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 bool CannotBeOrderedLessThanZero(const Value *V, const TargetLibraryInfo *TLI,
175 /// If the specified value can be set by repeating the same byte in memory,
176 /// return the i8 value that it is represented with. This is true for all i8
177 /// values obviously, but is also true for i32 0, i32 -1, i16 0xF0F0, double
178 /// 0.0 etc. If the value can't be handled with a repeated byte store (e.g.
179 /// i16 0x1234), return null.
180 Value *isBytewiseValue(Value *V);
182 /// Given an aggregrate and an sequence of indices, see if the scalar value
183 /// indexed is already around as a register, for example if it were inserted
184 /// directly into the aggregrate.
186 /// If InsertBefore is not null, this function will duplicate (modified)
187 /// insertvalues when a part of a nested struct is extracted.
188 Value *FindInsertedValue(Value *V,
189 ArrayRef<unsigned> idx_range,
190 Instruction *InsertBefore = nullptr);
192 /// Analyze the specified pointer to see if it can be expressed as a base
193 /// pointer plus a constant offset. Return the base and offset to the caller.
194 Value *GetPointerBaseWithConstantOffset(Value *Ptr, int64_t &Offset,
195 const DataLayout &DL);
196 static inline const Value *
197 GetPointerBaseWithConstantOffset(const Value *Ptr, int64_t &Offset,
198 const DataLayout &DL) {
199 return GetPointerBaseWithConstantOffset(const_cast<Value *>(Ptr), Offset,
203 /// Returns true if the GEP is based on a pointer to a string (array of i8),
204 /// and is indexing into this string.
205 bool isGEPBasedOnPointerToString(const GEPOperator *GEP);
207 /// This function computes the length of a null-terminated C string pointed to
208 /// by V. If successful, it returns true and returns the string in Str. If
209 /// unsuccessful, it returns false. This does not include the trailing null
210 /// character by default. If TrimAtNul is set to false, then this returns any
211 /// trailing null characters as well as any other characters that come after
213 bool getConstantStringInfo(const Value *V, StringRef &Str,
214 uint64_t Offset = 0, bool TrimAtNul = true);
216 /// If we can compute the length of the string pointed to by the specified
217 /// pointer, return 'len+1'. If we can't, return 0.
218 uint64_t GetStringLength(const Value *V);
220 /// This method strips off any GEP address adjustments and pointer casts from
221 /// the specified value, returning the original object being addressed. Note
222 /// that the returned value has pointer type if the specified value does. If
223 /// the MaxLookup value is non-zero, it limits the number of instructions to
225 Value *GetUnderlyingObject(Value *V, const DataLayout &DL,
226 unsigned MaxLookup = 6);
227 static inline const Value *GetUnderlyingObject(const Value *V,
228 const DataLayout &DL,
229 unsigned MaxLookup = 6) {
230 return GetUnderlyingObject(const_cast<Value *>(V), DL, MaxLookup);
233 /// \brief This method is similar to GetUnderlyingObject except that it can
234 /// look through phi and select instructions and return multiple objects.
236 /// If LoopInfo is passed, loop phis are further analyzed. If a pointer
237 /// accesses different objects in each iteration, we don't look through the
238 /// phi node. E.g. consider this loop nest:
243 /// A[i][j] = A[i-1][j] * B[j]
246 /// This is transformed by Load-PRE to stash away A[i] for the next iteration
247 /// of the outer loop:
249 /// Curr = A[0]; // Prev_0
251 /// Prev = Curr; // Prev = PHI (Prev_0, Curr)
254 /// Curr[j] = Prev[j] * B[j]
258 /// Since A[i] and A[i-1] are independent pointers, getUnderlyingObjects
259 /// should not assume that Curr and Prev share the same underlying object thus
260 /// it shouldn't look through the phi above.
261 void GetUnderlyingObjects(Value *V, SmallVectorImpl<Value *> &Objects,
262 const DataLayout &DL, LoopInfo *LI = nullptr,
263 unsigned MaxLookup = 6);
265 /// Return true if the only users of this pointer are lifetime markers.
266 bool onlyUsedByLifetimeMarkers(const Value *V);
268 /// Return true if the instruction does not have any effects besides
269 /// calculating the result and does not have undefined behavior.
271 /// This method never returns true for an instruction that returns true for
272 /// mayHaveSideEffects; however, this method also does some other checks in
273 /// addition. It checks for undefined behavior, like dividing by zero or
274 /// loading from an invalid pointer (but not for undefined results, like a
275 /// shift with a shift amount larger than the width of the result). It checks
276 /// for malloc and alloca because speculatively executing them might cause a
277 /// memory leak. It also returns false for instructions related to control
278 /// flow, specifically terminators and PHI nodes.
