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. moveConstantDataArraySlice315 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 * getArgumentAliasingToReturnedPointer(CallBase * Call,bool MustPreserveNullness)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 Value *getUnderlyingObject(Value *V, unsigned MaxLookup = 6); 374 inline const Value *getUnderlyingObject(const Value *V, 375 unsigned MaxLookup = 6) { 376 return getUnderlyingObject(const_cast<Value *>(V), MaxLookup); 377 } 378 379 /// This method is similar to getUnderlyingObject except that it can 380 /// look through phi and select instructions and return multiple objects. 381 /// 382 /// If LoopInfo is passed, loop phis are further analyzed. If a pointer 383 /// accesses different objects in each iteration, we don't look through the 384 /// phi node. E.g. consider this loop nest: 385 /// 386 /// int **A; 387 /// for (i) 388 /// for (j) { 389 /// A[i][j] = A[i-1][j] * B[j] 390 /// } 391 /// 392 /// This is transformed by Load-PRE to stash away A[i] for the next iteration 393 /// of the outer loop: 394 /// 395 /// Curr = A[0]; // Prev_0 396 /// for (i: 1..N) { 397 /// Prev = Curr; // Prev = PHI (Prev_0, Curr) 398 /// Curr = A[i]; 399 /// for (j: 0..N) { 400 /// Curr[j] = Prev[j] * B[j] 401 /// } 402 /// } 403 /// 404 /// Since A[i] and A[i-1] are independent pointers, getUnderlyingObjects 405 /// should not assume that Curr and Prev share the same underlying object thus 406 /// it shouldn't look through the phi above. 407 void getUnderlyingObjects(const Value *V, 408 SmallVectorImpl<const Value *> &Objects, 409 LoopInfo *LI = nullptr, unsigned MaxLookup = 6); 410 411 /// This is a wrapper around getUnderlyingObjects and adds support for basic 412 /// ptrtoint+arithmetic+inttoptr sequences. 413 bool getUnderlyingObjectsForCodeGen(const Value *V, 414 SmallVectorImpl<Value *> &Objects); 415 416 /// Returns unique alloca where the value comes from, or nullptr. 417 /// If OffsetZero is true check that V points to the begining of the alloca. 418 AllocaInst *findAllocaForValue(Value *V, bool OffsetZero = false); 419 inline const AllocaInst *findAllocaForValue(const Value *V, 420 bool OffsetZero = false) { 421 return findAllocaForValue(const_cast<Value *>(V), OffsetZero); 422 } 423 424 /// Return true if the only users of this pointer are lifetime markers. 425 bool onlyUsedByLifetimeMarkers(const Value *V); 426 427 /// Return true if the only users of this pointer are lifetime markers or 428 /// droppable instructions. 429 bool onlyUsedByLifetimeMarkersOrDroppableInsts(const Value *V); 430 431 /// Return true if speculation of the given load must be suppressed to avoid 432 /// ordering or interfering with an active sanitizer. If not suppressed, 433 /// dereferenceability and alignment must be proven separately. Note: This 434 /// is only needed for raw reasoning; if you use the interface below 435 /// (isSafeToSpeculativelyExecute), this is handled internally. 436 bool mustSuppressSpeculation(const LoadInst &LI); 437 438 /// Return true if the instruction does not have any effects besides 439 /// calculating the result and does not have undefined behavior. 440 /// 441 /// This method never returns true for an instruction that returns true for 442 /// mayHaveSideEffects; however, this method also does some other checks in 443 /// addition. It checks for undefined behavior, like dividing by zero or 444 /// loading from an invalid pointer (but not for undefined results, like a 445 /// shift with a shift amount larger than the width of the result). It checks 446 /// for malloc and alloca because speculatively executing them might cause a 447 /// memory leak. It also returns false for instructions related to control 448 /// flow, specifically terminators and PHI nodes. 