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 LoadInst; 37 class WithOverflowInst; 38 struct KnownBits; 39 class Loop; 40 class LoopInfo; 41 class MDNode; 42 class OptimizationRemarkEmitter; 43 class StringRef; 44 class TargetLibraryInfo; 45 class Value; 46 47 constexpr unsigned MaxAnalysisRecursionDepth = 6; 48 49 /// Determine which bits of V are known to be either zero or one and return 50 /// them in the KnownZero/KnownOne bit sets. 51 /// 52 /// This function is defined on values with integer type, values with pointer 53 /// type, and vectors of integers. In the case 54 /// where V is a vector, the known zero and known one values are the 55 /// same width as the vector element, and the bit is set only if it is true 56 /// for all of the elements in the vector. 57 void computeKnownBits(const Value *V, KnownBits &Known, 58 const DataLayout &DL, unsigned Depth = 0, 59 AssumptionCache *AC = nullptr, 60 const Instruction *CxtI = nullptr, 61 const DominatorTree *DT = nullptr, 62 OptimizationRemarkEmitter *ORE = nullptr, 63 bool UseInstrInfo = true); 64 65 /// Determine which bits of V are known to be either zero or one and return 66 /// them in the KnownZero/KnownOne bit sets. 67 /// 68 /// This function is defined on values with integer type, values with pointer 69 /// type, and vectors of integers. In the case 70 /// where V is a vector, the known zero and known one values are the 71 /// same width as the vector element, and the bit is set only if it is true 72 /// for all of the demanded elements in the vector. 73 void computeKnownBits(const Value *V, const APInt &DemandedElts, 74 KnownBits &Known, const DataLayout &DL, 75 unsigned Depth = 0, AssumptionCache *AC = nullptr, 76 const Instruction *CxtI = nullptr, 77 const DominatorTree *DT = nullptr, 78 OptimizationRemarkEmitter *ORE = nullptr, 79 bool UseInstrInfo = true); 80 81 /// Returns the known bits rather than passing by reference. 82 KnownBits computeKnownBits(const Value *V, const DataLayout &DL, 83 unsigned Depth = 0, AssumptionCache *AC = nullptr, 84 const Instruction *CxtI = nullptr, 85 const DominatorTree *DT = nullptr, 86 OptimizationRemarkEmitter *ORE = nullptr, 87 bool UseInstrInfo = true); 88 89 /// Returns the known bits rather than passing by reference. 90 KnownBits computeKnownBits(const Value *V, const APInt &DemandedElts, 91 const DataLayout &DL, unsigned Depth = 0, 92 AssumptionCache *AC = nullptr, 93 const Instruction *CxtI = nullptr, 94 const DominatorTree *DT = nullptr, 95 OptimizationRemarkEmitter *ORE = nullptr, 96 bool UseInstrInfo = true); 97 98 /// Compute known bits from the range metadata. 99 /// \p KnownZero the set of bits that are known to be zero 100 /// \p KnownOne the set of bits that are known to be one 101 void computeKnownBitsFromRangeMetadata(const MDNode &Ranges, 102 KnownBits &Known); 103 104 /// Return true if LHS and RHS have no common bits set. 105 bool haveNoCommonBitsSet(const Value *LHS, const Value *RHS, 106 const DataLayout &DL, 107 AssumptionCache *AC = nullptr, 108 const Instruction *CxtI = nullptr, 109 const DominatorTree *DT = nullptr, 110 bool UseInstrInfo = true); 111 112 /// Return true if the given value is known to have exactly one bit set when 113 /// defined. For vectors return true if every element is known to be a power 114 /// of two when defined. Supports values with integer or pointer type and 115 /// vectors of integers. If 'OrZero' is set, then return true if the given 116 /// value is either a power of two or zero. 117 bool isKnownToBeAPowerOfTwo(const Value *V, const DataLayout &DL, 118 bool OrZero = false, unsigned Depth = 0, 119 AssumptionCache *AC = nullptr, 120 const Instruction *CxtI = nullptr, 121 const DominatorTree *DT = nullptr, 122 bool UseInstrInfo = true); 123 124 bool isOnlyUsedInZeroEqualityComparison(const Instruction *CxtI); 125 126 /// Return true if the given value is known to be non-zero when defined. For 127 /// vectors, return true if every element is known to be non-zero when 128 /// defined. For pointers, if the context instruction and dominator tree are 129 /// specified, perform context-sensitive analysis and return true if the 130 /// pointer couldn't possibly be null at the specified instruction. 