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/SmallSet.h" 19 #include "llvm/IR/Constants.h" 20 #include "llvm/IR/DataLayout.h" 21 #include "llvm/IR/InstrTypes.h" 22 #include "llvm/IR/Intrinsics.h" 23 #include <cassert> 24 #include <cstdint> 25 26 namespace llvm { 27 28 class Operator; 29 class AddOperator; 30 class AllocaInst; 31 class APInt; 32 class AssumptionCache; 33 class DominatorTree; 34 class GEPOperator; 35 class LoadInst; 36 class WithOverflowInst; 37 struct KnownBits; 38 class Loop; 39 class LoopInfo; 40 class MDNode; 41 class OptimizationRemarkEmitter; 42 class StringRef; 43 class TargetLibraryInfo; 44 class Value; 45 46 constexpr unsigned MaxAnalysisRecursionDepth = 6; 47 48 /// Determine which bits of V are known to be either zero or one and return 49 /// them in the KnownZero/KnownOne bit sets. 50 /// 51 /// This function is defined on values with integer type, values with pointer 52 /// type, and vectors of integers. In the case 53 /// where V is a vector, the known zero and known one values are the 54 /// same width as the vector element, and the bit is set only if it is true 55 /// for all of the elements in the vector. 56 void computeKnownBits(const Value *V, KnownBits &Known, const DataLayout &DL, 57 unsigned Depth = 0, AssumptionCache *AC = nullptr, 58 const Instruction *CxtI = nullptr, 59 const DominatorTree *DT = nullptr, 60 OptimizationRemarkEmitter *ORE = nullptr, 61 bool UseInstrInfo = true); 62 63 /// Determine which bits of V are known to be either zero or one and return 64 /// them in the KnownZero/KnownOne bit sets. 65 /// 66 /// This function is defined on values with integer type, values with pointer 67 /// type, and vectors of integers. In the case 68 /// where V is a vector, the known zero and known one values are the 69 /// same width as the vector element, and the bit is set only if it is true 70 /// for all of the demanded elements in the vector. 71 void computeKnownBits(const Value *V, const APInt &DemandedElts, 72 KnownBits &Known, const DataLayout &DL, 73 unsigned Depth = 0, AssumptionCache *AC = nullptr, 74 const Instruction *CxtI = nullptr, 75 const DominatorTree *DT = nullptr, 76 OptimizationRemarkEmitter *ORE = nullptr, 77 bool UseInstrInfo = true); 78 79 /// Returns the known bits rather than passing by reference. 80 KnownBits computeKnownBits(const Value *V, const DataLayout &DL, 81 unsigned Depth = 0, AssumptionCache *AC = nullptr, 82 const Instruction *CxtI = nullptr, 83 const DominatorTree *DT = nullptr, 84 OptimizationRemarkEmitter *ORE = nullptr, 85 bool UseInstrInfo = true); 86 87 /// Returns the known bits rather than passing by reference. 88 KnownBits computeKnownBits(const Value *V, const APInt &DemandedElts, 89 const DataLayout &DL, unsigned Depth = 0, 90 AssumptionCache *AC = nullptr, 91 const Instruction *CxtI = nullptr, 92 const DominatorTree *DT = nullptr, 93 OptimizationRemarkEmitter *ORE = nullptr, 94 bool UseInstrInfo = true); 95 96 /// Compute known bits from the range metadata. 97 /// \p KnownZero the set of bits that are known to be zero 98 /// \p KnownOne the set of bits that are known to be one 99 void computeKnownBitsFromRangeMetadata(const MDNode &Ranges, KnownBits &Known); 100 101 /// Return true if LHS and RHS have no common bits set. 102 bool haveNoCommonBitsSet(const Value *LHS, const Value *RHS, 103 const DataLayout &DL, AssumptionCache *AC = nullptr, 104 const Instruction *CxtI = nullptr, 105 const DominatorTree *DT = nullptr, 106 bool UseInstrInfo = true); 107 108 /// Return true if the given value is known to have exactly one bit set when 109 /// defined. For vectors return true if every element is known to be a power 110 /// of two when defined. Supports values with integer or pointer type and 111 /// vectors of integers. If 'OrZero' is set, then return true if the given 112 /// value is either a power of two or zero. 113 bool isKnownToBeAPowerOfTwo(const Value *V, const DataLayout &DL, 114 bool OrZero = false, unsigned Depth = 0, 115 AssumptionCache *AC = nullptr, 116 const Instruction *CxtI = nullptr, 117 const DominatorTree *DT = nullptr, 118 bool UseInstrInfo = true); 119 120 bool isOnlyUsedInZeroEqualityComparison(const Instruction *CxtI); 121 122 /// Return true if the given value is known to be non-zero when defined. For 123 /// vectors, return true if every element is known to be non-zero when 124 /// defined. For pointers, if the context instruction and dominator tree are 125 /// specified, perform context-sensitive analysis and return true if the 126 /// pointer couldn't possibly be null at the specified instruction. 127 /// Supports values with integer or pointer type and vectors of integers. 128 bool isKnownNonZero(const Value *V, const DataLayout &DL, unsigned Depth = 0, 129 AssumptionCache *AC = nullptr, 130 const Instruction *CxtI = nullptr, 131 const DominatorTree *DT = nullptr, 132 bool UseInstrInfo = true); 133 134 /// Return true if the two given values are negation. 