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/ConstantRange.h"
20 #include "llvm/IR/Instruction.h"
21 #include "llvm/IR/IntrinsicInst.h"
22 #include "llvm/Support/DataTypes.h"
25 template <typename T> class ArrayRef;
28 class AssumptionCache;
37 class TargetLibraryInfo;
44 /// Determine which bits of V are known to be either zero or one and return
45 /// them in the KnownZero/KnownOne bit sets.
47 /// This function is defined on values with integer type, values with pointer
48 /// type, and vectors of integers. In the case
49 /// where V is a vector, the known zero and known one values are the
50 /// same width as the vector element, and the bit is set only if it is true
51 /// for all of the elements in the vector.
52 void computeKnownBits(Value *V, APInt &KnownZero, APInt &KnownOne,
53 const DataLayout &DL, unsigned Depth = 0,
54 AssumptionCache *AC = nullptr,
55 const Instruction *CxtI = nullptr,
56 const DominatorTree *DT = nullptr);
57 /// Compute known bits from the range metadata.
58 /// \p KnownZero the set of bits that are known to be zero
59 /// \p KnownOne the set of bits that are known to be one
60 void computeKnownBitsFromRangeMetadata(const MDNode &Ranges,
61 APInt &KnownZero, APInt &KnownOne);
62 /// Return true if LHS and RHS have no common bits set.
63 bool haveNoCommonBitsSet(Value *LHS, Value *RHS, const DataLayout &DL,
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(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(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(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(Value *V, const DataLayout &DL, unsigned Depth = 0,
98 AssumptionCache *AC = nullptr,
99 const Instruction *CxtI = nullptr,
100 const DominatorTree *DT = nullptr);
102 /// Returns true if the given value is known be positive (i.e. non-negative
104 bool isKnownPositive(Value *V, const DataLayout &DL, unsigned Depth = 0,
105 AssumptionCache *AC = nullptr,
106 const Instruction *CxtI = nullptr,
107 const DominatorTree *DT = nullptr);
109 /// Returns true if the given value is known be negative (i.e. non-positive
111 bool isKnownNegative(Value *V, const DataLayout &DL, unsigned Depth = 0,
112 AssumptionCache *AC = nullptr,
113 const Instruction *CxtI = nullptr,
114 const DominatorTree *DT = nullptr);
116 /// Return true if the given values are known to be non-equal when defined.
117 /// Supports scalar integer types only.
118 bool isKnownNonEqual(Value *V1, Value *V2, const DataLayout &DL,
119 AssumptionCache *AC = nullptr,
120 const Instruction *CxtI = nullptr,
121 const DominatorTree *DT = nullptr);
123 /// Return true if 'V & Mask' is known to be zero. We use this predicate to
124 /// simplify operations downstream. Mask is known to be zero for bits that V
127 /// This function is defined on values with integer type, values with pointer
128 /// type, and vectors of integers. In the case
129 /// where V is a vector, the mask, known zero, and known one values are the
130 /// same width as the vector element, and the bit is set only if it is true
131 /// for all of the elements in the vector.
132 bool MaskedValueIsZero(Value *V, const APInt &Mask, const DataLayout &DL,
133 unsigned Depth = 0, AssumptionCache *AC = nullptr,
134 const Instruction *CxtI = nullptr,
135 const DominatorTree *DT = nullptr);
137 /// Return the number of times the sign bit of the register is replicated into
138 /// the other bits. We know that at least 1 bit is always equal to the sign
139 /// bit (itself), but other cases can give us information. For example,
140 /// immediately after an "ashr X, 2", we know that the top 3 bits are all
141 /// equal to each other, so we return 3. For vectors, return the number of
142 /// sign bits for the vector element with the mininum number of known sign
144 unsigned ComputeNumSignBits(Value *Op, const DataLayout &DL,
145 unsigned Depth = 0, AssumptionCache *AC = nullptr,
146 const Instruction *CxtI = nullptr,
147 const DominatorTree *DT = nullptr);
149 /// This function computes the integer multiple of Base that equals V. If
150 /// successful, it returns true and returns the multiple in Multiple. If
151 /// unsuccessful, it returns false. Also, if V can be simplified to an
152 /// integer, then the simplified V is returned in Val. Look through sext only
153 /// if LookThroughSExt=true.
154 bool ComputeMultiple(Value *V, unsigned Base, Value *&Multiple,
155 bool LookThroughSExt = false,
158 /// Map a call instruction to an intrinsic ID. Libcalls which have equivalent
159 /// intrinsics are treated as-if they were intrinsics.