449 /// 450 /// If the CtxI is specified this method performs context-sensitive analysis 451 /// and returns true if it is safe to execute the instruction immediately 452 /// before the CtxI. 453 /// 454 /// If the CtxI is NOT specified this method only looks at the instruction 455 /// itself and its operands, so if this method returns true, it is safe to 456 /// move the instruction as long as the correct dominance relationships for 457 /// the operands and users hold. 458 /// 459 /// This method can return true for instructions that read memory; 460 /// for such instructions, moving them may change the resulting value. 461 bool isSafeToSpeculativelyExecute(const Value *V, 462 const Instruction *CtxI = nullptr, 463 const DominatorTree *DT = nullptr); 464 465 /// Returns true if the result or effects of the given instructions \p I 466 /// depend on or influence global memory. 467 /// Memory dependence arises for example if the instruction reads from 468 /// memory or may produce effects or undefined behaviour. Memory dependent 469 /// instructions generally cannot be reorderd with respect to other memory 470 /// dependent instructions or moved into non-dominated basic blocks. 471 /// Instructions which just compute a value based on the values of their 472 /// operands are not memory dependent. 473 bool mayBeMemoryDependent(const Instruction &I); 474 475 /// Return true if it is an intrinsic that cannot be speculated but also 476 /// cannot trap. 477 bool isAssumeLikeIntrinsic(const Instruction *I); 478 479 /// Return true if it is valid to use the assumptions provided by an 480 /// assume intrinsic, I, at the point in the control-flow identified by the 481 /// context instruction, CxtI. 482 bool isValidAssumeForContext(const Instruction *I, const Instruction *CxtI, 483 const DominatorTree *DT = nullptr); 484 485 enum class OverflowResult { 486 /// Always overflows in the direction of signed/unsigned min value. 487 AlwaysOverflowsLow, 488 /// Always overflows in the direction of signed/unsigned max value. 489 AlwaysOverflowsHigh, 490 /// May or may not overflow. 491 MayOverflow, 492 /// Never overflows. 493 NeverOverflows, 494 }; 495 496 OverflowResult computeOverflowForUnsignedMul(const Value *LHS, 497 const Value *RHS, 498 const DataLayout &DL, 499 AssumptionCache *AC, 500 const Instruction *CxtI, 501 const DominatorTree *DT, 502 bool UseInstrInfo = true); 503 OverflowResult computeOverflowForSignedMul(const Value *LHS, const Value *RHS, 504 const DataLayout &DL, 505 AssumptionCache *AC, 506 const Instruction *CxtI, 507 const DominatorTree *DT, 508 bool UseInstrInfo = true); 509 OverflowResult computeOverflowForUnsignedAdd(const Value *LHS, 510 const Value *RHS, 511 const DataLayout &DL, 512 AssumptionCache *AC, 513 const Instruction *CxtI, 514 const DominatorTree *DT, 515 bool UseInstrInfo = true); 516 OverflowResult computeOverflowForSignedAdd(const Value *LHS, const Value *RHS, 517 const DataLayout &DL, 518 AssumptionCache *AC = nullptr, 519 const Instruction *CxtI = nullptr, 520 const DominatorTree *DT = nullptr); 521 /// This version also leverages the sign bit of Add if known. 522 OverflowResult computeOverflowForSignedAdd(const AddOperator *Add, 523 const DataLayout &DL, 524 AssumptionCache *AC = nullptr, 525 const Instruction *CxtI = nullptr, 526 const DominatorTree *DT = nullptr); 527 OverflowResult computeOverflowForUnsignedSub(const Value *LHS, const Value *RHS, 528 const DataLayout &DL, 529 AssumptionCache *AC, 530 const Instruction *CxtI, 531 const DominatorTree *DT); 532 OverflowResult computeOverflowForSignedSub(const Value *LHS, const Value *RHS, 533 const DataLayout &DL, 534 AssumptionCache *AC, 535 const Instruction *CxtI, 536 const DominatorTree *DT); 537 538 /// Returns true if the arithmetic part of the \p WO 's result is 539 /// used only along the paths control dependent on the computation 540 /// not overflowing, \p WO being an <op>.with.overflow intrinsic. 