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/CallSite.h" 21 #include "llvm/IR/Constants.h" 22 #include "llvm/IR/DataLayout.h" 23 #include "llvm/IR/Instruction.h" 24 #include "llvm/IR/Intrinsics.h" 25 #include <cassert> 26 #include <cstdint> 27 28 namespace llvm { 29 30 class AddOperator; 31 class APInt; 32 class AssumptionCache; 33 class DominatorTree; 34 class GEPOperator; 35 class IntrinsicInst; 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 /// Determine which bits of V are known to be either zero or one and return 47 /// them in the KnownZero/KnownOne bit sets. 48 /// 49 /// This function is defined on values with integer type, values with pointer 50 /// type, and vectors of integers. In the case 51 /// where V is a vector, the known zero and known one values are the 52 /// same width as the vector element, and the bit is set only if it is true 53 /// for all of the elements in the vector. 54 void computeKnownBits(const Value *V, KnownBits &Known, 55 const DataLayout &DL, unsigned Depth = 0, 56 AssumptionCache *AC = nullptr, 57 const Instruction *CxtI = nullptr, 58 const DominatorTree *DT = nullptr, 59 OptimizationRemarkEmitter *ORE = nullptr, 60 bool UseInstrInfo = true); 61 62 /// Returns the known bits rather than passing by reference. 63 KnownBits computeKnownBits(const Value *V, const DataLayout &DL, 64 unsigned Depth = 0, AssumptionCache *AC = nullptr, 65 const Instruction *CxtI = nullptr, 66 const DominatorTree *DT = nullptr, 67 OptimizationRemarkEmitter *ORE = nullptr, 68 bool UseInstrInfo = true); 69 70 /// Compute known bits from the range metadata. 71 /// \p KnownZero the set of bits that are known to be zero 72 /// \p KnownOne the set of bits that are known to be one 73 void computeKnownBitsFromRangeMetadata(const MDNode &Ranges, 74 KnownBits &Known); 75 76 /// Return true if LHS and RHS have no common bits set. 77 bool haveNoCommonBitsSet(const Value *LHS, const Value *RHS, 78 const DataLayout &DL, 79 AssumptionCache *AC = nullptr, 80 const Instruction *CxtI = nullptr, 81 const DominatorTree *DT = nullptr, 82 bool UseInstrInfo = true); 83 84 /// Return true if the given value is known to have exactly one bit set when 85 /// defined. For vectors return true if every element is known to be a power 86 /// of two when defined. Supports values with integer or pointer type and 87 /// vectors of integers. If 'OrZero' is set, then return true if the given 88 /// value is either a power of two or zero. 89 bool isKnownToBeAPowerOfTwo(const Value *V, const DataLayout &DL, 90 bool OrZero = false, unsigned Depth = 0, 91 AssumptionCache *AC = nullptr, 92 const Instruction *CxtI = nullptr, 93 const DominatorTree *DT = nullptr, 94 bool UseInstrInfo = true); 95 96 bool isOnlyUsedInZeroEqualityComparison(const Instruction *CxtI); 97 98 /// Return true if the given value is known to be non-zero when defined. For 99 /// vectors, return true if every element is known to be non-zero when 100 /// defined. For pointers, if the context instruction and dominator tree are 101 /// specified, perform context-sensitive analysis and return true if the 102 /// pointer couldn't possibly be null at the specified instruction. 103 /// Supports values with integer or pointer type and vectors of integers. 104 bool isKnownNonZero(const Value *V, const DataLayout &DL, unsigned Depth = 0, 105 AssumptionCache *AC = nullptr, 106 const Instruction *CxtI = nullptr, 107 const DominatorTree *DT = nullptr, 108 bool UseInstrInfo = true); 109 110 /// Return true if the two given values are negation. 111 /// Currently can recoginze Value pair: 112 /// 1: <X, Y> if X = sub (0, Y) or Y = sub (0, X) 113 /// 2: <X, Y> if X = sub (A, B) and Y = sub (B, A) 114 bool isKnownNegation(const Value *X, const Value *Y, bool NeedNSW = false); 115 116 /// Returns true if the give value is known to be non-negative. 117 bool isKnownNonNegative(const Value *V, const DataLayout &DL, 118 unsigned Depth = 0, 119 AssumptionCache *AC = nullptr, 120 const Instruction *CxtI = nullptr, 121 const DominatorTree *DT = nullptr, 122 bool UseInstrInfo = true); 123 124 /// Returns true if the given value is known be positive (i.e. non-negative 125 /// and non-zero). 126 bool isKnownPositive(const Value *V, const DataLayout &DL, unsigned Depth = 0, 127 AssumptionCache *AC = nullptr, 128 const Instruction *CxtI = nullptr, 129 const DominatorTree *DT = nullptr, 130 bool UseInstrInfo = true); 131 132 /// Returns true if the given value is known be negative (i.e. non-positive 133 /// and non-zero). 134 bool isKnownNegative(const Value *V, const DataLayout &DL, unsigned Depth = 0, 135 AssumptionCache *AC = nullptr, 136 const Instruction *CxtI = nullptr, 137 const DominatorTree *DT = nullptr, 138 bool UseInstrInfo = true); 139 140 /// Return true if the given values are known to be non-equal when defined. 