1 //===- llvm/Analysis/ValueTracking.h - Walk computations --------*- C++ -*-===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 // This file contains routines that help analyze properties that chains of 10 // computations have. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #ifndef LLVM_ANALYSIS_VALUETRACKING_H 15 #define LLVM_ANALYSIS_VALUETRACKING_H 16 17 #include "llvm/ADT/ArrayRef.h" 18 #include "llvm/ADT/Optional.h" 19 #include "llvm/ADT/SmallSet.h" 20 #include "llvm/IR/Constants.h" 21 #include "llvm/IR/DataLayout.h" 22 #include "llvm/IR/InstrTypes.h" 23 #include "llvm/IR/Intrinsics.h" 24 #include "llvm/IR/Operator.h" 25 #include <cassert> 26 #include <cstdint> 27 28 namespace llvm { 29 30 class AddOperator; 31 class AllocaInst; 32 class APInt; 33 class AssumptionCache; 34 class DominatorTree; 35 class GEPOperator; 36 class IntrinsicInst; 37 class LoadInst; 38 class WithOverflowInst; 39 struct KnownBits; 40 class Loop; 41 class LoopInfo; 42 class MDNode; 43 class OptimizationRemarkEmitter; 44 class StringRef; 45 class TargetLibraryInfo; 46 class Value; 47 48 constexpr unsigned MaxAnalysisRecursionDepth = 6; 49 50 /// Determine which bits of V are known to be either zero or one and return 51 /// them in the KnownZero/KnownOne bit sets. 52 /// 53 /// This function is defined on values with integer type, values with pointer 54 /// type, and vectors of integers. In the case 55 /// where V is a vector, the known zero and known one values are the 56 /// same width as the vector element, and the bit is set only if it is true 57 /// for all of the elements in the vector. 58 void computeKnownBits(const Value *V, KnownBits &Known, 59 const DataLayout &DL, unsigned Depth = 0, 60 AssumptionCache *AC = nullptr, 61 const Instruction *CxtI = nullptr, 62 const DominatorTree *DT = nullptr, 63 OptimizationRemarkEmitter *ORE = nullptr, 64 bool UseInstrInfo = true); 65 66 /// Determine which bits of V are known to be either zero or one and return 67 /// them in the KnownZero/KnownOne bit sets. 68 /// 69 /// This function is defined on values with integer type, values with pointer 70 /// type, and vectors of integers. In the case 71 /// where V is a vector, the known zero and known one values are the 72 /// same width as the vector element, and the bit is set only if it is true 73 /// for all of the demanded elements in the vector. 74 void computeKnownBits(const Value *V, const APInt &DemandedElts, 75 KnownBits &Known, const DataLayout &DL, 76 unsigned Depth = 0, AssumptionCache *AC = nullptr, 77 const Instruction *CxtI = nullptr, 78 const DominatorTree *DT = nullptr, 79 OptimizationRemarkEmitter *ORE = nullptr, 80 bool UseInstrInfo = true); 81 82 /// Returns the known bits rather than passing by reference. 83 KnownBits computeKnownBits(const Value *V, const DataLayout &DL, 84 unsigned Depth = 0, AssumptionCache *AC = nullptr, 85 const Instruction *CxtI = nullptr, 86 const DominatorTree *DT = nullptr, 87 OptimizationRemarkEmitter *ORE = nullptr, 88 bool UseInstrInfo = true); 89 90 /// Returns the known bits rather than passing by reference. 91 KnownBits computeKnownBits(const Value *V, const APInt &DemandedElts, 92 const DataLayout &DL, unsigned Depth = 0, 93 AssumptionCache *AC = nullptr, 94 const Instruction *CxtI = nullptr, 95 const DominatorTree *DT = nullptr, 96 OptimizationRemarkEmitter *ORE = nullptr, 97 bool UseInstrInfo = true); 98 99 /// Compute known bits from the range metadata. 100 /// \p KnownZero the set of bits that are known to be zero 101 /// \p KnownOne the set of bits that are known to be one 102 void computeKnownBitsFromRangeMetadata(const MDNode &Ranges, 103 KnownBits &Known); 104 105 /// Return true if LHS and RHS have no common bits set. 106 bool haveNoCommonBitsSet(const Value *LHS, const Value *RHS, 107 const DataLayout &DL, 108 AssumptionCache *AC = nullptr, 109 const Instruction *CxtI = nullptr, 110 const DominatorTree *DT = nullptr, 111 bool UseInstrInfo = true); 112 113 /// Return true if the given value is known to have exactly one bit set when 114 /// defined. For vectors return true if every element is known to be a power 115 /// of two when defined. Supports values with integer or pointer type and 116 /// vectors of integers. If 'OrZero' is set, then return true if the given 117 /// value is either a power of two or zero. 118 bool isKnownToBeAPowerOfTwo(const Value *V, const DataLayout &DL, 119 bool OrZero = false, unsigned Depth = 0, 120 AssumptionCache *AC = nullptr, 121 const Instruction *CxtI = nullptr, 122 const DominatorTree *DT = nullptr, 123 bool UseInstrInfo = true); 124 125 bool isOnlyUsedInZeroEqualityComparison(const Instruction *CxtI); 126 127 /// Return true if the given value is known to be non-zero when defined. For 128 /// vectors, return true if every element is known to be non-zero when 129 /// defined. For pointers, if the context instruction and dominator tree are 130 /// specified, perform context-sensitive analysis and return true if the 131 /// pointer couldn't possibly be null at the specified instruction. 