541 bool isOverflowIntrinsicNoWrap(const WithOverflowInst *WO, 542 const DominatorTree &DT); 543 544 545 /// Determine the possible constant range of an integer or vector of integer 546 /// value. This is intended as a cheap, non-recursive check. 547 ConstantRange computeConstantRange(const Value *V, bool UseInstrInfo = true, 548 AssumptionCache *AC = nullptr, 549 const Instruction *CtxI = nullptr, 550 unsigned Depth = 0); 551 552 /// Return true if this function can prove that the instruction I will 553 /// always transfer execution to one of its successors (including the next 554 /// instruction that follows within a basic block). E.g. this is not 555 /// guaranteed for function calls that could loop infinitely. 556 /// 557 /// In other words, this function returns false for instructions that may 558 /// transfer execution or fail to transfer execution in a way that is not 559 /// captured in the CFG nor in the sequence of instructions within a basic 560 /// block. 561 /// 562 /// Undefined behavior is assumed not to happen, so e.g. division is 563 /// guaranteed to transfer execution to the following instruction even 564 /// though division by zero might cause undefined behavior. 565 bool isGuaranteedToTransferExecutionToSuccessor(const Instruction *I); 566 567 /// Returns true if this block does not contain a potential implicit exit. 568 /// This is equivelent to saying that all instructions within the basic block 569 /// are guaranteed to transfer execution to their successor within the basic 570 /// block. This has the same assumptions w.r.t. undefined behavior as the 571 /// instruction variant of this function. 572 bool isGuaranteedToTransferExecutionToSuccessor(const BasicBlock *BB); 573 574 /// Return true if this function can prove that the instruction I 575 /// is executed for every iteration of the loop L. 576 /// 577 /// Note that this currently only considers the loop header. 578 bool isGuaranteedToExecuteForEveryIteration(const Instruction *I, 579 const Loop *L); 580 581 /// Return true if I yields poison or raises UB if any of its operands is 582 /// poison. 583 /// Formally, given I = `r = op v1 v2 .. vN`, propagatesPoison returns true 584 /// if, for all i, r is evaluated to poison or op raises UB if vi = poison. 585 /// To filter out operands that raise UB on poison, you can use 586 /// getGuaranteedNonPoisonOp. 587 bool propagatesPoison(const Operator *I); 588 589 /// Insert operands of I into Ops such that I will trigger undefined behavior 590 /// if I is executed and that operand has a poison value. 591 void getGuaranteedNonPoisonOps(const Instruction *I, 592 SmallPtrSetImpl<const Value *> &Ops); 593 594 /// Return true if the given instruction must trigger undefined behavior 595 /// when I is executed with any operands which appear in KnownPoison holding 596 /// a poison value at the point of execution. 597 bool mustTriggerUB(const Instruction *I, 598 const SmallSet<const Value *, 16>& KnownPoison); 599 600 /// Return true if this function can prove that if Inst is executed 601 /// and yields a poison value or undef bits, then that will trigger 602 /// undefined behavior. 603 /// 604 /// Note that this currently only considers the basic block that is 605 /// the parent of Inst. 606 bool programUndefinedIfUndefOrPoison(const Instruction *Inst); 607 bool programUndefinedIfPoison(const Instruction *Inst); 608 609 /// canCreateUndefOrPoison returns true if Op can create undef or poison from 610 /// non-undef & non-poison operands. 