135 /// Currently can recoginze Value pair: 136 /// 1: <X, Y> if X = sub (0, Y) or Y = sub (0, X) 137 /// 2: <X, Y> if X = sub (A, B) and Y = sub (B, A) 138 bool isKnownNegation(const Value *X, const Value *Y, bool NeedNSW = false); 139 140 /// Returns true if the give value is known to be non-negative. 141 bool isKnownNonNegative(const Value *V, const DataLayout &DL, 142 unsigned Depth = 0, AssumptionCache *AC = nullptr, 143 const Instruction *CxtI = nullptr, 144 const DominatorTree *DT = nullptr, 145 bool UseInstrInfo = true); 146 147 /// Returns true if the given value is known be positive (i.e. non-negative 148 /// and non-zero). 149 bool isKnownPositive(const Value *V, const DataLayout &DL, unsigned Depth = 0, 150 AssumptionCache *AC = nullptr, 151 const Instruction *CxtI = nullptr, 152 const DominatorTree *DT = nullptr, 153 bool UseInstrInfo = true); 154 155 /// Returns true if the given value is known be negative (i.e. non-positive 156 /// and non-zero). 157 bool isKnownNegative(const Value *V, const DataLayout &DL, unsigned Depth = 0, 158 AssumptionCache *AC = nullptr, 159 const Instruction *CxtI = nullptr, 160 const DominatorTree *DT = nullptr, 161 bool UseInstrInfo = true); 162 163 /// Return true if the given values are known to be non-equal when defined. 164 /// Supports scalar integer types only. 165 bool isKnownNonEqual(const Value *V1, const Value *V2, const DataLayout &DL, 166 AssumptionCache *AC = nullptr, 167 const Instruction *CxtI = nullptr, 168 const DominatorTree *DT = nullptr, 169 bool UseInstrInfo = true); 170 171 /// Return true if 'V & Mask' is known to be zero. We use this predicate to 172 /// simplify operations downstream. Mask is known to be zero for bits that V 173 /// cannot have. 174 /// 175 /// This function is defined on values with integer type, values with pointer 176 /// type, and vectors of integers. In the case 177 /// where V is a vector, the mask, known zero, and known one values are the 178 /// same width as the vector element, and the bit is set only if it is true 179 /// for all of the elements in the vector. 180 bool MaskedValueIsZero(const Value *V, const APInt &Mask, const DataLayout &DL, 181 unsigned Depth = 0, AssumptionCache *AC = nullptr, 182 const Instruction *CxtI = nullptr, 183 const DominatorTree *DT = nullptr, 184 bool UseInstrInfo = true); 185 186 /// Return the number of times the sign bit of the register is replicated into 187 /// the other bits. We know that at least 1 bit is always equal to the sign 188 /// bit (itself), but other cases can give us information. For example, 189 /// immediately after an "ashr X, 2", we know that the top 3 bits are all 190 /// equal to each other, so we return 3. For vectors, return the number of 191 /// sign bits for the vector element with the mininum number of known sign 192 /// bits. 193 unsigned ComputeNumSignBits(const Value *Op, const DataLayout &DL, 194 unsigned Depth = 0, AssumptionCache *AC = nullptr, 195 const Instruction *CxtI = nullptr, 196 const DominatorTree *DT = nullptr, 197 bool UseInstrInfo = true); 198 199 /// Get the upper bound on bit size for this Value \p Op as a signed integer. 200 /// i.e. x == sext(trunc(x to MaxSignificantBits) to bitwidth(x)). 201 /// Similar to the APInt::getSignificantBits function. 202 unsigned ComputeMaxSignificantBits(const Value *Op, const DataLayout &DL, 203 unsigned Depth = 0, 204 AssumptionCache *AC = nullptr, 205 const Instruction *CxtI = nullptr, 206 const DominatorTree *DT = nullptr); 207 208 /// Map a call instruction to an intrinsic ID. Libcalls which have equivalent 209 /// intrinsics are treated as-if they were intrinsics. 210 Intrinsic::ID getIntrinsicForCallSite(const CallBase &CB, 211 const TargetLibraryInfo *TLI); 212 213 /// Return true if we can prove that the specified FP value is never equal to 214 /// -0.0. 215 bool CannotBeNegativeZero(const Value *V, const TargetLibraryInfo *TLI, 216 unsigned Depth = 0); 217 218 /// Return true if we can prove that the specified FP value is either NaN or 219 /// never less than -0.0. 220 /// 221 /// NaN --> true 222 /// +0 --> true 223 /// -0 --> true 224 /// x > +0 --> true 225 /// x < -0 --> false 226 bool CannotBeOrderedLessThanZero(const Value *V, const TargetLibraryInfo *TLI); 227 228 /// Return true if the floating-point scalar value is not an infinity or if 229 /// the floating-point vector value has no infinities. Return false if a value 230 /// could ever be infinity. 231 bool isKnownNeverInfinity(const Value *V, const TargetLibraryInfo *TLI, 232 unsigned Depth = 0); 233 234 /// Return true if the floating-point scalar value is not a NaN or if the 235 /// floating-point vector value has no NaN elements. Return false if a value 236 /// could ever be NaN. 237 bool isKnownNeverNaN(const Value *V, const TargetLibraryInfo *TLI, 238 unsigned Depth = 0); 239 240 /// Return true if we can prove that the specified FP value's sign bit is 0. 