132 /// Supports values with integer or pointer type and vectors of integers. 133 bool isKnownNonZero(const Value *V, const DataLayout &DL, unsigned Depth = 0, 134 AssumptionCache *AC = nullptr, 135 const Instruction *CxtI = nullptr, 136 const DominatorTree *DT = nullptr, 137 bool UseInstrInfo = true); 138 139 /// Return true if the two given values are negation. 140 /// Currently can recoginze Value pair: 141 /// 1: <X, Y> if X = sub (0, Y) or Y = sub (0, X) 142 /// 2: <X, Y> if X = sub (A, B) and Y = sub (B, A) 143 bool isKnownNegation(const Value *X, const Value *Y, bool NeedNSW = false); 144 145 /// Returns true if the give value is known to be non-negative. 146 bool isKnownNonNegative(const Value *V, const DataLayout &DL, 147 unsigned Depth = 0, 148 AssumptionCache *AC = nullptr, 149 const Instruction *CxtI = nullptr, 150 const DominatorTree *DT = nullptr, 151 bool UseInstrInfo = true); 152 153 /// Returns true if the given value is known be positive (i.e. non-negative 154 /// and non-zero). 155 bool isKnownPositive(const Value *V, const DataLayout &DL, unsigned Depth = 0, 156 AssumptionCache *AC = nullptr, 157 const Instruction *CxtI = nullptr, 158 const DominatorTree *DT = nullptr, 159 bool UseInstrInfo = true); 160 161 /// Returns true if the given value is known be negative (i.e. non-positive 162 /// and non-zero). 163 bool isKnownNegative(const Value *V, const DataLayout &DL, unsigned Depth = 0, 164 AssumptionCache *AC = nullptr, 165 const Instruction *CxtI = nullptr, 166 const DominatorTree *DT = nullptr, 167 bool UseInstrInfo = true); 168 169 /// Return true if the given values are known to be non-equal when defined. 170 /// Supports scalar integer types only. 171 bool isKnownNonEqual(const Value *V1, const Value *V2, const DataLayout &DL, 172 AssumptionCache *AC = nullptr, 173 const Instruction *CxtI = nullptr, 174 const DominatorTree *DT = nullptr, 175 bool UseInstrInfo = true); 176 177 /// Return true if 'V & Mask' is known to be zero. We use this predicate to 178 /// simplify operations downstream. Mask is known to be zero for bits that V 179 /// cannot have. 180 /// 181 /// This function is defined on values with integer type, values with pointer 182 /// type, and vectors of integers. In the case 183 /// where V is a vector, the mask, known zero, and known one values are the 184 /// same width as the vector element, and the bit is set only if it is true 185 /// for all of the elements in the vector. 186 bool MaskedValueIsZero(const Value *V, const APInt &Mask, 187 const DataLayout &DL, 188 unsigned Depth = 0, AssumptionCache *AC = nullptr, 189 const Instruction *CxtI = nullptr, 190 const DominatorTree *DT = nullptr, 191 bool UseInstrInfo = true); 192 193 /// Return the number of times the sign bit of the register is replicated into 194 /// the other bits. We know that at least 1 bit is always equal to the sign 195 /// bit (itself), but other cases can give us information. For example, 196 /// immediately after an "ashr X, 2", we know that the top 3 bits are all 197 /// equal to each other, so we return 3. For vectors, return the number of 198 /// sign bits for the vector element with the mininum number of known sign 199 /// bits. 200 unsigned ComputeNumSignBits(const Value *Op, const DataLayout &DL, 201 unsigned Depth = 0, AssumptionCache *AC = nullptr, 202 const Instruction *CxtI = nullptr, 203 const DominatorTree *DT = nullptr, 204 bool UseInstrInfo = true); 205 206 /// This function computes the integer multiple of Base that equals V. If 207 /// successful, it returns true and returns the multiple in Multiple. If 208 /// unsuccessful, it returns false. Also, if V can be simplified to an 209 /// integer, then the simplified V is returned in Val. Look through sext only 210 /// if LookThroughSExt=true. 211 bool ComputeMultiple(Value *V, unsigned Base, Value *&Multiple, 212 bool LookThroughSExt = false, 213 unsigned Depth = 0); 214 215 /// Map a call instruction to an intrinsic ID. Libcalls which have equivalent 216 /// intrinsics are treated as-if they were intrinsics. 217 Intrinsic::ID getIntrinsicForCallSite(const CallBase &CB, 218 const TargetLibraryInfo *TLI); 219 220 /// Return true if we can prove that the specified FP value is never equal to 221 /// -0.0. 