131 /// Supports values with integer or pointer type and vectors of integers. 132 bool isKnownNonZero(const Value *V, const DataLayout &DL, unsigned Depth = 0, 133 AssumptionCache *AC = nullptr, 134 const Instruction *CxtI = nullptr, 135 const DominatorTree *DT = nullptr, 136 bool UseInstrInfo = true); 137 138 /// Return true if the two given values are negation. 139 /// Currently can recoginze Value pair: 140 /// 1: <X, Y> if X = sub (0, Y) or Y = sub (0, X) 141 /// 2: <X, Y> if X = sub (A, B) and Y = sub (B, A) 142 bool isKnownNegation(const Value *X, const Value *Y, bool NeedNSW = false); 143 144 /// Returns true if the give value is known to be non-negative. 145 bool isKnownNonNegative(const Value *V, const DataLayout &DL, 146 unsigned Depth = 0, 147 AssumptionCache *AC = nullptr, 148 const Instruction *CxtI = nullptr, 149 const DominatorTree *DT = nullptr, 150 bool UseInstrInfo = true); 151 152 /// Returns true if the given value is known be positive (i.e. non-negative 153 /// and non-zero). 154 bool isKnownPositive(const Value *V, const DataLayout &DL, unsigned Depth = 0, 155 AssumptionCache *AC = nullptr, 156 const Instruction *CxtI = nullptr, 157 const DominatorTree *DT = nullptr, 158 bool UseInstrInfo = true); 159 160 /// Returns true if the given value is known be negative (i.e. non-positive 161 /// and non-zero). 162 bool isKnownNegative(const Value *V, const DataLayout &DL, unsigned Depth = 0, 163 AssumptionCache *AC = nullptr, 164 const Instruction *CxtI = nullptr, 165 const DominatorTree *DT = nullptr, 166 bool UseInstrInfo = true); 167 168 /// Return true if the given values are known to be non-equal when defined. 169 /// Supports scalar integer types only. 170 bool isKnownNonEqual(const Value *V1, const Value *V2, const DataLayout &DL, 171 AssumptionCache *AC = nullptr, 172 const Instruction *CxtI = nullptr, 173 const DominatorTree *DT = nullptr, 174 bool UseInstrInfo = true); 175 176 /// Return true if 'V & Mask' is known to be zero. We use this predicate to 177 /// simplify operations downstream. Mask is known to be zero for bits that V 178 /// cannot have. 179 /// 180 /// This function is defined on values with integer type, values with pointer 181 /// type, and vectors of integers. In the case 182 /// where V is a vector, the mask, known zero, and known one values are the 183 /// same width as the vector element, and the bit is set only if it is true 184 /// for all of the elements in the vector. 185 bool MaskedValueIsZero(const Value *V, const APInt &Mask, 186 const DataLayout &DL, 187 unsigned Depth = 0, AssumptionCache *AC = nullptr, 188 const Instruction *CxtI = nullptr, 189 const DominatorTree *DT = nullptr, 190 bool UseInstrInfo = true); 191 192 /// Return the number of times the sign bit of the register is replicated into 193 /// the other bits. We know that at least 1 bit is always equal to the sign 194 /// bit (itself), but other cases can give us information. For example, 195 /// immediately after an "ashr X, 2", we know that the top 3 bits are all 196 /// equal to each other, so we return 3. For vectors, return the number of 197 /// sign bits for the vector element with the mininum number of known sign 198 /// bits. 199 unsigned ComputeNumSignBits(const Value *Op, const DataLayout &DL, 200 unsigned Depth = 0, AssumptionCache *AC = nullptr, 201 const Instruction *CxtI = nullptr, 202 const DominatorTree *DT = nullptr, 203 bool UseInstrInfo = true); 204 205 /// Get the upper bound on bit size for this Value \p Op as a signed integer. 206 /// i.e. x == sext(trunc(x to MaxSignificantBits) to bitwidth(x)). 207 /// Similar to the APInt::getSignificantBits function. 208 unsigned ComputeMaxSignificantBits(const Value *Op, const DataLayout &DL, 209 unsigned Depth = 0, 210 AssumptionCache *AC = nullptr, 211 const Instruction *CxtI = nullptr, 212 const DominatorTree *DT = nullptr); 213 214 /// Map a call instruction to an intrinsic ID. Libcalls which have equivalent 215 /// intrinsics are treated as-if they were intrinsics. 