241 /// 242 /// NaN --> true/false (depending on the NaN's sign bit) 243 /// +0 --> true 244 /// -0 --> false 245 /// x > +0 --> true 246 /// x < -0 --> false 247 bool SignBitMustBeZero(const Value *V, const TargetLibraryInfo *TLI); 248 249 /// If the specified value can be set by repeating the same byte in memory, 250 /// return the i8 value that it is represented with. This is true for all i8 251 /// values obviously, but is also true for i32 0, i32 -1, i16 0xF0F0, double 252 /// 0.0 etc. If the value can't be handled with a repeated byte store (e.g. 253 /// i16 0x1234), return null. If the value is entirely undef and padding, 254 /// return undef. 255 Value *isBytewiseValue(Value *V, const DataLayout &DL); 256 257 /// Given an aggregate and an sequence of indices, see if the scalar value 258 /// indexed is already around as a register, for example if it were inserted 259 /// directly into the aggregate. 260 /// 261 /// If InsertBefore is not null, this function will duplicate (modified) 262 /// insertvalues when a part of a nested struct is extracted. 263 Value *FindInsertedValue(Value *V, ArrayRef<unsigned> idx_range, 264 Instruction *InsertBefore = nullptr); 265 266 /// Analyze the specified pointer to see if it can be expressed as a base 267 /// pointer plus a constant offset. Return the base and offset to the caller. 268 /// 269 /// This is a wrapper around Value::stripAndAccumulateConstantOffsets that 270 /// creates and later unpacks the required APInt. 271 inline Value *GetPointerBaseWithConstantOffset(Value *Ptr, int64_t &Offset, 272 const DataLayout &DL, 273 bool AllowNonInbounds = true) { 274 APInt OffsetAPInt(DL.getIndexTypeSizeInBits(Ptr->getType()), 0); 275 Value *Base = 276 Ptr->stripAndAccumulateConstantOffsets(DL, OffsetAPInt, AllowNonInbounds); 277 278 Offset = OffsetAPInt.getSExtValue(); 279 return Base; 280 } 281 inline const Value * 282 GetPointerBaseWithConstantOffset(const Value *Ptr, int64_t &Offset, 283 const DataLayout &DL, 284 bool AllowNonInbounds = true) { 285 return GetPointerBaseWithConstantOffset(const_cast<Value *>(Ptr), Offset, DL, 286 AllowNonInbounds); 287 } 288 289 /// Returns true if the GEP is based on a pointer to a string (array of 290 // \p CharSize integers) and is indexing into this string. 291 bool isGEPBasedOnPointerToString(const GEPOperator *GEP, unsigned CharSize = 8); 292 293 /// Represents offset+length into a ConstantDataArray. 294 struct ConstantDataArraySlice { 295 /// ConstantDataArray pointer. nullptr indicates a zeroinitializer (a valid 296 /// initializer, it just doesn't fit the ConstantDataArray interface). 297 const ConstantDataArray *Array; 298 299 /// Slice starts at this Offset. 300 uint64_t Offset; 301 302 /// Length of the slice. 303 uint64_t Length; 304 305 /// Moves the Offset and adjusts Length accordingly. 306 void move(uint64_t Delta) { 307 assert(Delta < Length); 308 Offset += Delta; 309 Length -= Delta; 310 } 311 312 /// Convenience accessor for elements in the slice. 313 uint64_t operator[](unsigned I) const { 314 return Array == nullptr ? 0 : Array->getElementAsInteger(I + Offset); 315 } 316 }; 317 318 /// Returns true if the value \p V is a pointer into a ConstantDataArray. 319 /// If successful \p Slice will point to a ConstantDataArray info object 320 /// with an appropriate offset. 321 bool getConstantDataArrayInfo(const Value *V, ConstantDataArraySlice &Slice, 322 unsigned ElementSize, uint64_t Offset = 0); 323 324 /// This function computes the length of a null-terminated C string pointed to 325 /// by V. If successful, it returns true and returns the string in Str. If 326 /// unsuccessful, it returns false. This does not include the trailing null 327 /// character by default. If TrimAtNul is set to false, then this returns any 328 /// trailing null characters as well as any other characters that come after 329 /// it. 330 bool getConstantStringInfo(const Value *V, StringRef &Str, 331 bool TrimAtNul = true); 332 333 /// If we can compute the length of the string pointed to by the specified 334 /// pointer, return 'len+1'. If we can't, return 0. 335 uint64_t GetStringLength(const Value *V, unsigned CharSize = 8); 336 337 /// This function returns call pointer argument that is considered the same by 338 /// aliasing rules. You CAN'T use it to replace one value with another. If 339 /// \p MustPreserveNullness is true, the call must preserve the nullness of 340 /// the pointer. 