222 bool CannotBeNegativeZero(const Value *V, const TargetLibraryInfo *TLI, 223 unsigned Depth = 0); 224 225 /// Return true if we can prove that the specified FP value is either NaN or 226 /// never less than -0.0. 227 /// 228 /// NaN --> true 229 /// +0 --> true 230 /// -0 --> true 231 /// x > +0 --> true 232 /// x < -0 --> false 233 bool CannotBeOrderedLessThanZero(const Value *V, const TargetLibraryInfo *TLI); 234 235 /// Return true if the floating-point scalar value is not an infinity or if 236 /// the floating-point vector value has no infinities. Return false if a value 237 /// could ever be infinity. 238 bool isKnownNeverInfinity(const Value *V, const TargetLibraryInfo *TLI, 239 unsigned Depth = 0); 240 241 /// Return true if the floating-point scalar value is not a NaN or if the 242 /// floating-point vector value has no NaN elements. Return false if a value 243 /// could ever be NaN. 244 bool isKnownNeverNaN(const Value *V, const TargetLibraryInfo *TLI, 245 unsigned Depth = 0); 246 247 /// Return true if we can prove that the specified FP value's sign bit is 0. 248 /// 249 /// NaN --> true/false (depending on the NaN's sign bit) 250 /// +0 --> true 251 /// -0 --> false 252 /// x > +0 --> true 253 /// x < -0 --> false 254 bool SignBitMustBeZero(const Value *V, const TargetLibraryInfo *TLI); 255 256 /// If the specified value can be set by repeating the same byte in memory, 257 /// return the i8 value that it is represented with. This is true for all i8 258 /// values obviously, but is also true for i32 0, i32 -1, i16 0xF0F0, double 259 /// 0.0 etc. If the value can't be handled with a repeated byte store (e.g. 260 /// i16 0x1234), return null. If the value is entirely undef and padding, 261 /// return undef. 262 Value *isBytewiseValue(Value *V, const DataLayout &DL); 263 264 /// Given an aggregate and an sequence of indices, see if the scalar value 265 /// indexed is already around as a register, for example if it were inserted 266 /// directly into the aggregate. 267 /// 268 /// If InsertBefore is not null, this function will duplicate (modified) 269 /// insertvalues when a part of a nested struct is extracted. 270 Value *FindInsertedValue(Value *V, 271 ArrayRef<unsigned> idx_range, 272 Instruction *InsertBefore = nullptr); 273 274 /// Analyze the specified pointer to see if it can be expressed as a base 275 /// pointer plus a constant offset. Return the base and offset to the caller. 276 /// 277 /// This is a wrapper around Value::stripAndAccumulateConstantOffsets that 278 /// creates and later unpacks the required APInt. 279 inline Value *GetPointerBaseWithConstantOffset(Value *Ptr, int64_t &Offset, 280 const DataLayout &DL, 281 bool AllowNonInbounds = true) { 282 APInt OffsetAPInt(DL.getIndexTypeSizeInBits(Ptr->getType()), 0); 283 Value *Base = 284 Ptr->stripAndAccumulateConstantOffsets(DL, OffsetAPInt, AllowNonInbounds); 285 286 Offset = OffsetAPInt.getSExtValue(); 287 return Base; 288 } 289 inline const Value * 290 GetPointerBaseWithConstantOffset(const Value *Ptr, int64_t &Offset, 291 const DataLayout &DL, 292 bool AllowNonInbounds = true) { 293 return GetPointerBaseWithConstantOffset(const_cast<Value *>(Ptr), Offset, DL, 294 AllowNonInbounds); 295 } 296 297 /// Returns true if the GEP is based on a pointer to a string (array of 298 // \p CharSize integers) and is indexing into this string. 299 bool isGEPBasedOnPointerToString(const GEPOperator *GEP, 300 unsigned CharSize = 8); 301 302 /// Represents offset+length into a ConstantDataArray. 303 struct ConstantDataArraySlice { 304 /// ConstantDataArray pointer. nullptr indicates a zeroinitializer (a valid 305 /// initializer, it just doesn't fit the ConstantDataArray interface). 306 const ConstantDataArray *Array; 307 308 /// Slice starts at this Offset. 309 uint64_t Offset; 310 311 /// Length of the slice. 312 uint64_t Length; 313 314 /// Moves the Offset and adjusts Length accordingly. 315 void move(uint64_t Delta) { 316 assert(Delta < Length); 317 Offset += Delta; 318 Length -= Delta; 319 } 320 321 /// Convenience accessor for elements in the slice. 322 uint64_t operator[](unsigned I) const { 323 return Array==nullptr ? 0 : Array->getElementAsInteger(I + Offset); 324 } 325 }; 326 327 /// Returns true if the value \p V is a pointer into a ConstantDataArray. 328 /// If successful \p Slice will point to a ConstantDataArray info object 329 /// with an appropriate offset. 