataLayout &DL,
147 unsigned Depth = 0, AssumptionCache *AC = nullptr,
148 const Instruction *CxtI = nullptr,
149 const DominatorTree *DT = nullptr);
151 /// This function computes the integer multiple of Base that equals V. If
152 /// successful, it returns true and returns the multiple in Multiple. If
153 /// unsuccessful, it returns false. Also, if V can be simplified to an
154 /// integer, then the simplified V is returned in Val. Look through sext only
155 /// if LookThroughSExt=true.
156 bool ComputeMultiple(Value *V, unsigned Base, Value *&Multiple,
157 bool LookThroughSExt = false,
160 /// Map a call instruction to an intrinsic ID. Libcalls which have equivalent
161 /// intrinsics are treated as-if they were intrinsics.
162 Intrinsic::ID getIntrinsicForCallSite(ImmutableCallSite ICS,
163 const TargetLibraryInfo *TLI);
165 /// Return true if we can prove that the specified FP value is never equal to
167 bool CannotBeNegativeZero(const Value *V, const TargetLibraryInfo *TLI,
170 /// Return true if we can prove that the specified FP value is either a NaN or
171 /// never less than 0.0.
172 /// If \p IncludeNeg0 is false, -0.0 is considered less than 0.0.
173 bool CannotBeOrderedLessThanZero(const Value *V, const TargetLibraryInfo *TLI);
175 /// \returns true if we can prove that the specified FP value has a 0 sign
177 bool SignBitMustBeZero(const Value *V, const TargetLibraryInfo *TLI);
179 /// If the specified value can be set by repeating the same byte in memory,
180 /// return the i8 value that it is represented with. This is true for all i8
181 /// values obviously, but is also true for i32 0, i32 -1, i16 0xF0F0, double
182 /// 0.0 etc. If the value can't be handled with a repeated byte store (e.g.
183 /// i16 0x1234), return null.
184 Value *isBytewiseValue(Value *V);
186 /// Given an aggregrate and an sequence of indices, see if the scalar value
187 /// indexed is already around as a register, for example if it were inserted
188 /// directly into the aggregrate.
190 /// If InsertBefore is not null, this function will duplicate (modified)
191 /// insertvalues when a part of a nested struct is extracted.
192 Value *FindInsertedValue(Value *V,
193 ArrayRef<unsigned> idx_range,
194 Instruction *InsertBefore = nullptr);
196 /// Analyze the specified pointer to see if it can be expressed as a base
197 /// pointer plus a constant offset. Return the base and offset to the caller.
198 Value *GetPointerBaseWithConstantOffset(Value *Ptr, int64_t &Offset,
199 const DataLayout &DL);
200 static inline const Value *
201 GetPointerBaseWithConstantOffset(const Value *Ptr, int64_t &Offset,
202 const DataLayout &DL) {
203 return GetPointerBaseWithConstantOffset(const_cast<Value *>(Ptr), Offset,
207 /// Returns true if the GEP is based on a pointer to a string (array of i8),
208 /// and is indexing into this string.
209 bool isGEPBasedOnPointerToString(const GEPOperator *GEP);
211 /// This function computes the length of a null-terminated C string pointed to
212 /// by V. If successful, it returns true and returns the string in Str. If
213 /// unsuccessful, it returns false. This does not include the trailing null
214 /// character by default. If TrimAtNul is set to false, then this returns any
215 /// trailing null characters as well as any other characters that come after
217 bool getConstantStringInfo(const Value *V, StringRef &Str,
218 uint64_t Offset = 0, bool TrimAtNul = true);
220 /// If we can compute the length of the string pointed to by the specified
221 /// pointer, return 'len+1'. If we can't, return 0.
222 uint64_t GetStringLength(const Value *V);
224 /// This method strips off any GEP address adjustments and pointer casts from
225 /// the specified value, returning the original object being addressed. Note
226 /// that the returned value has pointer type if the specified value does. If
227 /// the MaxLookup value is non-zero, it limits the number of instructions to
229 Value *GetUnderlyingObject(Value *V, const DataLayout &DL,
230 unsigned MaxLookup = 6);
231 static inline const Value *GetUnderlyingObject(const Value *V,
232 const DataLayout &DL,
233 unsigned MaxLookup = 6) {
234 return GetUnderlyingObject(const_cast<Value *>(V), DL, MaxLookup);
237 /// \brief This method is similar to GetUnderlyingObject except that it can
238 /// look through phi and select instructions and return multiple objects.
240 /// If LoopInfo is passed, loop phis are further analyzed. If a pointer
241 /// accesses different objects in each iteration, we don't look through the
242 /// phi node. E.g. consider this loop nest:
247 /// A[i][j] = A[i-1][j] * B[j]
250 /// This is transformed by Load-PRE to stash away A[i] for the next iteration
251 /// of the outer loop:
253 /// Curr = A[0]; // Prev_0
255 /// Prev = Curr; // Prev = PHI (Prev_0, Curr)
258 /// Curr[j] = Prev[j] * B[j]
262 /// Since A[i] and A[i-1] are independent pointers, getUnderlyingObjects
263 /// should not assume that Curr and Prev share the same underlying object thus
264 /// it shouldn't look through the phi above.