341 const Value *getArgumentAliasingToReturnedPointer(const CallBase *Call, 342 bool MustPreserveNullness); 343 inline Value *getArgumentAliasingToReturnedPointer(CallBase *Call, 344 bool MustPreserveNullness) { 345 return const_cast<Value *>(getArgumentAliasingToReturnedPointer( 346 const_cast<const CallBase *>(Call), MustPreserveNullness)); 347 } 348 349 /// {launder,strip}.invariant.group returns pointer that aliases its argument, 350 /// and it only captures pointer by returning it. 351 /// These intrinsics are not marked as nocapture, because returning is 352 /// considered as capture. The arguments are not marked as returned neither, 353 /// because it would make it useless. If \p MustPreserveNullness is true, 354 /// the intrinsic must preserve the nullness of the pointer. 355 bool isIntrinsicReturningPointerAliasingArgumentWithoutCapturing( 356 const CallBase *Call, bool MustPreserveNullness); 357 358 /// This method strips off any GEP address adjustments and pointer casts from 359 /// the specified value, returning the original object being addressed. Note 360 /// that the returned value has pointer type if the specified value does. If 361 /// the MaxLookup value is non-zero, it limits the number of instructions to 362 /// be stripped off. 363 const Value *getUnderlyingObject(const Value *V, unsigned MaxLookup = 6); 364 inline Value *getUnderlyingObject(Value *V, unsigned MaxLookup = 6) { 365 // Force const to avoid infinite recursion. 366 const Value *VConst = V; 367 return const_cast<Value *>(getUnderlyingObject(VConst, MaxLookup)); 368 } 369 370 /// This method is similar to getUnderlyingObject except that it can 371 /// look through phi and select instructions and return multiple objects. 372 /// 373 /// If LoopInfo is passed, loop phis are further analyzed. If a pointer 374 /// accesses different objects in each iteration, we don't look through the 375 /// phi node. E.g. consider this loop nest: 376 /// 377 /// int **A; 378 /// for (i) 379 /// for (j) { 380 /// A[i][j] = A[i-1][j] * B[j] 381 /// } 382 /// 383 /// This is transformed by Load-PRE to stash away A[i] for the next iteration 384 /// of the outer loop: 385 /// 386 /// Curr = A[0]; // Prev_0 387 /// for (i: 1..N) { 388 /// Prev = Curr; // Prev = PHI (Prev_0, Curr) 389 /// Curr = A[i]; 390 /// for (j: 0..N) { 391 /// Curr[j] = Prev[j] * B[j] 392 /// } 393 /// } 394 /// 395 /// Since A[i] and A[i-1] are independent pointers, getUnderlyingObjects 396 /// should not assume that Curr and Prev share the same underlying object thus 397 /// it shouldn't look through the phi above. 398 void getUnderlyingObjects(const Value *V, 399 SmallVectorImpl<const Value *> &Objects, 400 LoopInfo *LI = nullptr, unsigned MaxLookup = 6); 401 402 /// This is a wrapper around getUnderlyingObjects and adds support for basic 403 /// ptrtoint+arithmetic+inttoptr sequences. 404 bool getUnderlyingObjectsForCodeGen(const Value *V, 405 SmallVectorImpl<Value *> &Objects); 406 407 /// Returns unique alloca where the value comes from, or nullptr. 408 /// If OffsetZero is true check that V points to the begining of the alloca. 409 AllocaInst *findAllocaForValue(Value *V, bool OffsetZero = false); 410 inline const AllocaInst *findAllocaForValue(const Value *V, 411 bool OffsetZero = false) { 412 return findAllocaForValue(const_cast<Value *>(V), OffsetZero); 413 } 414 415 /// Return true if the only users of this pointer are lifetime markers. 416 bool onlyUsedByLifetimeMarkers(const Value *V); 417 418 /// Return true if the only users of this pointer are lifetime markers or 419 /// droppable instructions. 420 bool onlyUsedByLifetimeMarkersOrDroppableInsts(const Value *V); 421 422 /// Return true if speculation of the given load must be suppressed to avoid 423 /// ordering or interfering with an active sanitizer. If not suppressed, 424 /// dereferenceability and alignment must be proven separately. Note: This 425 /// is only needed for raw reasoning; if you use the interface below 426 /// (isSafeToSpeculativelyExecute), this is handled internally. 427 bool mustSuppressSpeculation(const LoadInst &LI); 428 429 /// Return true if the instruction does not have any effects besides 430 /// calculating the result and does not have undefined behavior. 431 /// 432 /// This method never returns true for an instruction that returns true for 433 /// mayHaveSideEffects; however, this method also does some other checks in 434 /// addition. It checks for undefined behavior, like dividing by zero or 435 /// loading from an invalid pointer (but not for undefined results, like a 436 /// shift with a shift amount larger than the width of the result). It checks 437 /// for malloc and alloca because speculatively executing them might cause a 438 /// memory leak. It also returns false for instructions related to control 439 /// flow, specifically terminators and PHI nodes. 