160 Intrinsic::ID getIntrinsicForCallSite(ImmutableCallSite ICS,
161 const TargetLibraryInfo *TLI);
163 /// Return true if we can prove that the specified FP value is never equal to
165 bool CannotBeNegativeZero(const Value *V, const TargetLibraryInfo *TLI,
168 /// Return true if we can prove that the specified FP value is either a NaN or
169 /// never less than 0.0.
170 bool CannotBeOrderedLessThanZero(const Value *V, const TargetLibraryInfo *TLI,
173 /// If the specified value can be set by repeating the same byte in memory,
174 /// return the i8 value that it is represented with. This is true for all i8
175 /// values obviously, but is also true for i32 0, i32 -1, i16 0xF0F0, double
176 /// 0.0 etc. If the value can't be handled with a repeated byte store (e.g.
177 /// i16 0x1234), return null.
178 Value *isBytewiseValue(Value *V);
180 /// Given an aggregrate and an sequence of indices, see if the scalar value
181 /// indexed is already around as a register, for example if it were inserted
182 /// directly into the aggregrate.
184 /// If InsertBefore is not null, this function will duplicate (modified)
185 /// insertvalues when a part of a nested struct is extracted.
186 Value *FindInsertedValue(Value *V,
187 ArrayRef<unsigned> idx_range,
188 Instruction *InsertBefore = nullptr);
190 /// Analyze the specified pointer to see if it can be expressed as a base
191 /// pointer plus a constant offset. Return the base and offset to the caller.
192 Value *GetPointerBaseWithConstantOffset(Value *Ptr, int64_t &Offset,
193 const DataLayout &DL);
194 static inline const Value *
195 GetPointerBaseWithConstantOffset(const Value *Ptr, int64_t &Offset,
196 const DataLayout &DL) {
197 return GetPointerBaseWithConstantOffset(const_cast<Value *>(Ptr), Offset,
201 /// Returns true if the GEP is based on a pointer to a string (array of i8),
202 /// and is indexing into this string.
203 bool isGEPBasedOnPointerToString(const GEPOperator *GEP);
205 /// This function computes the length of a null-terminated C string pointed to
206 /// by V. If successful, it returns true and returns the string in Str. If
207 /// unsuccessful, it returns false. This does not include the trailing null
208 /// character by default. If TrimAtNul is set to false, then this returns any
209 /// trailing null characters as well as any other characters that come after
211 bool getConstantStringInfo(const Value *V, StringRef &Str,
212 uint64_t Offset = 0, bool TrimAtNul = true);
214 /// If we can compute the length of the string pointed to by the specified
215 /// pointer, return 'len+1'. If we can't, return 0.
216 uint64_t GetStringLength(Value *V);
218 /// This method strips off any GEP address adjustments and pointer casts from
219 /// the specified value, returning the original object being addressed. Note
220 /// that the returned value has pointer type if the specified value does. If
221 /// the MaxLookup value is non-zero, it limits the number of instructions to
223 Value *GetUnderlyingObject(Value *V, const DataLayout &DL,
224 unsigned MaxLookup = 6);
225 static inline const Value *GetUnderlyingObject(const Value *V,
226 const DataLayout &DL,
227 unsigned MaxLookup = 6) {
228 return GetUnderlyingObject(const_cast<Value *>(V), DL, MaxLookup);
231 /// \brief This method is similar to GetUnderlyingObject except that it can
232 /// look through phi and select instructions and return multiple objects.
234 /// If LoopInfo is passed, loop phis are further analyzed. If a pointer
235 /// accesses different objects in each iteration, we don't look through the
236 /// phi node. E.g. consider this loop nest:
241 /// A[i][j] = A[i-1][j] * B[j]
244 /// This is transformed by Load-PRE to stash away A[i] for the next iteration
245 /// of the outer loop:
247 /// Curr = A[0]; // Prev_0
249 /// Prev = Curr; // Prev = PHI (Prev_0, Curr)
252 /// Curr[j] = Prev[j] * B[j]
256 /// Since A[i] and A[i-1] are independent pointers, getUnderlyingObjects
257 /// should not assume that Curr and Prev share the same underlying object thus
258 /// it shouldn't look through the phi above.
259 void GetUnderlyingObjects(Value *V, SmallVectorImpl<Value *> &Objects,
260 const DataLayout &DL, LoopInfo *LI = nullptr,
261 unsigned MaxLookup = 6);
263 /// Return true if the only users of this pointer are lifetime markers.
264 bool onlyUsedByLifetimeMarkers(const Value *V);
266 /// Return true if the instruction does not have any effects besides
267 /// calculating the result and does not have undefined behavior.