280 /// If the CtxI is specified this method performs context-sensitive analysis
281 /// and returns true if it is safe to execute the instruction immediately
284 /// If the CtxI is NOT specified this method only looks at the instruction
285 /// itself and its operands, so if this method returns true, it is safe to
286 /// move the instruction as long as the correct dominance relationships for
287 /// the operands and users hold.
289 /// This method can return true for instructions that read memory;
290 /// for such instructions, moving them may change the resulting value.
291 bool isSafeToSpeculativelyExecute(const Value *V,
292 const Instruction *CtxI = nullptr,
293 const DominatorTree *DT = nullptr);
295 /// Returns true if the result or effects of the given instructions \p I
296 /// depend on or influence global memory.
297 /// Memory dependence arises for example if the instruction reads from
298 /// memory or may produce effects or undefined behaviour. Memory dependent
299 /// instructions generally cannot be reorderd with respect to other memory
300 /// dependent instructions or moved into non-dominated basic blocks.
301 /// Instructions which just compute a value based on the values of their
302 /// operands are not memory dependent.
303 bool mayBeMemoryDependent(const Instruction &I);
305 /// Return true if this pointer couldn't possibly be null by its definition.
306 /// This returns true for allocas, non-extern-weak globals, and byval
308 bool isKnownNonNull(const Value *V);
310 /// Return true if this pointer couldn't possibly be null. If the context
311 /// instruction and dominator tree are specified, perform context-sensitive
312 /// analysis and return true if the pointer couldn't possibly be null at the
313 /// specified instruction.
314 bool isKnownNonNullAt(const Value *V,
315 const Instruction *CtxI = nullptr,
316 const DominatorTree *DT = nullptr);
318 /// Return true if it is valid to use the assumptions provided by an
319 /// assume intrinsic, I, at the point in the control-flow identified by the
320 /// context instruction, CxtI.
321 bool isValidAssumeForContext(const Instruction *I, const Instruction *CxtI,
322 const DominatorTree *DT = nullptr);
324 enum class OverflowResult { AlwaysOverflows, MayOverflow, NeverOverflows };
325 OverflowResult computeOverflowForUnsignedMul(const Value *LHS,
327 const DataLayout &DL,
329 const Instruction *CxtI,
330 const DominatorTree *DT);
331 OverflowResult computeOverflowForUnsignedAdd(const Value *LHS,
333 const DataLayout &DL,
335 const Instruction *CxtI,
336 const DominatorTree *DT);
337 OverflowResult computeOverflowForSignedAdd(const Value *LHS, const Value *RHS,
338 const DataLayout &DL,
339 AssumptionCache *AC = nullptr,
340 const Instruction *CxtI = nullptr,
341 const DominatorTree *DT = nullptr);
342 /// This version also leverages the sign bit of Add if known.
343 OverflowResult computeOverflowForSignedAdd(const AddOperator *Add,
344 const DataLayout &DL,
345 AssumptionCache *AC = nullptr,
346 const Instruction *CxtI = nullptr,
347 const DominatorTree *DT = nullptr);
349 /// Returns true if the arithmetic part of the \p II 's result is
350 /// used only along the paths control dependent on the computation
351 /// not overflowing, \p II being an <op>.with.overflow intrinsic.
352 bool isOverflowIntrinsicNoWrap(const IntrinsicInst *II,
353 const DominatorTree &DT);
355 /// Return true if this function can prove that the instruction I will
356 /// always transfer execution to one of its successors (including the next
357 /// instruction that follows within a basic block). E.g. this is not
358 /// guaranteed for function calls that could loop infinitely.
360 /// In other words, this function returns false for instructions that may
361 /// transfer execution or fail to transfer execution in a way that is not
362 /// captured in the CFG nor in the sequence of instructions within a basic
365 /// Undefined behavior is assumed not to happen, so e.g. division is
366 /// guaranteed to transfer execution to the following instruction even
367 /// though division by zero might cause undefined behavior.
368 bool isGuaranteedToTransferExecutionToSuccessor(const Instruction *I);
370 /// Return true if this function can prove that the instruction I
371 /// is executed for every iteration of the loop L.
373 /// Note that this currently only considers the loop header.
374 bool isGuaranteedToExecuteForEveryIteration(const Instruction *I,
377 /// Return true if this function can prove that I is guaranteed to yield
378 /// full-poison (all bits poison) if at least one of its operands are
379 /// full-poison (all bits poison).