440 /// 441 /// If the CtxI is specified this method performs context-sensitive analysis 442 /// and returns true if it is safe to execute the instruction immediately 443 /// before the CtxI. 444 /// 445 /// If the CtxI is NOT specified this method only looks at the instruction 446 /// itself and its operands, so if this method returns true, it is safe to 447 /// move the instruction as long as the correct dominance relationships for 448 /// the operands and users hold. 449 /// 450 /// This method can return true for instructions that read memory; 451 /// for such instructions, moving them may change the resulting value. 452 bool isSafeToSpeculativelyExecute(const Instruction *I, 453 const Instruction *CtxI = nullptr, 454 AssumptionCache *AC = nullptr, 455 const DominatorTree *DT = nullptr, 456 const TargetLibraryInfo *TLI = nullptr); 457 458 /// This returns the same result as isSafeToSpeculativelyExecute if Opcode is 459 /// the actual opcode of Inst. If the provided and actual opcode differ, the 460 /// function (virtually) overrides the opcode of Inst with the provided 461 /// Opcode. There are come constraints in this case: 462 /// * If Opcode has a fixed number of operands (eg, as binary operators do), 463 /// then Inst has to have at least as many leading operands. The function 464 /// will ignore all trailing operands beyond that number. 465 /// * If Opcode allows for an arbitrary number of operands (eg, as CallInsts 466 /// do), then all operands are considered. 467 /// * The virtual instruction has to satisfy all typing rules of the provided 468 /// Opcode. 469 /// * This function is pessimistic in the following sense: If one actually 470 /// materialized the virtual instruction, then isSafeToSpeculativelyExecute 471 /// may say that the materialized instruction is speculatable whereas this 472 /// function may have said that the instruction wouldn't be speculatable. 473 /// This behavior is a shortcoming in the current implementation and not 474 /// intentional. 475 bool isSafeToSpeculativelyExecuteWithOpcode( 476 unsigned Opcode, const Instruction *Inst, const Instruction *CtxI = nullptr, 477 AssumptionCache *AC = nullptr, const DominatorTree *DT = nullptr, 478 const TargetLibraryInfo *TLI = nullptr); 479 480 /// Returns true if the result or effects of the given instructions \p I 481 /// depend values not reachable through the def use graph. 482 /// * Memory dependence arises for example if the instruction reads from 483 /// memory or may produce effects or undefined behaviour. Memory dependent 484 /// instructions generally cannot be reorderd with respect to other memory 485 /// dependent instructions. 486 /// * Control dependence arises for example if the instruction may fault 487 /// if lifted above a throwing call or infinite loop. 488 bool mayHaveNonDefUseDependency(const Instruction &I); 489 490 /// Return true if it is an intrinsic that cannot be speculated but also 491 /// cannot trap. 492 bool isAssumeLikeIntrinsic(const Instruction *I); 493 494 /// Return true if it is valid to use the assumptions provided by an 495 /// assume intrinsic, I, at the point in the control-flow identified by the 496 /// context instruction, CxtI. 497 bool isValidAssumeForContext(const Instruction *I, const Instruction *CxtI, 498 const DominatorTree *DT = nullptr); 499 500 enum class OverflowResult { 501 /// Always overflows in the direction of signed/unsigned min value. 502 AlwaysOverflowsLow, 503 /// Always overflows in the direction of signed/unsigned max value. 504 AlwaysOverflowsHigh, 505 /// May or may not overflow. 506 MayOverflow, 507 /// Never overflows. 508 NeverOverflows, 509 }; 510 511 OverflowResult computeOverflowForUnsignedMul(const Value *LHS, const Value *RHS, 512 const DataLayout &DL, 513 AssumptionCache *AC, 514 const Instruction *CxtI, 515 const DominatorTree *DT, 516 bool UseInstrInfo = true); 517 OverflowResult computeOverflowForSignedMul(const Value *LHS, const Value *RHS, 518 const DataLayout &DL, 519 AssumptionCache *AC, 520 const Instruction *CxtI, 521 const DominatorTree *DT, 522 bool UseInstrInfo = true); 523 OverflowResult computeOverflowForUnsignedAdd(const Value *LHS, const Value *RHS, 524 const DataLayout &DL, 525 AssumptionCache *AC, 526 const Instruction *CxtI, 527 const DominatorTree *DT, 528 bool UseInstrInfo = true); 529 OverflowResult computeOverflowForSignedAdd(const Value *LHS, const Value *RHS, 530 const DataLayout &DL, 531 AssumptionCache *AC = nullptr, 532 const Instruction *CxtI = nullptr, 533 const DominatorTree *DT = nullptr); 534 /// This version also leverages the sign bit of Add if known. 535 OverflowResult computeOverflowForSignedAdd(const AddOperator *Add, 536 const DataLayout &DL, 537 AssumptionCache *AC = nullptr, 538 const Instruction *CxtI = nullptr, 539 const DominatorTree *DT = nullptr); 540 OverflowResult computeOverflowForUnsignedSub(const Value *LHS, const Value *RHS, 541 const DataLayout &DL, 542 AssumptionCache *AC, 543 const Instruction *CxtI, 544 const DominatorTree *DT); 545 OverflowResult computeOverflowForSignedSub(const Value *LHS, const Value *RHS, 546 const DataLayout &DL, 547 AssumptionCache *AC, 548 const Instruction *CxtI, 549 const DominatorTree *DT); 550 551 /// Returns true if the arithmetic part of the \p WO 's result is 552 /// used only along the paths control dependent on the computation 553 /// not overflowing, \p WO being an <op>.with.overflow intrinsic. 