330 bool getConstantDataArrayInfo(const Value *V, ConstantDataArraySlice &Slice, 331 unsigned ElementSize, uint64_t Offset = 0); 332 333 /// This function computes the length of a null-terminated C string pointed to 334 /// by V. If successful, it returns true and returns the string in Str. If 335 /// unsuccessful, it returns false. This does not include the trailing null 336 /// character by default. If TrimAtNul is set to false, then this returns any 337 /// trailing null characters as well as any other characters that come after 338 /// it. 339 bool getConstantStringInfo(const Value *V, StringRef &Str, 340 uint64_t Offset = 0, bool TrimAtNul = true); 341 342 /// If we can compute the length of the string pointed to by the specified 343 /// pointer, return 'len+1'. If we can't, return 0. 344 uint64_t GetStringLength(const Value *V, unsigned CharSize = 8); 345 346 /// This function returns call pointer argument that is considered the same by 347 /// aliasing rules. You CAN'T use it to replace one value with another. If 348 /// \p MustPreserveNullness is true, the call must preserve the nullness of 349 /// the pointer. 350 const Value *getArgumentAliasingToReturnedPointer(const CallBase *Call, 351 bool MustPreserveNullness); 352 inline Value * 353 getArgumentAliasingToReturnedPointer(CallBase *Call, 354 bool MustPreserveNullness) { 355 return const_cast<Value *>(getArgumentAliasingToReturnedPointer( 356 const_cast<const CallBase *>(Call), MustPreserveNullness)); 357 } 358 359 /// {launder,strip}.invariant.group returns pointer that aliases its argument, 360 /// and it only captures pointer by returning it. 361 /// These intrinsics are not marked as nocapture, because returning is 362 /// considered as capture. The arguments are not marked as returned neither, 363 /// because it would make it useless. If \p MustPreserveNullness is true, 364 /// the intrinsic must preserve the nullness of the pointer. 365 bool isIntrinsicReturningPointerAliasingArgumentWithoutCapturing( 366 const CallBase *Call, bool MustPreserveNullness); 367 368 /// This method strips off any GEP address adjustments and pointer casts from 369 /// the specified value, returning the original object being addressed. Note 370 /// that the returned value has pointer type if the specified value does. If 371 /// the MaxLookup value is non-zero, it limits the number of instructions to 372 /// be stripped off. 373 const Value *getUnderlyingObject(const Value *V, unsigned MaxLookup = 6); 374 inline Value *getUnderlyingObject(Value *V, unsigned MaxLookup = 6) { 375 // Force const to avoid infinite recursion. 376 const Value *VConst = V; 377 return const_cast<Value *>(getUnderlyingObject(VConst, MaxLookup)); 378 } 379 380 /// This method is similar to getUnderlyingObject except that it can 381 /// look through phi and select instructions and return multiple objects. 382 /// 383 /// If LoopInfo is passed, loop phis are further analyzed. If a pointer 384 /// accesses different objects in each iteration, we don't look through the 385 /// phi node. E.g. consider this loop nest: 386 /// 387 /// int **A; 388 /// for (i) 389 /// for (j) { 390 /// A[i][j] = A[i-1][j] * B[j] 391 /// } 392 /// 393 /// This is transformed by Load-PRE to stash away A[i] for the next iteration 394 /// of the outer loop: 395 /// 396 /// Curr = A[0]; // Prev_0 397 /// for (i: 1..N) { 398 /// Prev = Curr; // Prev = PHI (Prev_0, Curr) 399 /// Curr = A[i]; 400 /// for (j: 0..N) { 401 /// Curr[j] = Prev[j] * B[j] 402 /// } 403 /// } 404 /// 405 /// Since A[i] and A[i-1] are independent pointers, getUnderlyingObjects 406 /// should not assume that Curr and Prev share the same underlying object thus 407 /// it shouldn't look through the phi above. 408 void getUnderlyingObjects(const Value *V, 409 SmallVectorImpl<const Value *> &Objects, 410 LoopInfo *LI = nullptr, unsigned MaxLookup = 6); 411 412 /// This is a wrapper around getUnderlyingObjects and adds support for basic 413 /// ptrtoint+arithmetic+inttoptr sequences. 414 bool getUnderlyingObjectsForCodeGen(const Value *V, 415 SmallVectorImpl<Value *> &Objects); 416 417 /// Returns unique alloca where the value comes from, or nullptr. 418 /// If OffsetZero is true check that V points to the begining of the alloca. 419 AllocaInst *findAllocaForValue(Value *V, bool OffsetZero = false); 420 inline const AllocaInst *findAllocaForValue(const Value *V, 421 bool OffsetZero = false) { 422 return findAllocaForValue(const_cast<Value *>(V), OffsetZero); 423 } 424 425 /// Return true if the only users of this pointer are lifetime markers. 426 bool onlyUsedByLifetimeMarkers(const Value *V); 427 428 /// Return true if the only users of this pointer are lifetime markers or 429 /// droppable instructions. 