269 /// This method never returns true for an instruction that returns true for
270 /// mayHaveSideEffects; however, this method also does some other checks in
271 /// addition. It checks for undefined behavior, like dividing by zero or
272 /// loading from an invalid pointer (but not for undefined results, like a
273 /// shift with a shift amount larger than the width of the result). It checks
274 /// for malloc and alloca because speculatively executing them might cause a
275 /// memory leak. It also returns false for instructions related to control
276 /// flow, specifically terminators and PHI nodes.
278 /// If the CtxI is specified this method performs context-sensitive analysis
279 /// and returns true if it is safe to execute the instruction immediately
282 /// If the CtxI is NOT specified this method only looks at the instruction
283 /// itself and its operands, so if this method returns true, it is safe to
284 /// move the instruction as long as the correct dominance relationships for
285 /// the operands and users hold.
287 /// This method can return true for instructions that read memory;
288 /// for such instructions, moving them may change the resulting value.
289 bool isSafeToSpeculativelyExecute(const Value *V,
290 const Instruction *CtxI = nullptr,
291 const DominatorTree *DT = nullptr);
293 /// Returns true if the result or effects of the given instructions \p I
294 /// depend on or influence global memory.
295 /// Memory dependence arises for example if the instruction reads from
296 /// memory or may produce effects or undefined behaviour. Memory dependent
297 /// instructions generally cannot be reorderd with respect to other memory
298 /// dependent instructions or moved into non-dominated basic blocks.
299 /// Instructions which just compute a value based on the values of their
300 /// operands are not memory dependent.
301 bool mayBeMemoryDependent(const Instruction &I);
303 /// Return true if this pointer couldn't possibly be null by its definition.
304 /// This returns true for allocas, non-extern-weak globals, and byval
306 bool isKnownNonNull(const Value *V);
308 /// Return true if this pointer couldn't possibly be null. If the context
309 /// instruction is specified, perform context-sensitive analysis and return
310 /// true if the pointer couldn't possibly be null at the specified
312 bool isKnownNonNullAt(const Value *V,
313 const Instruction *CtxI = nullptr,
314 const DominatorTree *DT = nullptr);
316 /// Return true if it is valid to use the assumptions provided by an
317 /// assume intrinsic, I, at the point in the control-flow identified by the
318 /// context instruction, CxtI.
319 bool isValidAssumeForContext(const Instruction *I, const Instruction *CxtI,
320 const DominatorTree *DT = nullptr);
322 enum class OverflowResult { AlwaysOverflows, MayOverflow, NeverOverflows };
323 OverflowResult computeOverflowForUnsignedMul(Value *LHS, Value *RHS,
324 const DataLayout &DL,
326 const Instruction *CxtI,
327 const DominatorTree *DT);
328 OverflowResult computeOverflowForUnsignedAdd(Value *LHS, Value *RHS,
329 const DataLayout &DL,
331 const Instruction *CxtI,
332 const DominatorTree *DT);
333 OverflowResult computeOverflowForSignedAdd(Value *LHS, Value *RHS,
334 const DataLayout &DL,
335 AssumptionCache *AC = nullptr,
336 const Instruction *CxtI = nullptr,
337 const DominatorTree *DT = nullptr);
338 /// This version also leverages the sign bit of Add if known.
339 OverflowResult computeOverflowForSignedAdd(AddOperator *Add,
340 const DataLayout &DL,
341 AssumptionCache *AC = nullptr,
342 const Instruction *CxtI = nullptr,
343 const DominatorTree *DT = nullptr);
345 /// Returns true if the arithmetic part of the \p II 's result is
346 /// used only along the paths control dependent on the computation
347 /// not overflowing, \p II being an <op>.with.overflow intrinsic.
348 bool isOverflowIntrinsicNoWrap(IntrinsicInst *II, DominatorTree &DT);
350 /// Return true if this function can prove that the instruction I will
351 /// always transfer execution to one of its successors (including the next
352 /// instruction that follows within a basic block). E.g. this is not
353 /// guaranteed for function calls that could loop infinitely.
355 /// In other words, this function returns false for instructions that may
356 /// transfer execution or fail to transfer execution in a way that is not
357 /// captured in the CFG nor in the sequence of instructions within a basic
360 /// Undefined behavior is assumed not to happen, so e.g. division is
361 /// guaranteed to transfer execution to the following instruction even
362 /// though division by zero might cause undefined behavior.
363 bool isGuaranteedToTransferExecutionToSuccessor(const Instruction *I);
365 /// Return true if this function can prove that the instruction I
366 /// is executed for every iteration of the loop L.