554 bool isOverflowIntrinsicNoWrap(const WithOverflowInst *WO, 555 const DominatorTree &DT); 556 557 /// Determine the possible constant range of an integer or vector of integer 558 /// value. This is intended as a cheap, non-recursive check. 559 ConstantRange computeConstantRange(const Value *V, bool ForSigned, 560 bool UseInstrInfo = true, 561 AssumptionCache *AC = nullptr, 562 const Instruction *CtxI = nullptr, 563 const DominatorTree *DT = nullptr, 564 unsigned Depth = 0); 565 566 /// Return true if this function can prove that the instruction I will 567 /// always transfer execution to one of its successors (including the next 568 /// instruction that follows within a basic block). E.g. this is not 569 /// guaranteed for function calls that could loop infinitely. 570 /// 571 /// In other words, this function returns false for instructions that may 572 /// transfer execution or fail to transfer execution in a way that is not 573 /// captured in the CFG nor in the sequence of instructions within a basic 574 /// block. 575 /// 576 /// Undefined behavior is assumed not to happen, so e.g. division is 577 /// guaranteed to transfer execution to the following instruction even 578 /// though division by zero might cause undefined behavior. 579 bool isGuaranteedToTransferExecutionToSuccessor(const Instruction *I); 580 581 /// Returns true if this block does not contain a potential implicit exit. 582 /// This is equivelent to saying that all instructions within the basic block 583 /// are guaranteed to transfer execution to their successor within the basic 584 /// block. This has the same assumptions w.r.t. undefined behavior as the 585 /// instruction variant of this function. 586 bool isGuaranteedToTransferExecutionToSuccessor(const BasicBlock *BB); 587 588 /// Return true if every instruction in the range (Begin, End) is 589 /// guaranteed to transfer execution to its static successor. \p ScanLimit 590 /// bounds the search to avoid scanning huge blocks. 591 bool isGuaranteedToTransferExecutionToSuccessor( 592 BasicBlock::const_iterator Begin, BasicBlock::const_iterator End, 593 unsigned ScanLimit = 32); 594 595 /// Same as previous, but with range expressed via iterator_range. 596 bool isGuaranteedToTransferExecutionToSuccessor( 597 iterator_range<BasicBlock::const_iterator> Range, unsigned ScanLimit = 32); 598 599 /// Return true if this function can prove that the instruction I 600 /// is executed for every iteration of the loop L. 601 /// 602 /// Note that this currently only considers the loop header. 603 bool isGuaranteedToExecuteForEveryIteration(const Instruction *I, 604 const Loop *L); 605 606 /// Return true if \p PoisonOp's user yields poison or raises UB if its 607 /// operand \p PoisonOp is poison. 608 /// 609 /// If \p PoisonOp is a vector or an aggregate and the operation's result is a 610 /// single value, any poison element in /p PoisonOp should make the result 611 /// poison or raise UB. 612 /// 613 /// To filter out operands that raise UB on poison, you can use 614 /// getGuaranteedNonPoisonOp. 615 bool propagatesPoison(const Use &PoisonOp); 616 617 /// Insert operands of I into Ops such that I will trigger undefined behavior 618 /// if I is executed and that operand has a poison value. 619 void getGuaranteedNonPoisonOps(const Instruction *I, 620 SmallVectorImpl<const Value *> &Ops); 621 622 /// Insert operands of I into Ops such that I will trigger undefined behavior 623 /// if I is executed and that operand is not a well-defined value 624 /// (i.e. has undef bits or poison). 625 void getGuaranteedWellDefinedOps(const Instruction *I, 626 SmallVectorImpl<const Value *> &Ops); 627 628 /// Return true if the given instruction must trigger undefined behavior 629 /// when I is executed with any operands which appear in KnownPoison holding 630 /// a poison value at the point of execution. 631 bool mustTriggerUB(const Instruction *I, 632 const SmallSet<const Value *, 16> &KnownPoison); 633 634 /// Return true if this function can prove that if Inst is executed 635 /// and yields a poison value or undef bits, then that will trigger 636 /// undefined behavior. 637 /// 638 /// Note that this currently only considers the basic block that is 639 /// the parent of Inst. 640 bool programUndefinedIfUndefOrPoison(const Instruction *Inst); 641 bool programUndefinedIfPoison(const Instruction *Inst); 642 643 /// canCreateUndefOrPoison returns true if Op can create undef or poison from 644 /// non-undef & non-poison operands. 