611 /// For vectors, canCreateUndefOrPoison returns true if there is potential 612 /// poison or undef in any element of the result when vectors without 613 /// undef/poison poison are given as operands. 614 /// For example, given `Op = shl <2 x i32> %x, <0, 32>`, this function returns 615 /// true. If Op raises immediate UB but never creates poison or undef 616 /// (e.g. sdiv I, 0), canCreatePoison returns false. 617 /// 618 /// canCreatePoison returns true if Op can create poison from non-poison 619 /// operands. 620 bool canCreateUndefOrPoison(const Operator *Op); 621 bool canCreatePoison(const Operator *Op); 622 623 /// Return true if this function can prove that V does not have undef bits 624 /// and is never poison. If V is an aggregate value or vector, check whether 625 /// all elements (except padding) are not undef or poison. 626 /// Note that this is different from canCreateUndefOrPoison because the 627 /// function assumes Op's operands are not poison/undef. 628 /// 629 /// If CtxI and DT are specified this method performs flow-sensitive analysis 630 /// and returns true if it is guaranteed to be never undef or poison 631 /// immediately before the CtxI. 632 bool isGuaranteedNotToBeUndefOrPoison(const Value *V, 633 AssumptionCache *AC = nullptr, 634 const Instruction *CtxI = nullptr, 635 const DominatorTree *DT = nullptr, 636 unsigned Depth = 0); 637 bool isGuaranteedNotToBePoison(const Value *V, AssumptionCache *AC = nullptr, 638 const Instruction *CtxI = nullptr, 639 const DominatorTree *DT = nullptr, 640 unsigned Depth = 0); 641 642 /// Specific patterns of select instructions we can match. 643 enum SelectPatternFlavor { 644 SPF_UNKNOWN = 0, 645 SPF_SMIN, /// Signed minimum 646 SPF_UMIN, /// Unsigned minimum 647 SPF_SMAX, /// Signed maximum 648 SPF_UMAX, /// Unsigned maximum 649 SPF_FMINNUM, /// Floating point minnum 650 SPF_FMAXNUM, /// Floating point maxnum 651 SPF_ABS, /// Absolute value 652 SPF_NABS /// Negated absolute value 653 }; 654 655 /// Behavior when a floating point min/max is given one NaN and one 656 /// non-NaN as input. 657 enum SelectPatternNaNBehavior { 658 SPNB_NA = 0, /// NaN behavior not applicable. 659 SPNB_RETURNS_NAN, /// Given one NaN input, returns the NaN. 660 SPNB_RETURNS_OTHER, /// Given one NaN input, returns the non-NaN. 661 SPNB_RETURNS_ANY /// Given one NaN input, can return either (or 662 /// it has been determined that no operands can 663 /// be NaN). 664 }; 665 666 struct SelectPatternResult { 667 SelectPatternFlavor Flavor; 668 SelectPatternNaNBehavior NaNBehavior; /// Only applicable if Flavor is 669 /// SPF_FMINNUM or SPF_FMAXNUM. 670 bool Ordered; /// When implementing this min/max pattern as 671 /// fcmp; select, does the fcmp have to be 672 /// ordered? 673 674 /// Return true if \p SPF is a min or a max pattern. isMinOrMaxSelectPatternResult675 static bool isMinOrMax(SelectPatternFlavor SPF) { 676 return SPF != SPF_UNKNOWN && SPF != SPF_ABS && SPF != SPF_NABS; 677 } 678 }; 679 680 /// Pattern match integer [SU]MIN, [SU]MAX and ABS idioms, returning the kind 681 /// and providing the out parameter results if we successfully match. 682 /// 683 /// For ABS/NABS, LHS will be set to the input to the abs idiom. RHS will be 684 /// the negation instruction from the idiom. 685 /// 686 /// If CastOp is not nullptr, also match MIN/MAX idioms where the type does 687 /// not match that of the original select. If this is the case, the cast 688 /// operation (one of Trunc,SExt,Zext) that must be done to transform the 689 /// type of LHS and RHS into the type of V is returned in CastOp. 