216 Intrinsic::ID getIntrinsicForCallSite(const CallBase &CB, 217 const TargetLibraryInfo *TLI); 218 219 /// Return true if we can prove that the specified FP value is never equal to 220 /// -0.0. 221 bool CannotBeNegativeZero(const Value *V, const TargetLibraryInfo *TLI, 222 unsigned Depth = 0); 223 224 /// Return true if we can prove that the specified FP value is either NaN or 225 /// never less than -0.0. 226 /// 227 /// NaN --> true 228 /// +0 --> true 229 /// -0 --> true 230 /// x > +0 --> true 231 /// x < -0 --> false 232 bool CannotBeOrderedLessThanZero(const Value *V, const TargetLibraryInfo *TLI); 233 234 /// Return true if the floating-point scalar value is not an infinity or if 235 /// the floating-point vector value has no infinities. Return false if a value 236 /// could ever be infinity. 237 bool isKnownNeverInfinity(const Value *V, const TargetLibraryInfo *TLI, 238 unsigned Depth = 0); 239 240 /// Return true if the floating-point scalar value is not a NaN or if the 241 /// floating-point vector value has no NaN elements. Return false if a value 242 /// could ever be NaN. 243 bool isKnownNeverNaN(const Value *V, const TargetLibraryInfo *TLI, 244 unsigned Depth = 0); 245 246 /// Return true if we can prove that the specified FP value's sign bit is 0. 247 /// 248 /// NaN --> true/false (depending on the NaN's sign bit) 249 /// +0 --> true 250 /// -0 --> false 251 /// x > +0 --> true 252 /// x < -0 --> false 253 bool SignBitMustBeZero(const Value *V, const TargetLibraryInfo *TLI); 254 255 /// If the specified value can be set by repeating the same byte in memory, 256 /// return the i8 value that it is represented with. This is true for all i8 257 /// values obviously, but is also true for i32 0, i32 -1, i16 0xF0F0, double 258 /// 0.0 etc. If the value can't be handled with a repeated byte store (e.g. 259 /// i16 0x1234), return null. If the value is entirely undef and padding, 260 /// return undef. 261 Value *isBytewiseValue(Value *V, const DataLayout &DL); 262 263 /// Given an aggregate and an sequence of indices, see if the scalar value 264 /// indexed is already around as a register, for example if it were inserted 265 /// directly into the aggregate. 266 /// 267 /// If InsertBefore is not null, this function will duplicate (modified) 268 /// insertvalues when a part of a nested struct is extracted. 269 Value *FindInsertedValue(Value *V, 270 ArrayRef<unsigned> idx_range, 271 Instruction *InsertBefore = nullptr); 272 273 /// Analyze the specified pointer to see if it can be expressed as a base 274 /// pointer plus a constant offset. Return the base and offset to the caller. 275 /// 276 /// This is a wrapper around Value::stripAndAccumulateConstantOffsets that 277 /// creates and later unpacks the required APInt. 278 inline Value *GetPointerBaseWithConstantOffset(Value *Ptr, int64_t &Offset, 279 const DataLayout &DL, 280 bool AllowNonInbounds = true) { 281 APInt OffsetAPInt(DL.getIndexTypeSizeInBits(Ptr->getType()), 0); 282 Value *Base = 283 Ptr->stripAndAccumulateConstantOffsets(DL, OffsetAPInt, AllowNonInbounds); 284 285 Offset = OffsetAPInt.getSExtValue(); 286 return Base; 287 } 288 inline const Value * 289 GetPointerBaseWithConstantOffset(const Value *Ptr, int64_t &Offset, 290 const DataLayout &DL, 291 bool AllowNonInbounds = true) { 292 return GetPointerBaseWithConstantOffset(const_cast<Value *>(Ptr), Offset, DL, 293 AllowNonInbounds); 294 } 295 296 /// Returns true if the GEP is based on a pointer to a string (array of 297 // \p CharSize integers) and is indexing into this string. 298 bool isGEPBasedOnPointerToString(const GEPOperator *GEP, 299 unsigned CharSize = 8); 300 301 /// Represents offset+length into a ConstantDataArray. 302 struct ConstantDataArraySlice { 303 /// ConstantDataArray pointer. nullptr indicates a zeroinitializer (a valid 304 /// initializer, it just doesn't fit the ConstantDataArray interface). 305 const ConstantDataArray *Array; 306 307 /// Slice starts at this Offset. 308 uint64_t Offset; 309 310 /// Length of the slice. 311 uint64_t Length; 312 313 /// Moves the Offset and adjusts Length accordingly. 314 void move(uint64_t Delta) { 315 assert(Delta < Length); 316 Offset += Delta; 317 Length -= Delta; 318 } 319 320 /// Convenience accessor for elements in the slice. 