645 /// For vectors, canCreateUndefOrPoison returns true if there is potential 646 /// poison or undef in any element of the result when vectors without 647 /// undef/poison poison are given as operands. 648 /// For example, given `Op = shl <2 x i32> %x, <0, 32>`, this function returns 649 /// true. If Op raises immediate UB but never creates poison or undef 650 /// (e.g. sdiv I, 0), canCreatePoison returns false. 651 /// 652 /// \p ConsiderFlagsAndMetadata controls whether poison producing flags and 653 /// metadata on the instruction are considered. This can be used to see if the 654 /// instruction could still introduce undef or poison even without poison 655 /// generating flags and metadata which might be on the instruction. 656 /// (i.e. could the result of Op->dropPoisonGeneratingFlags() still create 657 /// poison or undef) 658 /// 659 /// canCreatePoison returns true if Op can create poison from non-poison 660 /// operands. 661 bool canCreateUndefOrPoison(const Operator *Op, 662 bool ConsiderFlagsAndMetadata = true); 663 bool canCreatePoison(const Operator *Op, bool ConsiderFlagsAndMetadata = true); 664 665 /// Return true if V is poison given that ValAssumedPoison is already poison. 666 /// For example, if ValAssumedPoison is `icmp X, 10` and V is `icmp X, 5`, 667 /// impliesPoison returns true. 668 bool impliesPoison(const Value *ValAssumedPoison, const Value *V); 669 670 /// Return true if this function can prove that V does not have undef bits 671 /// and is never poison. If V is an aggregate value or vector, check whether 672 /// all elements (except padding) are not undef or poison. 673 /// Note that this is different from canCreateUndefOrPoison because the 674 /// function assumes Op's operands are not poison/undef. 675 /// 676 /// If CtxI and DT are specified this method performs flow-sensitive analysis 677 /// and returns true if it is guaranteed to be never undef or poison 678 /// immediately before the CtxI. 679 bool isGuaranteedNotToBeUndefOrPoison(const Value *V, 680 AssumptionCache *AC = nullptr, 681 const Instruction *CtxI = nullptr, 682 const DominatorTree *DT = nullptr, 683 unsigned Depth = 0); 684 bool isGuaranteedNotToBePoison(const Value *V, AssumptionCache *AC = nullptr, 685 const Instruction *CtxI = nullptr, 686 const DominatorTree *DT = nullptr, 687 unsigned Depth = 0); 688 689 /// Specific patterns of select instructions we can match. 690 enum SelectPatternFlavor { 691 SPF_UNKNOWN = 0, 692 SPF_SMIN, /// Signed minimum 693 SPF_UMIN, /// Unsigned minimum 694 SPF_SMAX, /// Signed maximum 695 SPF_UMAX, /// Unsigned maximum 696 SPF_FMINNUM, /// Floating point minnum 697 SPF_FMAXNUM, /// Floating point maxnum 698 SPF_ABS, /// Absolute value 699 SPF_NABS /// Negated absolute value 700 }; 701 702 /// Behavior when a floating point min/max is given one NaN and one 703 /// non-NaN as input. 704 enum SelectPatternNaNBehavior { 705 SPNB_NA = 0, /// NaN behavior not applicable. 706 SPNB_RETURNS_NAN, /// Given one NaN input, returns the NaN. 707 SPNB_RETURNS_OTHER, /// Given one NaN input, returns the non-NaN. 708 SPNB_RETURNS_ANY /// Given one NaN input, can return either (or 709 /// it has been determined that no operands can 710 /// be NaN). 711 }; 712 713 struct SelectPatternResult { 714 SelectPatternFlavor Flavor; 715 SelectPatternNaNBehavior NaNBehavior; /// Only applicable if Flavor is 716 /// SPF_FMINNUM or SPF_FMAXNUM. 717 bool Ordered; /// When implementing this min/max pattern as 718 /// fcmp; select, does the fcmp have to be 719 /// ordered? 720 721 /// Return true if \p SPF is a min or a max pattern. 722 static bool isMinOrMax(SelectPatternFlavor SPF) { 723 return SPF != SPF_UNKNOWN && SPF != SPF_ABS && SPF != SPF_NABS; 724 } 725 }; 726 727 /// Pattern match integer [SU]MIN, [SU]MAX and ABS idioms, returning the kind 728 /// and providing the out parameter results if we successfully match. 729 /// 730 /// For ABS/NABS, LHS will be set to the input to the abs idiom. RHS will be 731 /// the negation instruction from the idiom. 732 /// 733 /// If CastOp is not nullptr, also match MIN/MAX idioms where the type does 734 /// not match that of the original select. If this is the case, the cast 735 /// operation (one of Trunc,SExt,Zext) that must be done to transform the 736 /// type of LHS and RHS into the type of V is returned in CastOp. 737 /// 738 /// For example: 739 /// %1 = icmp slt i32 %a, i32 4 740 /// %2 = sext i32 %a to i64 741 /// %3 = select i1 %1, i64 %2, i64 4 742 /// 743 /// -> LHS = %a, RHS = i32 4, *CastOp = Instruction::SExt 744 /// 745 SelectPatternResult matchSelectPattern(Value *V, Value *&LHS, Value *&RHS, 746 Instruction::CastOps *CastOp = nullptr, 747 unsigned Depth = 0); 748 749 inline SelectPatternResult matchSelectPattern(const Value *V, const Value *&LHS, 750 const Value *&RHS) { 751 Value *L = const_cast<Value *>(LHS); 752 Value *R = const_cast<Value *>(RHS); 753 auto Result = matchSelectPattern(const_cast<Value *>(V), L, R); 754 LHS = L; 755 RHS = R; 756 return Result; 757 } 758 759 /// Determine the pattern that a select with the given compare as its 760 /// predicate and given values as its true/false operands would match. 