690 /// 691 /// For example: 692 /// %1 = icmp slt i32 %a, i32 4 693 /// %2 = sext i32 %a to i64 694 /// %3 = select i1 %1, i64 %2, i64 4 695 /// 696 /// -> LHS = %a, RHS = i32 4, *CastOp = Instruction::SExt 697 /// 698 SelectPatternResult matchSelectPattern(Value *V, Value *&LHS, Value *&RHS, 699 Instruction::CastOps *CastOp = nullptr, 700 unsigned Depth = 0); 701 702 inline SelectPatternResult matchSelectPattern(const Value * V,const Value * & LHS,const Value * & RHS)703 matchSelectPattern(const Value *V, const Value *&LHS, const Value *&RHS) { 704 Value *L = const_cast<Value *>(LHS); 705 Value *R = const_cast<Value *>(RHS); 706 auto Result = matchSelectPattern(const_cast<Value *>(V), L, R); 707 LHS = L; 708 RHS = R; 709 return Result; 710 } 711 712 /// Determine the pattern that a select with the given compare as its 713 /// predicate and given values as its true/false operands would match. 714 SelectPatternResult matchDecomposedSelectPattern( 715 CmpInst *CmpI, Value *TrueVal, Value *FalseVal, Value *&LHS, Value *&RHS, 716 Instruction::CastOps *CastOp = nullptr, unsigned Depth = 0); 717 718 /// Return the canonical comparison predicate for the specified 719 /// minimum/maximum flavor. 720 CmpInst::Predicate getMinMaxPred(SelectPatternFlavor SPF, 721 bool Ordered = false); 722 723 /// Return the inverse minimum/maximum flavor of the specified flavor. 724 /// For example, signed minimum is the inverse of signed maximum. 725 SelectPatternFlavor getInverseMinMaxFlavor(SelectPatternFlavor SPF); 726 727 /// Return the canonical inverse comparison predicate for the specified 728 /// minimum/maximum flavor. 729 CmpInst::Predicate getInverseMinMaxPred(SelectPatternFlavor SPF); 730 731 /// Check if the values in \p VL are select instructions that can be converted 732 /// to a min or max (vector) intrinsic. Returns the intrinsic ID, if such a 733 /// conversion is possible, together with a bool indicating whether all select 734 /// conditions are only used by the selects. Otherwise return 735 /// Intrinsic::not_intrinsic. 736 std::pair<Intrinsic::ID, bool> 737 canConvertToMinOrMaxIntrinsic(ArrayRef<Value *> VL); 738 739 /// Return true if RHS is known to be implied true by LHS. Return false if 740 /// RHS is known to be implied false by LHS. Otherwise, return None if no 741 /// implication can be made. 742 /// A & B must be i1 (boolean) values or a vector of such values. Note that 743 /// the truth table for implication is the same as <=u on i1 values (but not 744 /// <=s!). The truth table for both is: 745 /// | T | F (B) 746 /// T | T | F 747 /// F | T | T 748 /// (A) 749 Optional<bool> isImpliedCondition(const Value *LHS, const Value *RHS, 750 const DataLayout &DL, bool LHSIsTrue = true, 751 unsigned Depth = 0); 752 Optional<bool> isImpliedCondition(const Value *LHS, 753 CmpInst::Predicate RHSPred, 754 const Value *RHSOp0, const Value *RHSOp1, 755 const DataLayout &DL, bool LHSIsTrue = true, 756 unsigned Depth = 0); 757 758 /// Return the boolean condition value in the context of the given instruction 759 /// if it is known based on dominating conditions. 760 Optional<bool> isImpliedByDomCondition(const Value *Cond, 761 const Instruction *ContextI, 762 const DataLayout &DL); 763 Optional<bool> isImpliedByDomCondition(CmpInst::Predicate Pred, 764 const Value *LHS, const Value *RHS, 765 const Instruction *ContextI, 766 const DataLayout &DL); 767 768 /// If Ptr1 is provably equal to Ptr2 plus a constant offset, return that 769 /// offset. For example, Ptr1 might be &A[42], and Ptr2 might be &A[40]. In 770 /// this case offset would be -8. 771 Optional<int64_t> isPointerOffset(const Value *Ptr1, const Value *Ptr2, 772 const DataLayout &DL); 773 } // end namespace llvm 774 775 #endif // LLVM_ANALYSIS_VALUETRACKING_H 776