265 void GetUnderlyingObjects(Value *V, SmallVectorImpl<Value *> &Objects,
266 const DataLayout &DL, LoopInfo *LI = nullptr,
267 unsigned MaxLookup = 6);
269 /// Return true if the only users of this pointer are lifetime markers.
270 bool onlyUsedByLifetimeMarkers(const Value *V);
272 /// Return true if the instruction does not have any effects besides
273 /// calculating the result and does not have undefined behavior.
275 /// This method never returns true for an instruction that returns true for
276 /// mayHaveSideEffects; however, this method also does some other checks in
277 /// addition. It checks for undefined behavior, like dividing by zero or
278 /// loading from an invalid pointer (but not for undefined results, like a
279 /// shift with a shift amount larger than the width of the result). It checks
280 /// for malloc and alloca because speculatively executing them might cause a
281 /// memory leak. It also returns false for instructions related to control
282 /// flow, specifically terminators and PHI nodes.
284 /// If the CtxI is specified this method performs context-sensitive analysis
285 /// and returns true if it is safe to execute the instruction immediately
288 /// If the CtxI is NOT specified this method only looks at the instruction
289 /// itself and its operands, so if this method returns true, it is safe to
290 /// move the instruction as long as the correct dominance relationships for
291 /// the operands and users hold.
293 /// This method can return true for instructions that read memory;
294 /// for such instructions, moving them may change the resulting value.
295 bool isSafeToSpeculativelyExecute(const Value *V,
296 const Instruction *CtxI = nullptr,
297 const DominatorTree *DT = nullptr);
299 /// Returns true if the result or effects of the given instructions \p I
300 /// depend on or influence global memory.
301 /// Memory dependence arises for example if the instruction reads from
302 /// memory or may produce effects or undefined behaviour. Memory dependent
303 /// instructions generally cannot be reorderd with respect to other memory
304 /// dependent instructions or moved into non-dominated basic blocks.
305 /// Instructions which just compute a value based on the values of their
306 /// operands are not memory dependent.
307 bool mayBeMemoryDependent(const Instruction &I);
309 /// Return true if this pointer couldn't possibly be null by its definition.
310 /// This returns true for allocas, non-extern-weak globals, and byval
312 bool isKnownNonNull(const Value *V);
314 /// Return true if this pointer couldn't possibly be null. If the context
315 /// instruction and dominator tree are specified, perform context-sensitive
316 /// analysis and return true if the pointer couldn't possibly be null at the
317 /// specified instruction.
318 bool isKnownNonNullAt(const Value *V,
319 const Instruction *CtxI = nullptr,
320 const DominatorTree *DT = nullptr);
322 /// Return true if it is valid to use the assumptions provided by an
323 /// assume intrinsic, I, at the point in the control-flow identified by the
324 /// context instruction, CxtI.
325 bool isValidAssumeForContext(const Instruction *I, const Instruction *CxtI,
326 const DominatorTree *DT = nullptr);
328 enum class OverflowResult { AlwaysOverflows, MayOverflow, NeverOverflows };
329 OverflowResult computeOverflowForUnsignedMul(const Value *LHS,
331 const DataLayout &DL,
333 const Instruction *CxtI,
334 const DominatorTree *DT);
335 OverflowResult computeOverflowForUnsignedAdd(const Value *LHS,
337 const DataLayout &DL,
339 const Instruction *CxtI,
340 const DominatorTree *DT);
341 OverflowResult computeOverflowForSignedAdd(const Value *LHS, const Value *RHS,
342 const DataLayout &DL,
343 AssumptionCache *AC = nullptr,
344 const Instruction *CxtI = nullptr,
345 const DominatorTree *DT = nullptr);
346 /// This version also leverages the sign bit of Add if known.
347 OverflowResult computeOverflowForSignedAdd(const AddOperator *Add,
348 const DataLayout &DL,
349 AssumptionCache *AC = nullptr,
350 const Instruction *CxtI = nullptr,
351 const DominatorTree *DT = nullptr);
353 /// Returns true if the arithmetic part of the \p II 's result is
354 /// used only along the paths control dependent on the computation
355 /// not overflowing, \p II being an <op>.with.overflow intrinsic.
356 bool isOverflowIntrinsicNoWrap(const IntrinsicInst *II,
357 const DominatorTree &DT);
359 /// Return true if this function can prove that the instruction I will
360 /// always transfer execution to one of its successors (including the next
361 /// instruction that follows within a basic block). E.g. this is not
362 /// guaranteed for function calls that could loop infinitely.
364 /// In other words, this function returns false for instructions that may
365 /// transfer execution or fail to transfer execution in a way that is not
366 /// captured in the CFG nor in the sequence of instructions within a basic
369 /// Undefined behavior is assumed not to happen, so e.g. division is
370 /// guaranteed to transfer execution to the following instruction even
371 /// though division by zero might cause undefined behavior.