761 SelectPatternResult matchDecomposedSelectPattern( 762 CmpInst *CmpI, Value *TrueVal, Value *FalseVal, Value *&LHS, Value *&RHS, 763 Instruction::CastOps *CastOp = nullptr, unsigned Depth = 0); 764 765 /// Return the canonical comparison predicate for the specified 766 /// minimum/maximum flavor. 767 CmpInst::Predicate getMinMaxPred(SelectPatternFlavor SPF, bool Ordered = false); 768 769 /// Return the inverse minimum/maximum flavor of the specified flavor. 770 /// For example, signed minimum is the inverse of signed maximum. 771 SelectPatternFlavor getInverseMinMaxFlavor(SelectPatternFlavor SPF); 772 773 Intrinsic::ID getInverseMinMaxIntrinsic(Intrinsic::ID MinMaxID); 774 775 /// Return the minimum or maximum constant value for the specified integer 776 /// min/max flavor and type. 777 APInt getMinMaxLimit(SelectPatternFlavor SPF, unsigned BitWidth); 778 779 /// Check if the values in \p VL are select instructions that can be converted 780 /// to a min or max (vector) intrinsic. Returns the intrinsic ID, if such a 781 /// conversion is possible, together with a bool indicating whether all select 782 /// conditions are only used by the selects. Otherwise return 783 /// Intrinsic::not_intrinsic. 784 std::pair<Intrinsic::ID, bool> 785 canConvertToMinOrMaxIntrinsic(ArrayRef<Value *> VL); 786 787 /// Attempt to match a simple first order recurrence cycle of the form: 788 /// %iv = phi Ty [%Start, %Entry], [%Inc, %backedge] 789 /// %inc = binop %iv, %step 790 /// OR 791 /// %iv = phi Ty [%Start, %Entry], [%Inc, %backedge] 792 /// %inc = binop %step, %iv 793 /// 794 /// A first order recurrence is a formula with the form: X_n = f(X_(n-1)) 795 /// 796 /// A couple of notes on subtleties in that definition: 797 /// * The Step does not have to be loop invariant. In math terms, it can 798 /// be a free variable. We allow recurrences with both constant and 799 /// variable coefficients. Callers may wish to filter cases where Step 800 /// does not dominate P. 801 /// * For non-commutative operators, we will match both forms. This 802 /// results in some odd recurrence structures. Callers may wish to filter 803 /// out recurrences where the phi is not the LHS of the returned operator. 804 /// * Because of the structure matched, the caller can assume as a post 805 /// condition of the match the presence of a Loop with P's parent as it's 806 /// header *except* in unreachable code. (Dominance decays in unreachable 807 /// code.) 808 /// 809 /// NOTE: This is intentional simple. If you want the ability to analyze 810 /// non-trivial loop conditons, see ScalarEvolution instead. 811 bool matchSimpleRecurrence(const PHINode *P, BinaryOperator *&BO, Value *&Start, 812 Value *&Step); 813 814 /// Analogous to the above, but starting from the binary operator 815 bool matchSimpleRecurrence(const BinaryOperator *I, PHINode *&P, Value *&Start, 816 Value *&Step); 817 818 /// Return true if RHS is known to be implied true by LHS. Return false if 819 /// RHS is known to be implied false by LHS. Otherwise, return std::nullopt if 820 /// no implication can be made. A & B must be i1 (boolean) values or a vector of 821 /// such values. Note that the truth table for implication is the same as <=u on 822 /// i1 values (but not 823 /// <=s!). The truth table for both is: 824 /// | T | F (B) 825 /// T | T | F 826 /// F | T | T 827 /// (A) 828 std::optional<bool> isImpliedCondition(const Value *LHS, const Value *RHS, 829 const DataLayout &DL, 830 bool LHSIsTrue = true, 831 unsigned Depth = 0); 832 std::optional<bool> isImpliedCondition(const Value *LHS, 833 CmpInst::Predicate RHSPred, 834 const Value *RHSOp0, const Value *RHSOp1, 835 const DataLayout &DL, 836 bool LHSIsTrue = true, 837 unsigned Depth = 0); 838 839 /// Return the boolean condition value in the context of the given instruction 840 /// if it is known based on dominating conditions. 841 std::optional<bool> isImpliedByDomCondition(const Value *Cond, 842 const Instruction *ContextI, 843 const DataLayout &DL); 844 std::optional<bool> isImpliedByDomCondition(CmpInst::Predicate Pred, 845 const Value *LHS, const Value *RHS, 846 const Instruction *ContextI, 847 const DataLayout &DL); 848 849 /// If Ptr1 is provably equal to Ptr2 plus a constant offset, return that 850 /// offset. For example, Ptr1 might be &A[42], and Ptr2 might be &A[40]. In 851 /// this case offset would be -8. 852 std::optional<int64_t> isPointerOffset(const Value *Ptr1, const Value *Ptr2, 853 const DataLayout &DL); 854 } // end namespace llvm 855 856 #endif // LLVM_ANALYSIS_VALUETRACKING_H 857