321 uint64_t operator[](unsigned I) const { 322 return Array==nullptr ? 0 : Array->getElementAsInteger(I + Offset); 323 } 324 }; 325 326 /// Returns true if the value \p V is a pointer into a ConstantDataArray. 327 /// If successful \p Slice will point to a ConstantDataArray info object 328 /// with an appropriate offset. 329 bool getConstantDataArrayInfo(const Value *V, ConstantDataArraySlice &Slice, 330 unsigned ElementSize, uint64_t Offset = 0); 331 332 /// This function computes the length of a null-terminated C string pointed to 333 /// by V. If successful, it returns true and returns the string in Str. If 334 /// unsuccessful, it returns false. This does not include the trailing null 335 /// character by default. If TrimAtNul is set to false, then this returns any 336 /// trailing null characters as well as any other characters that come after 337 /// it. 338 bool getConstantStringInfo(const Value *V, StringRef &Str, 339 uint64_t Offset = 0, bool TrimAtNul = true); 340 341 /// If we can compute the length of the string pointed to by the specified 342 /// pointer, return 'len+1'. If we can't, return 0. 343 uint64_t GetStringLength(const Value *V, unsigned CharSize = 8); 344 345 /// This function returns call pointer argument that is considered the same by 346 /// aliasing rules. You CAN'T use it to replace one value with another. If 347 /// \p MustPreserveNullness is true, the call must preserve the nullness of 348 /// the pointer. 349 const Value *getArgumentAliasingToReturnedPointer(const CallBase *Call, 350 bool MustPreserveNullness); 351 inline Value * 352 getArgumentAliasingToReturnedPointer(CallBase *Call, 353 bool MustPreserveNullness) { 354 return const_cast<Value *>(getArgumentAliasingToReturnedPointer( 355 const_cast<const CallBase *>(Call), MustPreserveNullness)); 356 } 357 358 /// {launder,strip}.invariant.group returns pointer that aliases its argument, 359 /// and it only captures pointer by returning it. 360 /// These intrinsics are not marked as nocapture, because returning is 361 /// considered as capture. The arguments are not marked as returned neither, 362 /// because it would make it useless. If \p MustPreserveNullness is true, 363 /// the intrinsic must preserve the nullness of the pointer. 364 bool isIntrinsicReturningPointerAliasingArgumentWithoutCapturing( 365 const CallBase *Call, bool MustPreserveNullness); 366 367 /// This method strips off any GEP address adjustments and pointer casts from 368 /// the specified value, returning the original object being addressed. Note 369 /// that the returned value has pointer type if the specified value does. If 370 /// the MaxLookup value is non-zero, it limits the number of instructions to 371 /// be stripped off. 372 const Value *getUnderlyingObject(const Value *V, unsigned MaxLookup = 6); 373 inline Value *getUnderlyingObject(Value *V, unsigned MaxLookup = 6) { 374 // Force const to avoid infinite recursion. 375 const Value *VConst = V; 376 return const_cast<Value *>(getUnderlyingObject(VConst, 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 const TargetLibraryInfo *TLI = nullptr); 465 466 /// Returns true if the result or effects of the given instructions \p I 467 /// depend on or influence global memory. 468 /// Memory dependence arises for example if the instruction reads from 469 /// memory or may produce effects or undefined behaviour. Memory dependent 470 /// instructions generally cannot be reorderd with respect to other memory 471 /// dependent instructions or moved into non-dominated basic blocks. 472 /// Instructions which just compute a value based on the values of their 473 /// operands are not memory dependent. 474 bool mayBeMemoryDependent(const Instruction &I); 475 476 /// Return true if it is an intrinsic that cannot be speculated but also 477 /// cannot trap. 478 bool isAssumeLikeIntrinsic(const Instruction *I); 479 480 /// Return true if it is valid to use the assumptions provided by an 481 /// assume intrinsic, I, at the point in the control-flow identified by the 482 /// context instruction, CxtI. 483 bool isValidAssumeForContext(const Instruction *I, const Instruction *CxtI, 484 const DominatorTree *DT = nullptr); 485 486 enum class OverflowResult { 487 /// Always overflows in the direction of signed/unsigned min value. 