372 bool isGuaranteedToTransferExecutionToSuccessor(const Instruction *I);
374 /// Return true if this function can prove that the instruction I
375 /// is executed for every iteration of the loop L.
377 /// Note that this currently only considers the loop header.
378 bool isGuaranteedToExecuteForEveryIteration(const Instruction *I,
381 /// Return true if this function can prove that I is guaranteed to yield
382 /// full-poison (all bits poison) if at least one of its operands are
383 /// full-poison (all bits poison).
385 /// The exact rules for how poison propagates through instructions have
386 /// not been settled as of 2015-07-10, so this function is conservative
387 /// and only considers poison to be propagated in uncontroversial
388 /// cases. There is no attempt to track values that may be only partially
390 bool propagatesFullPoison(const Instruction *I);
392 /// Return either nullptr or an operand of I such that I will trigger
393 /// undefined behavior if I is executed and that operand has a full-poison
394 /// value (all bits poison).
395 const Value *getGuaranteedNonFullPoisonOp(const Instruction *I);
397 /// Return true if this function can prove that if PoisonI is executed
398 /// and yields a full-poison value (all bits poison), then that will
399 /// trigger undefined behavior.
401 /// Note that this currently only considers the basic block that is
403 bool isKnownNotFullPoison(const Instruction *PoisonI);
405 /// \brief Specific patterns of select instructions we can match.
406 enum SelectPatternFlavor {
408 SPF_SMIN, /// Signed minimum
409 SPF_UMIN, /// Unsigned minimum
410 SPF_SMAX, /// Signed maximum
411 SPF_UMAX, /// Unsigned maximum
412 SPF_FMINNUM, /// Floating point minnum
413 SPF_FMAXNUM, /// Floating point maxnum
414 SPF_ABS, /// Absolute value
415 SPF_NABS /// Negated absolute value
417 /// \brief Behavior when a floating point min/max is given one NaN and one
418 /// non-NaN as input.
419 enum SelectPatternNaNBehavior {
420 SPNB_NA = 0, /// NaN behavior not applicable.
421 SPNB_RETURNS_NAN, /// Given one NaN input, returns the NaN.
422 SPNB_RETURNS_OTHER, /// Given one NaN input, returns the non-NaN.
423 SPNB_RETURNS_ANY /// Given one NaN input, can return either (or
424 /// it has been determined that no operands can
427 struct SelectPatternResult {
428 SelectPatternFlavor Flavor;
429 SelectPatternNaNBehavior NaNBehavior; /// Only applicable if Flavor is
430 /// SPF_FMINNUM or SPF_FMAXNUM.
431 bool Ordered; /// When implementing this min/max pattern as
432 /// fcmp; select, does the fcmp have to be
435 /// \brief Return true if \p SPF is a min or a max pattern.
436 static bool isMinOrMax(SelectPatternFlavor SPF) {
437 return !(SPF == SPF_UNKNOWN || SPF == SPF_ABS || SPF == SPF_NABS);
440 /// Pattern match integer [SU]MIN, [SU]MAX and ABS idioms, returning the kind
441 /// and providing the out parameter results if we successfully match.
443 /// If CastOp is not nullptr, also match MIN/MAX idioms where the type does
444 /// not match that of the original select. If this is the case, the cast
445 /// operation (one of Trunc,SExt,Zext) that must be done to transform the
446 /// type of LHS and RHS into the type of V is returned in CastOp.
449 /// %1 = icmp slt i32 %a, i32 4
450 /// %2 = sext i32 %a to i64
451 /// %3 = select i1 %1, i64 %2, i64 4
453 /// -> LHS = %a, RHS = i32 4, *CastOp = Instruction::SExt
455 SelectPatternResult matchSelectPattern(Value *V, Value *&LHS, Value *&RHS,
456 Instruction::CastOps *CastOp = nullptr);
457 static inline SelectPatternResult
458 matchSelectPattern(const Value *V, const Value *&LHS, const Value *&RHS,
459 Instruction::CastOps *CastOp = nullptr) {
460 Value *L = const_cast<Value*>(LHS);
461 Value *R = const_cast<Value*>(RHS);
462 auto Result = matchSelectPattern(const_cast<Value*>(V), L, R);
468 /// Return true if RHS is known to be implied true by LHS. Return false if
469 /// RHS is known to be implied false by LHS. Otherwise, return None if no
470 /// implication can be made.
471 /// A & B must be i1 (boolean) values or a vector of such values. Note that
472 /// the truth table for implication is the same as <=u on i1 values (but not
473 /// <=s!). The truth table for both is:
478 Optional<bool> isImpliedCondition(const Value *LHS, const Value *RHS,
479 const DataLayout &DL,
480 bool InvertAPred = false,
482 AssumptionCache *AC = nullptr,
483 const Instruction *CxtI = nullptr,
484 const DominatorTree *DT = nullptr);
485 } // end namespace llvm