430 bool onlyUsedByLifetimeMarkersOrDroppableInsts(const Value *V); 431 432 /// Return true if speculation of the given load must be suppressed to avoid 433 /// ordering or interfering with an active sanitizer. If not suppressed, 434 /// dereferenceability and alignment must be proven separately. Note: This 435 /// is only needed for raw reasoning; if you use the interface below 436 /// (isSafeToSpeculativelyExecute), this is handled internally. 437 bool mustSuppressSpeculation(const LoadInst &LI); 438 439 /// Return true if the instruction does not have any effects besides 440 /// calculating the result and does not have undefined behavior. 441 /// 442 /// This method never returns true for an instruction that returns true for 443 /// mayHaveSideEffects; however, this method also does some other checks in 444 /// addition. It checks for undefined behavior, like dividing by zero or 445 /// loading from an invalid pointer (but not for undefined results, like a 446 /// shift with a shift amount larger than the width of the result). It checks 447 /// for malloc and alloca because speculatively executing them might cause a 448 /// memory leak. It also returns false for instructions related to control 449 /// flow, specifically terminators and PHI nodes. 450 /// 451 /// If the CtxI is specified this method performs context-sensitive analysis 452 /// and returns true if it is safe to execute the instruction immediately 453 /// before the CtxI. 454 /// 455 /// If the CtxI is NOT specified this method only looks at the instruction 456 /// itself and its operands, so if this method returns true, it is safe to 457 /// move the instruction as long as the correct dominance relationships for 458 /// the operands and users hold. 459 /// 460 /// This method can return true for instructions that read memory; 461 /// for such instructions, moving them may change the resulting value. 462 bool isSafeToSpeculativelyExecute(const Value *V, 463 const Instruction *CtxI = nullptr, 464 const DominatorTree *DT = nullptr, 465 const TargetLibraryInfo *TLI = nullptr); 466 467 /// Returns true if the result or effects of the given instructions \p I 468 /// depend on or influence global memory. 469 /// Memory dependence arises for example if the instruction reads from 470 /// memory or may produce effects or undefined behaviour. Memory dependent 471 /// instructions generally cannot be reorderd with respect to other memory 472 /// dependent instructions or moved into non-dominated basic blocks. 473 /// Instructions which just compute a value based on the values of their 474 /// operands are not memory dependent. 475 bool mayBeMemoryDependent(const Instruction &I); 476 477 /// Return true if it is an intrinsic that cannot be speculated but also 478 /// cannot trap. 479 bool isAssumeLikeIntrinsic(const Instruction *I); 480 481 /// Return true if it is valid to use the assumptions provided by an 482 /// assume intrinsic, I, at the point in the control-flow identified by the 483 /// context instruction, CxtI. 484 bool isValidAssumeForContext(const Instruction *I, const Instruction *CxtI, 485 const DominatorTree *DT = nullptr); 486 487 enum class OverflowResult { 488 /// Always overflows in the direction of signed/unsigned min value. 489 AlwaysOverflowsLow, 490 /// Always overflows in the direction of signed/unsigned max value. 491 AlwaysOverflowsHigh, 492 /// May or may not overflow. 493 MayOverflow, 494 /// Never overflows. 495 NeverOverflows, 496 }; 497 498 OverflowResult computeOverflowForUnsignedMul(const Value *LHS, 499 const Value *RHS, 500 const DataLayout &DL, 501 AssumptionCache *AC, 502 const Instruction *CxtI, 503 const DominatorTree *DT, 504 bool UseInstrInfo = true); 505 OverflowResult computeOverflowForSignedMul(const Value *LHS, const Value *RHS, 506 const DataLayout &DL, 507 AssumptionCache *AC, 508 const Instruction *CxtI, 509 const DominatorTree *DT, 510 bool UseInstrInfo = true); 511 OverflowResult computeOverflowForUnsignedAdd(const Value *LHS, 512 const Value *RHS, 513 const DataLayout &DL, 514 AssumptionCache *AC, 515 const Instruction *CxtI, 516 const DominatorTree *DT, 517 bool UseInstrInfo = true); 518 OverflowResult computeOverflowForSignedAdd(const Value *LHS, const Value *RHS, 519 const DataLayout &DL, 520 AssumptionCache *AC = nullptr, 521 const Instruction *CxtI = nullptr, 522 const DominatorTree *DT = nullptr); 523 /// This version also leverages the sign bit of Add if known. 