488 AlwaysOverflowsLow, 489 /// Always overflows in the direction of signed/unsigned max value. 490 AlwaysOverflowsHigh, 491 /// May or may not overflow. 492 MayOverflow, 493 /// Never overflows. 494 NeverOverflows, 495 }; 496 497 OverflowResult computeOverflowForUnsignedMul(const Value *LHS, 498 const Value *RHS, 499 const DataLayout &DL, 500 AssumptionCache *AC, 501 const Instruction *CxtI, 502 const DominatorTree *DT, 503 bool UseInstrInfo = true); 504 OverflowResult computeOverflowForSignedMul(const Value *LHS, const Value *RHS, 505 const DataLayout &DL, 506 AssumptionCache *AC, 507 const Instruction *CxtI, 508 const DominatorTree *DT, 509 bool UseInstrInfo = true); 510 OverflowResult computeOverflowForUnsignedAdd(const Value *LHS, 511 const Value *RHS, 512 const DataLayout &DL, 513 AssumptionCache *AC, 514 const Instruction *CxtI, 515 const DominatorTree *DT, 516 bool UseInstrInfo = true); 517 OverflowResult computeOverflowForSignedAdd(const Value *LHS, const Value *RHS, 518 const DataLayout &DL, 519 AssumptionCache *AC = nullptr, 520 const Instruction *CxtI = nullptr, 521 const DominatorTree *DT = nullptr); 522 /// This version also leverages the sign bit of Add if known. 523 OverflowResult computeOverflowForSignedAdd(const AddOperator *Add, 524 const DataLayout &DL, 525 AssumptionCache *AC = nullptr, 526 const Instruction *CxtI = nullptr, 527 const DominatorTree *DT = nullptr); 528 OverflowResult computeOverflowForUnsignedSub(const Value *LHS, const Value *RHS, 529 const DataLayout &DL, 530 AssumptionCache *AC, 531 const Instruction *CxtI, 532 const DominatorTree *DT); 533 OverflowResult computeOverflowForSignedSub(const Value *LHS, const Value *RHS, 534 const DataLayout &DL, 535 AssumptionCache *AC, 536 const Instruction *CxtI, 537 const DominatorTree *DT); 538 539 /// Returns true if the arithmetic part of the \p WO 's result is 540 /// used only along the paths control dependent on the computation 541 /// not overflowing, \p WO being an <op>.with.overflow intrinsic. 542 bool isOverflowIntrinsicNoWrap(const WithOverflowInst *WO, 543 const DominatorTree &DT); 544 545 546 /// Determine the possible constant range of an integer or vector of integer 547 /// value. This is intended as a cheap, non-recursive check. 548 ConstantRange computeConstantRange(const Value *V, bool ForSigned, 549 bool UseInstrInfo = true, 550 AssumptionCache *AC = nullptr, 551 const Instruction *CtxI = nullptr, 552 const DominatorTree *DT = nullptr, 553 unsigned Depth = 0); 554 555 /// Return true if this function can prove that the instruction I will 556 /// always transfer execution to one of its successors (including the next 557 /// instruction that follows within a basic block). E.g. this is not 558 /// guaranteed for function calls that could loop infinitely. 559 /// 560 /// In other words, this function returns false for instructions that may 561 /// transfer execution or fail to transfer execution in a way that is not 562 /// captured in the CFG nor in the sequence of instructions within a basic 563 /// block. 564 /// 565 /// Undefined behavior is assumed not to happen, so e.g. division is 566 /// guaranteed to transfer execution to the following instruction even 567 /// though division by zero might cause undefined behavior. 568 bool isGuaranteedToTransferExecutionToSuccessor(const Instruction *I); 569 570 /// Returns true if this block does not contain a potential implicit exit. 571 /// This is equivelent to saying that all instructions within the basic block 572 /// are guaranteed to transfer execution to their successor within the basic 573 /// block. This has the same assumptions w.r.t. undefined behavior as the 574 /// instruction variant of this function. 575 bool isGuaranteedToTransferExecutionToSuccessor(const BasicBlock *BB); 576 577 /// Return true if every instruction in the range (Begin, End) is 578 /// guaranteed to transfer execution to its static successor. \p ScanLimit 579 /// bounds the search to avoid scanning huge blocks. 