381 /// The exact rules for how poison propagates through instructions have
382 /// not been settled as of 2015-07-10, so this function is conservative
383 /// and only considers poison to be propagated in uncontroversial
384 /// cases. There is no attempt to track values that may be only partially
386 bool propagatesFullPoison(const Instruction *I);
388 /// Return either nullptr or an operand of I such that I will trigger
389 /// undefined behavior if I is executed and that operand has a full-poison
390 /// value (all bits poison).
391 const Value *getGuaranteedNonFullPoisonOp(const Instruction *I);
393 /// Return true if this function can prove that if PoisonI is executed
394 /// and yields a full-poison value (all bits poison), then that will
395 /// trigger undefined behavior.
397 /// Note that this currently only considers the basic block that is
399 bool isKnownNotFullPoison(const Instruction *PoisonI);
401 /// \brief Specific patterns of select instructions we can match.
402 enum SelectPatternFlavor {
404 SPF_SMIN, /// Signed minimum
405 SPF_UMIN, /// Unsigned minimum
406 SPF_SMAX, /// Signed maximum
407 SPF_UMAX, /// Unsigned maximum
408 SPF_FMINNUM, /// Floating point minnum
409 SPF_FMAXNUM, /// Floating point maxnum
410 SPF_ABS, /// Absolute value
411 SPF_NABS /// Negated absolute value
413 /// \brief Behavior when a floating point min/max is given one NaN and one
414 /// non-NaN as input.
415 enum SelectPatternNaNBehavior {
416 SPNB_NA = 0, /// NaN behavior not applicable.
417 SPNB_RETURNS_NAN, /// Given one NaN input, returns the NaN.
418 SPNB_RETURNS_OTHER, /// Given one NaN input, returns the non-NaN.
419 SPNB_RETURNS_ANY /// Given one NaN input, can return either (or
420 /// it has been determined that no operands can
423 struct SelectPatternResult {
424 SelectPatternFlavor Flavor;
425 SelectPatternNaNBehavior NaNBehavior; /// Only applicable if Flavor is
426 /// SPF_FMINNUM or SPF_FMAXNUM.
427 bool Ordered; /// When implementing this min/max pattern as
428 /// fcmp; select, does the fcmp have to be
431 /// \brief Return true if \p SPF is a min or a max pattern.
432 static bool isMinOrMax(SelectPatternFlavor SPF) {
433 return !(SPF == SPF_UNKNOWN || SPF == SPF_ABS || SPF == SPF_NABS);
436 /// Pattern match integer [SU]MIN, [SU]MAX and ABS idioms, returning the kind
437 /// and providing the out parameter results if we successfully match.
439 /// If CastOp is not nullptr, also match MIN/MAX idioms where the type does
440 /// not match that of the original select. If this is the case, the cast
441 /// operation (one of Trunc,SExt,Zext) that must be done to transform the
442 /// type of LHS and RHS into the type of V is returned in CastOp.
445 /// %1 = icmp slt i32 %a, i32 4
446 /// %2 = sext i32 %a to i64
447 /// %3 = select i1 %1, i64 %2, i64 4
449 /// -> LHS = %a, RHS = i32 4, *CastOp = Instruction::SExt
451 SelectPatternResult matchSelectPattern(Value *V, Value *&LHS, Value *&RHS,
452 Instruction::CastOps *CastOp = nullptr);
453 static inline SelectPatternResult
454 matchSelectPattern(const Value *V, const Value *&LHS, const Value *&RHS,
455 Instruction::CastOps *CastOp = nullptr) {
456 Value *L = const_cast<Value*>(LHS);
457 Value *R = const_cast<Value*>(RHS);
458 auto Result = matchSelectPattern(const_cast<Value*>(V), L, R);
464 /// Return true if RHS is known to be implied true by LHS. Return false if
465 /// RHS is known to be implied false by LHS. Otherwise, return None if no
466 /// implication can be made.
467 /// A & B must be i1 (boolean) values or a vector of such values. Note that
468 /// the truth table for implication is the same as <=u on i1 values (but not
469 /// <=s!). The truth table for both is:
474 Optional<bool> isImpliedCondition(const Value *LHS, const Value *RHS,
475 const DataLayout &DL,
476 bool InvertAPred = false,
478 AssumptionCache *AC = nullptr,
479 const Instruction *CxtI = nullptr,
480 const DominatorTree *DT = nullptr);
481 } // end namespace llvm