524 OverflowResult computeOverflowForSignedAdd(const AddOperator *Add, 525 const DataLayout &DL, 526 AssumptionCache *AC = nullptr, 527 const Instruction *CxtI = nullptr, 528 const DominatorTree *DT = nullptr); 529 OverflowResult computeOverflowForUnsignedSub(const Value *LHS, const Value *RHS, 530 const DataLayout &DL, 531 AssumptionCache *AC, 532 const Instruction *CxtI, 533 const DominatorTree *DT); 534 OverflowResult computeOverflowForSignedSub(const Value *LHS, const Value *RHS, 535 const DataLayout &DL, 536 AssumptionCache *AC, 537 const Instruction *CxtI, 538 const DominatorTree *DT); 539 540 /// Returns true if the arithmetic part of the \p WO 's result is 541 /// used only along the paths control dependent on the computation 542 /// not overflowing, \p WO being an <op>.with.overflow intrinsic. 543 bool isOverflowIntrinsicNoWrap(const WithOverflowInst *WO, 544 const DominatorTree &DT); 545 546 547 /// Determine the possible constant range of an integer or vector of integer 548 /// value. This is intended as a cheap, non-recursive check. 549 ConstantRange computeConstantRange(const Value *V, bool UseInstrInfo = true, 550 AssumptionCache *AC = nullptr, 551 const Instruction *CtxI = nullptr, 552 unsigned Depth = 0); 553 554 /// Return true if this function can prove that the instruction I will 555 /// always transfer execution to one of its successors (including the next 556 /// instruction that follows within a basic block). E.g. this is not 557 /// guaranteed for function calls that could loop infinitely. 558 /// 559 /// In other words, this function returns false for instructions that may 560 /// transfer execution or fail to transfer execution in a way that is not 561 /// captured in the CFG nor in the sequence of instructions within a basic 562 /// block. 563 /// 564 /// Undefined behavior is assumed not to happen, so e.g. division is 565 /// guaranteed to transfer execution to the following instruction even 566 /// though division by zero might cause undefined behavior. 567 bool isGuaranteedToTransferExecutionToSuccessor(const Instruction *I); 568 569 /// Returns true if this block does not contain a potential implicit exit. 570 /// This is equivelent to saying that all instructions within the basic block 571 /// are guaranteed to transfer execution to their successor within the basic 572 /// block. This has the same assumptions w.r.t. undefined behavior as the 573 /// instruction variant of this function. 574 bool isGuaranteedToTransferExecutionToSuccessor(const BasicBlock *BB); 575 576 /// Return true if this function can prove that the instruction I 577 /// is executed for every iteration of the loop L. 578 /// 579 /// Note that this currently only considers the loop header. 580 bool isGuaranteedToExecuteForEveryIteration(const Instruction *I, 581 const Loop *L); 582 583 /// Return true if I yields poison or raises UB if any of its operands is 584 /// poison. 585 /// Formally, given I = `r = op v1 v2 .. vN`, propagatesPoison returns true 586 /// if, for all i, r is evaluated to poison or op raises UB if vi = poison. 587 /// If vi is a vector or an aggregate and r is a single value, any poison 588 /// element in vi should make r poison or raise UB. 589 /// To filter out operands that raise UB on poison, you can use 590 /// getGuaranteedNonPoisonOp. 591 bool propagatesPoison(const Operator *I); 592 593 /// Insert operands of I into Ops such that I will trigger undefined behavior 594 /// if I is executed and that operand has a poison value. 595 void getGuaranteedNonPoisonOps(const Instruction *I, 596 SmallPtrSetImpl<const Value *> &Ops); 597 /// Insert operands of I into Ops such that I will trigger undefined behavior 598 /// if I is executed and that operand is not a well-defined value 599 /// (i.e. has undef bits or poison). 600 void getGuaranteedWellDefinedOps(const Instruction *I, 601 SmallPtrSetImpl<const Value *> &Ops); 602 603 /// Return true if the given instruction must trigger undefined behavior 604 /// when I is executed with any operands which appear in KnownPoison holding 605 /// a poison value at the point of execution. 606 bool mustTriggerUB(const Instruction *I, 607 const SmallSet<const Value *, 16>& KnownPoison); 608 609 /// Return true if this function can prove that if Inst is executed 610 /// and yields a poison value or undef bits, then that will trigger 611 /// undefined behavior. 612 /// 613 /// Note that this currently only considers the basic block that is 614 /// the parent of Inst. 615 bool programUndefinedIfUndefOrPoison(const Instruction *Inst); 616 bool programUndefinedIfPoison(const Instruction *Inst); 617 618 /// canCreateUndefOrPoison returns true if Op can create undef or poison from 619 /// non-undef & non-poison operands. 