580 bool isGuaranteedToTransferExecutionToSuccessor( 581 BasicBlock::const_iterator Begin, BasicBlock::const_iterator End, 582 unsigned ScanLimit = 32); 583 584 /// Same as previous, but with range expressed via iterator_range. 585 bool isGuaranteedToTransferExecutionToSuccessor( 586 iterator_range<BasicBlock::const_iterator> Range, 587 unsigned ScanLimit = 32); 588 589 /// Return true if this function can prove that the instruction I 590 /// is executed for every iteration of the loop L. 591 /// 592 /// Note that this currently only considers the loop header. 593 bool isGuaranteedToExecuteForEveryIteration(const Instruction *I, 594 const Loop *L); 595 596 /// Return true if I yields poison or raises UB if any of its operands is 597 /// poison. 598 /// Formally, given I = `r = op v1 v2 .. vN`, propagatesPoison returns true 599 /// if, for all i, r is evaluated to poison or op raises UB if vi = poison. 600 /// If vi is a vector or an aggregate and r is a single value, any poison 601 /// element in vi should make r poison or raise UB. 602 /// To filter out operands that raise UB on poison, you can use 603 /// getGuaranteedNonPoisonOp. 604 bool propagatesPoison(const Operator *I); 605 606 /// Insert operands of I into Ops such that I will trigger undefined behavior 607 /// if I is executed and that operand has a poison value. 608 void getGuaranteedNonPoisonOps(const Instruction *I, 609 SmallPtrSetImpl<const Value *> &Ops); 610 /// Insert operands of I into Ops such that I will trigger undefined behavior 611 /// if I is executed and that operand is not a well-defined value 612 /// (i.e. has undef bits or poison). 613 void getGuaranteedWellDefinedOps(const Instruction *I, 614 SmallPtrSetImpl<const Value *> &Ops); 615 616 /// Return true if the given instruction must trigger undefined behavior 617 /// when I is executed with any operands which appear in KnownPoison holding 618 /// a poison value at the point of execution. 619 bool mustTriggerUB(const Instruction *I, 620 const SmallSet<const Value *, 16>& KnownPoison); 621 622 /// Return true if this function can prove that if Inst is executed 623 /// and yields a poison value or undef bits, then that will trigger 624 /// undefined behavior. 625 /// 626 /// Note that this currently only considers the basic block that is 627 /// the parent of Inst. 628 bool programUndefinedIfUndefOrPoison(const Instruction *Inst); 629 bool programUndefinedIfPoison(const Instruction *Inst); 630 631 /// canCreateUndefOrPoison returns true if Op can create undef or poison from 632 /// non-undef & non-poison operands. 633 /// For vectors, canCreateUndefOrPoison returns true if there is potential 634 /// poison or undef in any element of the result when vectors without 635 /// undef/poison poison are given as operands. 636 /// For example, given `Op = shl <2 x i32> %x, <0, 32>`, this function returns 637 /// true. If Op raises immediate UB but never creates poison or undef 638 /// (e.g. sdiv I, 0), canCreatePoison returns false. 639 /// 640 /// \p ConsiderFlags controls whether poison producing flags on the 641 /// instruction are considered. This can be used to see if the instruction 642 /// could still introduce undef or poison even without poison generating flags 643 /// which might be on the instruction. (i.e. could the result of 644 /// Op->dropPoisonGeneratingFlags() still create poison or undef) 645 /// 646 /// canCreatePoison returns true if Op can create poison from non-poison 647 /// operands. 648 bool canCreateUndefOrPoison(const Operator *Op, bool ConsiderFlags = true); 649 bool canCreatePoison(const Operator *Op, bool ConsiderFlags = true); 650 651 /// Return true if V is poison given that ValAssumedPoison is already poison. 652 /// For example, if ValAssumedPoison is `icmp X, 10` and V is `icmp X, 5`, 653 /// impliesPoison returns true. 654 bool impliesPoison(const Value *ValAssumedPoison, const Value *V); 655 656 /// Return true if this function can prove that V does not have undef bits 657 /// and is never poison. If V is an aggregate value or vector, check whether 658 /// all elements (except padding) are not undef or poison. 