368 /// Note that this currently only considers the loop header.
369 bool isGuaranteedToExecuteForEveryIteration(const Instruction *I,
372 /// Return true if this function can prove that I is guaranteed to yield
373 /// full-poison (all bits poison) if at least one of its operands are
374 /// full-poison (all bits poison).
376 /// The exact rules for how poison propagates through instructions have
377 /// not been settled as of 2015-07-10, so this function is conservative
378 /// and only considers poison to be propagated in uncontroversial
379 /// cases. There is no attempt to track values that may be only partially
381 bool propagatesFullPoison(const Instruction *I);
383 /// Return either nullptr or an operand of I such that I will trigger
384 /// undefined behavior if I is executed and that operand has a full-poison
385 /// value (all bits poison).
386 const Value *getGuaranteedNonFullPoisonOp(const Instruction *I);
388 /// Return true if this function can prove that if PoisonI is executed
389 /// and yields a full-poison value (all bits poison), then that will
390 /// trigger undefined behavior.
392 /// Note that this currently only considers the basic block that is
394 bool isKnownNotFullPoison(const Instruction *PoisonI);
396 /// \brief Specific patterns of select instructions we can match.
397 enum SelectPatternFlavor {
399 SPF_SMIN, /// Signed minimum
400 SPF_UMIN, /// Unsigned minimum
401 SPF_SMAX, /// Signed maximum
402 SPF_UMAX, /// Unsigned maximum
403 SPF_FMINNUM, /// Floating point minnum
404 SPF_FMAXNUM, /// Floating point maxnum
405 SPF_ABS, /// Absolute value
406 SPF_NABS /// Negated absolute value
408 /// \brief Behavior when a floating point min/max is given one NaN and one
409 /// non-NaN as input.
410 enum SelectPatternNaNBehavior {
411 SPNB_NA = 0, /// NaN behavior not applicable.
412 SPNB_RETURNS_NAN, /// Given one NaN input, returns the NaN.
413 SPNB_RETURNS_OTHER, /// Given one NaN input, returns the non-NaN.
414 SPNB_RETURNS_ANY /// Given one NaN input, can return either (or
415 /// it has been determined that no operands can
418 struct SelectPatternResult {
419 SelectPatternFlavor Flavor;
420 SelectPatternNaNBehavior NaNBehavior; /// Only applicable if Flavor is
421 /// SPF_FMINNUM or SPF_FMAXNUM.
422 bool Ordered; /// When implementing this min/max pattern as
423 /// fcmp; select, does the fcmp have to be
426 /// \brief Return true if \p SPF is a min or a max pattern.
427 static bool isMinOrMax(SelectPatternFlavor SPF) {
428 return !(SPF == SPF_UNKNOWN || SPF == SPF_ABS || SPF == SPF_NABS);
431 /// Pattern match integer [SU]MIN, [SU]MAX and ABS idioms, returning the kind
432 /// and providing the out parameter results if we successfully match.
434 /// If CastOp is not nullptr, also match MIN/MAX idioms where the type does
435 /// not match that of the original select. If this is the case, the cast
436 /// operation (one of Trunc,SExt,Zext) that must be done to transform the
437 /// type of LHS and RHS into the type of V is returned in CastOp.
440 /// %1 = icmp slt i32 %a, i32 4
441 /// %2 = sext i32 %a to i64
442 /// %3 = select i1 %1, i64 %2, i64 4
444 /// -> LHS = %a, RHS = i32 4, *CastOp = Instruction::SExt
446 SelectPatternResult matchSelectPattern(Value *V, Value *&LHS, Value *&RHS,
447 Instruction::CastOps *CastOp = nullptr);
449 /// Parse out a conservative ConstantRange from !range metadata.
451 /// E.g. if RangeMD is !{i32 0, i32 10, i32 15, i32 20} then return [0, 20).
452 ConstantRange getConstantRangeFromMetadata(MDNode &RangeMD);
454 /// Return true if RHS is known to be implied true by LHS. Return false if
455 /// RHS is known to be implied false by LHS. Otherwise, return None if no
456 /// implication can be made.
457 /// A & B must be i1 (boolean) values or a vector of such values. Note that
458 /// the truth table for implication is the same as <=u on i1 values (but not
459 /// <=s!). The truth table for both is:
464 Optional<bool> isImpliedCondition(
465 Value *LHS, Value *RHS, const DataLayout &DL, bool InvertAPred = false,
466 unsigned Depth = 0, AssumptionCache *AC = nullptr,
467 const Instruction *CxtI = nullptr, const DominatorTree *DT = nullptr);
468 } // end namespace llvm