620 /// For vectors, canCreateUndefOrPoison returns true if there is potential 621 /// poison or undef in any element of the result when vectors without 622 /// undef/poison poison are given as operands. 623 /// For example, given `Op = shl <2 x i32> %x, <0, 32>`, this function returns 624 /// true. If Op raises immediate UB but never creates poison or undef 625 /// (e.g. sdiv I, 0), canCreatePoison returns false. 626 /// 627 /// canCreatePoison returns true if Op can create poison from non-poison 628 /// operands. 629 bool canCreateUndefOrPoison(const Operator *Op); 630 bool canCreatePoison(const Operator *Op); 631 632 /// Return true if V is poison given that ValAssumedPoison is already poison. 633 /// For example, if ValAssumedPoison is `icmp X, 10` and V is `icmp X, 5`, 634 /// impliesPoison returns true. 635 bool impliesPoison(const Value *ValAssumedPoison, const Value *V); 636 637 /// Return true if this function can prove that V does not have undef bits 638 /// and is never poison. If V is an aggregate value or vector, check whether 639 /// all elements (except padding) are not undef or poison. 640 /// Note that this is different from canCreateUndefOrPoison because the 641 /// function assumes Op's operands are not poison/undef. 642 /// 643 /// If CtxI and DT are specified this method performs flow-sensitive analysis 644 /// and returns true if it is guaranteed to be never undef or poison 645 /// immediately before the CtxI. 646 bool isGuaranteedNotToBeUndefOrPoison(const Value *V, 647 AssumptionCache *AC = nullptr, 648 const Instruction *CtxI = nullptr, 649 const DominatorTree *DT = nullptr, 650 unsigned Depth = 0); 651 bool isGuaranteedNotToBePoison(const Value *V, AssumptionCache *AC = nullptr, 652 const Instruction *CtxI = nullptr, 653 const DominatorTree *DT = nullptr, 654 unsigned Depth = 0); 655 656 /// Specific patterns of select instructions we can match. 657 enum SelectPatternFlavor { 658 SPF_UNKNOWN = 0, 659 SPF_SMIN, /// Signed minimum 660 SPF_UMIN, /// Unsigned minimum 661 SPF_SMAX, /// Signed maximum 662 SPF_UMAX, /// Unsigned maximum 663 SPF_FMINNUM, /// Floating point minnum 664 SPF_FMAXNUM, /// Floating point maxnum 665 SPF_ABS, /// Absolute value 666 SPF_NABS /// Negated absolute value 667 }; 668 669 /// Behavior when a floating point min/max is given one NaN and one 670 /// non-NaN as input. 671 enum SelectPatternNaNBehavior { 672 SPNB_NA = 0, /// NaN behavior not applicable. 673 SPNB_RETURNS_NAN, /// Given one NaN input, returns the NaN. 674 SPNB_RETURNS_OTHER, /// Given one NaN input, returns the non-NaN. 675 SPNB_RETURNS_ANY /// Given one NaN input, can return either (or 676 /// it has been determined that no operands can 677 /// be NaN). 678 }; 679 680 struct SelectPatternResult { 681 SelectPatternFlavor Flavor; 682 SelectPatternNaNBehavior NaNBehavior; /// Only applicable if Flavor is 683 /// SPF_FMINNUM or SPF_FMAXNUM. 684 bool Ordered; /// When implementing this min/max pattern as 685 /// fcmp; select, does the fcmp have to be 686 /// ordered? 687 688 /// Return true if \p SPF is a min or a max pattern. 689 static bool isMinOrMax(SelectPatternFlavor SPF) { 690 return SPF != SPF_UNKNOWN && SPF != SPF_ABS && SPF != SPF_NABS; 691 } 692 }; 693 694 /// Pattern match integer [SU]MIN, [SU]MAX and ABS idioms, returning the kind 695 /// and providing the out parameter results if we successfully match. 696 /// 697 /// For ABS/NABS, LHS will be set to the input to the abs idiom. RHS will be 698 /// the negation instruction from the idiom. 699 /// 700 /// If CastOp is not nullptr, also match MIN/MAX idioms where the type does 701 /// not match that of the original select. If this is the case, the cast 702 /// operation (one of Trunc,SExt,Zext) that must be done to transform the 703 /// type of LHS and RHS into the type of V is returned in CastOp. 704 /// 705 /// For example: 706 /// %1 = icmp slt i32 %a, i32 4 707 /// %2 = sext i32 %a to i64 708 /// %3 = select i1 %1, i64 %2, i64 4 709 /// 710 /// -> LHS = %a, RHS = i32 4, *CastOp = Instruction::SExt 711 /// 712 SelectPatternResult matchSelectPattern(Value *V, Value *&LHS, Value *&RHS, 713 Instruction::CastOps *CastOp = nullptr, 714 unsigned Depth = 0); 715 716 inline SelectPatternResult 717 matchSelectPattern(const Value *V, const Value *&LHS, const Value *&RHS) { 718 Value *L = const_cast<Value *>(LHS); 719 Value *R = const_cast<Value *>(RHS); 720 auto Result = matchSelectPattern(const_cast<Value *>(V), L, R); 721 LHS = L; 722 RHS = R; 723 return Result; 724 } 725 726 /// Determine the pattern that a select with the given compare as its 727 /// predicate and given values as its true/false operands would match. 