659 /// Note that this is different from canCreateUndefOrPoison because the 660 /// function assumes Op's operands are not poison/undef. 661 /// 662 /// If CtxI and DT are specified this method performs flow-sensitive analysis 663 /// and returns true if it is guaranteed to be never undef or poison 664 /// immediately before the CtxI. 665 bool isGuaranteedNotToBeUndefOrPoison(const Value *V, 666 AssumptionCache *AC = nullptr, 667 const Instruction *CtxI = nullptr, 668 const DominatorTree *DT = nullptr, 669 unsigned Depth = 0); 670 bool isGuaranteedNotToBePoison(const Value *V, AssumptionCache *AC = nullptr, 671 const Instruction *CtxI = nullptr, 672 const DominatorTree *DT = nullptr, 673 unsigned Depth = 0); 674 675 /// Specific patterns of select instructions we can match. 676 enum SelectPatternFlavor { 677 SPF_UNKNOWN = 0, 678 SPF_SMIN, /// Signed minimum 679 SPF_UMIN, /// Unsigned minimum 680 SPF_SMAX, /// Signed maximum 681 SPF_UMAX, /// Unsigned maximum 682 SPF_FMINNUM, /// Floating point minnum 683 SPF_FMAXNUM, /// Floating point maxnum 684 SPF_ABS, /// Absolute value 685 SPF_NABS /// Negated absolute value 686 }; 687 688 /// Behavior when a floating point min/max is given one NaN and one 689 /// non-NaN as input. 690 enum SelectPatternNaNBehavior { 691 SPNB_NA = 0, /// NaN behavior not applicable. 692 SPNB_RETURNS_NAN, /// Given one NaN input, returns the NaN. 693 SPNB_RETURNS_OTHER, /// Given one NaN input, returns the non-NaN. 694 SPNB_RETURNS_ANY /// Given one NaN input, can return either (or 695 /// it has been determined that no operands can 696 /// be NaN). 697 }; 698 699 struct SelectPatternResult { 700 SelectPatternFlavor Flavor; 701 SelectPatternNaNBehavior NaNBehavior; /// Only applicable if Flavor is 702 /// SPF_FMINNUM or SPF_FMAXNUM. 703 bool Ordered; /// When implementing this min/max pattern as 704 /// fcmp; select, does the fcmp have to be 705 /// ordered? 706 707 /// Return true if \p SPF is a min or a max pattern. 708 static bool isMinOrMax(SelectPatternFlavor SPF) { 709 return SPF != SPF_UNKNOWN && SPF != SPF_ABS && SPF != SPF_NABS; 710 } 711 }; 712 713 /// Pattern match integer [SU]MIN, [SU]MAX and ABS idioms, returning the kind 714 /// and providing the out parameter results if we successfully match. 715 /// 716 /// For ABS/NABS, LHS will be set to the input to the abs idiom. RHS will be 717 /// the negation instruction from the idiom. 718 /// 719 /// If CastOp is not nullptr, also match MIN/MAX idioms where the type does 720 /// not match that of the original select. If this is the case, the cast 721 /// operation (one of Trunc,SExt,Zext) that must be done to transform the 722 /// type of LHS and RHS into the type of V is returned in CastOp. 723 /// 724 /// For example: 725 /// %1 = icmp slt i32 %a, i32 4 726 /// %2 = sext i32 %a to i64 727 /// %3 = select i1 %1, i64 %2, i64 4 728 /// 729 /// -> LHS = %a, RHS = i32 4, *CastOp = Instruction::SExt 730 /// 731 SelectPatternResult matchSelectPattern(Value *V, Value *&LHS, Value *&RHS, 732 Instruction::CastOps *CastOp = nullptr, 733 unsigned Depth = 0); 734 735 inline SelectPatternResult 736 matchSelectPattern(const Value *V, const Value *&LHS, const Value *&RHS) { 737 Value *L = const_cast<Value *>(LHS); 738 Value *R = const_cast<Value *>(RHS); 739 auto Result = matchSelectPattern(const_cast<Value *>(V), L, R); 740 LHS = L; 741 RHS = R; 742 return Result; 743 } 744 745 /// Determine the pattern that a select with the given compare as its 746 /// predicate and given values as its true/false operands would match. 747 SelectPatternResult matchDecomposedSelectPattern( 748 CmpInst *CmpI, Value *TrueVal, Value *FalseVal, Value *&LHS, Value *&RHS, 749 Instruction::CastOps *CastOp = nullptr, unsigned Depth = 0); 750 751 /// Return the canonical comparison predicate for the specified 752 /// minimum/maximum flavor. 753 CmpInst::Predicate getMinMaxPred(SelectPatternFlavor SPF, 754 bool Ordered = false); 755 756 /// Return the inverse minimum/maximum flavor of the specified flavor. 757 /// For example, signed minimum is the inverse of signed maximum. 758 SelectPatternFlavor getInverseMinMaxFlavor(SelectPatternFlavor SPF); 759 760 Intrinsic::ID getInverseMinMaxIntrinsic(Intrinsic::ID MinMaxID); 761 762 /// Return the canonical inverse comparison predicate for the specified 763 /// minimum/maximum flavor. 764 CmpInst::Predicate getInverseMinMaxPred(SelectPatternFlavor SPF); 765 766 /// Return the minimum or maximum constant value for the specified integer 767 /// min/max flavor and type. 768 APInt getMinMaxLimit(SelectPatternFlavor SPF, unsigned BitWidth); 769 770 /// Check if the values in \p VL are select instructions that can be converted 771 /// to a min or max (vector) intrinsic. Returns the intrinsic ID, if such a 772 /// conversion is possible, together with a bool indicating whether all select 773 /// conditions are only used by the selects. Otherwise return 774 /// Intrinsic::not_intrinsic. 775 std::pair<Intrinsic::ID, bool> 776 canConvertToMinOrMaxIntrinsic(ArrayRef<Value *> VL); 777 778 /// Attempt to match a simple first order recurrence cycle of the form: 779 /// %iv = phi Ty [%Start, %Entry], [%Inc, %backedge] 780 /// %inc = binop %iv, %step 781 /// OR 782 /// %iv = phi Ty [%Start, %Entry], [%Inc, %backedge] 783 /// %inc = binop %step, %iv 784 /// 785 /// A first order recurrence is a formula with the form: X_n = f(X_(n-1)) 786 /// 787 /// A couple of notes on subtleties in that definition: 788 /// * The Step does not have to be loop invariant. In math terms, it can 789 /// be a free variable. We allow recurrences with both constant and 790 /// variable coefficients. Callers may wish to filter cases where Step 791 /// does not dominate P. 792 /// * For non-commutative operators, we will match both forms. This 793 /// results in some odd recurrence structures. Callers may wish to filter 794 /// out recurrences where the phi is not the LHS of the returned operator. 795 /// * Because of the structure matched, the caller can assume as a post 796 /// condition of the match the presence of a Loop with P's parent as it's 797 /// header *except* in unreachable code. (Dominance decays in unreachable 798 /// code.) 799 /// 800 /// NOTE: This is intentional simple. If you want the ability to analyze 801 /// non-trivial loop conditons, see ScalarEvolution instead. 802 bool matchSimpleRecurrence(const PHINode *P, BinaryOperator *&BO, 803 Value *&Start, Value *&Step); 804 805 /// Analogous to the above, but starting from the binary operator 806 bool matchSimpleRecurrence(const BinaryOperator *I, PHINode *&P, 807 Value *&Start, Value *&Step); 808 809 /// Return true if RHS is known to be implied true by LHS. Return false if 810 /// RHS is known to be implied false by LHS. Otherwise, return None if no 811 /// implication can be made. 812 /// A & B must be i1 (boolean) values or a vector of such values. Note that 813 /// the truth table for implication is the same as <=u on i1 values (but not 814 /// <=s!). The truth table for both is: 815 /// | T | F (B) 816 /// T | T | F 817 /// F | T | T 818 /// (A) 819 Optional<bool> isImpliedCondition(const Value *LHS, const Value *RHS, 820 const DataLayout &DL, bool LHSIsTrue = true, 821 unsigned Depth = 0); 822 Optional<bool> isImpliedCondition(const Value *LHS, 823 CmpInst::Predicate RHSPred, 824 const Value *RHSOp0, const Value *RHSOp1, 825 const DataLayout &DL, bool LHSIsTrue = true, 826 unsigned Depth = 0); 827 828 /// Return the boolean condition value in the context of the given instruction 829 /// if it is known based on dominating conditions. 830 Optional<bool> isImpliedByDomCondition(const Value *Cond, 831 const Instruction *ContextI, 832 const DataLayout &DL); 833 Optional<bool> isImpliedByDomCondition(CmpInst::Predicate Pred, 834 const Value *LHS, const Value *RHS, 835 const Instruction *ContextI, 836 const DataLayout &DL); 837 838 /// If Ptr1 is provably equal to Ptr2 plus a constant offset, return that 839 /// offset. For example, Ptr1 might be &A[42], and Ptr2 might be &A[40]. In 840 /// this case offset would be -8. 841 Optional<int64_t> isPointerOffset(const Value *Ptr1, const Value *Ptr2, 842 const DataLayout &DL); 843 } // end namespace llvm 844 845 #endif // LLVM_ANALYSIS_VALUETRACKING_H 846