728 SelectPatternResult matchDecomposedSelectPattern( 729 CmpInst *CmpI, Value *TrueVal, Value *FalseVal, Value *&LHS, Value *&RHS, 730 Instruction::CastOps *CastOp = nullptr, unsigned Depth = 0); 731 732 /// Return the canonical comparison predicate for the specified 733 /// minimum/maximum flavor. 734 CmpInst::Predicate getMinMaxPred(SelectPatternFlavor SPF, 735 bool Ordered = false); 736 737 /// Return the inverse minimum/maximum flavor of the specified flavor. 738 /// For example, signed minimum is the inverse of signed maximum. 739 SelectPatternFlavor getInverseMinMaxFlavor(SelectPatternFlavor SPF); 740 741 Intrinsic::ID getInverseMinMaxIntrinsic(Intrinsic::ID MinMaxID); 742 743 /// Return the canonical inverse comparison predicate for the specified 744 /// minimum/maximum flavor. 745 CmpInst::Predicate getInverseMinMaxPred(SelectPatternFlavor SPF); 746 747 /// Check if the values in \p VL are select instructions that can be converted 748 /// to a min or max (vector) intrinsic. Returns the intrinsic ID, if such a 749 /// conversion is possible, together with a bool indicating whether all select 750 /// conditions are only used by the selects. Otherwise return 751 /// Intrinsic::not_intrinsic. 752 std::pair<Intrinsic::ID, bool> 753 canConvertToMinOrMaxIntrinsic(ArrayRef<Value *> VL); 754 755 /// Attempt to match a simple first order recurrence cycle of the form: 756 /// %iv = phi Ty [%Start, %Entry], [%Inc, %backedge] 757 /// %inc = binop %iv, %step 758 /// OR 759 /// %iv = phi Ty [%Start, %Entry], [%Inc, %backedge] 760 /// %inc = binop %step, %iv 761 /// 762 /// A first order recurrence is a formula with the form: X_n = f(X_(n-1)) 763 /// 764 /// A couple of notes on subtleties in that definition: 765 /// * The Step does not have to be loop invariant. In math terms, it can 766 /// be a free variable. We allow recurrences with both constant and 767 /// variable coefficients. Callers may wish to filter cases where Step 768 /// does not dominate P. 769 /// * For non-commutative operators, we will match both forms. This 770 /// results in some odd recurrence structures. Callers may wish to filter 771 /// out recurrences where the phi is not the LHS of the returned operator. 772 /// * Because of the structure matched, the caller can assume as a post 773 /// condition of the match the presence of a Loop with P's parent as it's 774 /// header *except* in unreachable code. (Dominance decays in unreachable 775 /// code.) 776 /// 777 /// NOTE: This is intentional simple. If you want the ability to analyze 778 /// non-trivial loop conditons, see ScalarEvolution instead. 779 bool matchSimpleRecurrence(const PHINode *P, BinaryOperator *&BO, 780 Value *&Start, Value *&Step); 781 782 /// Analogous to the above, but starting from the binary operator 783 bool matchSimpleRecurrence(const BinaryOperator *I, PHINode *&P, 784 Value *&Start, Value *&Step); 785 786 /// Return true if RHS is known to be implied true by LHS. Return false if 787 /// RHS is known to be implied false by LHS. Otherwise, return None if no 788 /// implication can be made. 789 /// A & B must be i1 (boolean) values or a vector of such values. Note that 790 /// the truth table for implication is the same as <=u on i1 values (but not 791 /// <=s!). The truth table for both is: 792 /// | T | F (B) 793 /// T | T | F 794 /// F | T | T 795 /// (A) 796 Optional<bool> isImpliedCondition(const Value *LHS, const Value *RHS, 797 const DataLayout &DL, bool LHSIsTrue = true, 798 unsigned Depth = 0); 799 Optional<bool> isImpliedCondition(const Value *LHS, 800 CmpInst::Predicate RHSPred, 801 const Value *RHSOp0, const Value *RHSOp1, 802 const DataLayout &DL, bool LHSIsTrue = true, 803 unsigned Depth = 0); 804 805 /// Return the boolean condition value in the context of the given instruction 806 /// if it is known based on dominating conditions. 807 Optional<bool> isImpliedByDomCondition(const Value *Cond, 808 const Instruction *ContextI, 809 const DataLayout &DL); 810 Optional<bool> isImpliedByDomCondition(CmpInst::Predicate Pred, 811 const Value *LHS, const Value *RHS, 812 const Instruction *ContextI, 813 const DataLayout &DL); 814 815 /// If Ptr1 is provably equal to Ptr2 plus a constant offset, return that 816 /// offset. For example, Ptr1 might be &A[42], and Ptr2 might be &A[40]. In 817 /// this case offset would be -8. 818 Optional<int64_t> isPointerOffset(const Value *Ptr1, const Value *Ptr2, 819 const DataLayout &DL); 820 } // end namespace llvm 821 822 #endif // LLVM_ANALYSIS_VALUETRACKING_H 823
Indexes created Sun Jun 07 00:24:08 UTC 2026