141 /// Supports scalar integer types only. 142 bool isKnownNonEqual(const Value *V1, const Value *V2, const DataLayout &DL, 143 AssumptionCache *AC = nullptr, 144 const Instruction *CxtI = nullptr, 145 const DominatorTree *DT = nullptr, 146 bool UseInstrInfo = true); 147 148 /// Return true if 'V & Mask' is known to be zero. We use this predicate to 149 /// simplify operations downstream. Mask is known to be zero for bits that V 150 /// cannot have. 151 /// 152 /// This function is defined on values with integer type, values with pointer 153 /// type, and vectors of integers. In the case 154 /// where V is a vector, the mask, known zero, and known one values are the 155 /// same width as the vector element, and the bit is set only if it is true 156 /// for all of the elements in the vector. 157 bool MaskedValueIsZero(const Value *V, const APInt &Mask, 158 const DataLayout &DL, 159 unsigned Depth = 0, AssumptionCache *AC = nullptr, 160 const Instruction *CxtI = nullptr, 161 const DominatorTree *DT = nullptr, 162 bool UseInstrInfo = true); 163 164 /// Return the number of times the sign bit of the register is replicated into 165 /// the other bits. We know that at least 1 bit is always equal to the sign 166 /// bit (itself), but other cases can give us information. For example, 167 /// immediately after an "ashr X, 2", we know that the top 3 bits are all 168 /// equal to each other, so we return 3. For vectors, return the number of 169 /// sign bits for the vector element with the mininum number of known sign 170 /// bits. 171 unsigned ComputeNumSignBits(const Value *Op, const DataLayout &DL, 172 unsigned Depth = 0, AssumptionCache *AC = nullptr, 173 const Instruction *CxtI = nullptr, 174 const DominatorTree *DT = nullptr, 175 bool UseInstrInfo = true); 176 177 /// This function computes the integer multiple of Base that equals V. If 178 /// successful, it returns true and returns the multiple in Multiple. If 179 /// unsuccessful, it returns false. Also, if V can be simplified to an 180 /// integer, then the simplified V is returned in Val. Look through sext only 181 /// if LookThroughSExt=true. 182 bool ComputeMultiple(Value *V, unsigned Base, Value *&Multiple, 183 bool LookThroughSExt = false, 184 unsigned Depth = 0); 185 186 /// Map a call instruction to an intrinsic ID. Libcalls which have equivalent 187 /// intrinsics are treated as-if they were intrinsics. 188 Intrinsic::ID getIntrinsicForCallSite(ImmutableCallSite ICS, 189 const TargetLibraryInfo *TLI); 190 191 /// Return true if we can prove that the specified FP value is never equal to 192 /// -0.0. 193 bool CannotBeNegativeZero(const Value *V, const TargetLibraryInfo *TLI, 194 unsigned Depth = 0); 195 196 /// Return true if we can prove that the specified FP value is either NaN or 197 /// never less than -0.0. 198 /// 199 /// NaN --> true 200 /// +0 --> true 201 /// -0 --> true 202 /// x > +0 --> true 203 /// x < -0 --> false 204 bool CannotBeOrderedLessThanZero(const Value *V, const TargetLibraryInfo *TLI); 205 206 /// Return true if the floating-point scalar value is not an infinity or if 207 /// the floating-point vector value has no infinities. Return false if a value 208 /// could ever be infinity. 209 bool isKnownNeverInfinity(const Value *V, const TargetLibraryInfo *TLI, 210 unsigned Depth = 0); 211 212 /// Return true if the floating-point scalar value is not a NaN or if the 213 /// floating-point vector value has no NaN elements. Return false if a value 214 /// could ever be NaN. 215 bool isKnownNeverNaN(const Value *V, const TargetLibraryInfo *TLI, 216 unsigned Depth = 0); 217 218 /// Return true if we can prove that the specified FP value's sign bit is 0. 219 /// 220 /// NaN --> true/false (depending on the NaN's sign bit) 221 /// +0 --> true 222 /// -0 --> false 223 /// x > +0 --> true 224 /// x < -0 --> false 225 bool SignBitMustBeZero(const Value *V, const TargetLibraryInfo *TLI); 226 227 /// If the specified value can be set by repeating the same byte in memory, 228 /// return the i8 value that it is represented with. This is true for all i8 229 /// values obviously, but is also true for i32 0, i32 -1, i16 0xF0F0, double 230 /// 0.0 etc. If the value can't be handled with a repeated byte store (e.g. 231 /// i16 0x1234), return null. If the value is entirely undef and padding, 232 /// return undef. 233 Value *isBytewiseValue(Value *V, const DataLayout &DL); 234 235 /// Given an aggregate and an sequence of indices, see if the scalar value 236 /// indexed is already around as a register, for example if it were inserted 237 /// directly into the aggregate. 238 /// 239 /// If InsertBefore is not null, this function will duplicate (modified) 240 /// insertvalues when a part of a nested struct is extracted. 241 Value *FindInsertedValue(Value *V, 242 ArrayRef<unsigned> idx_range, 243 Instruction *InsertBefore = nullptr); 244 245 /// Analyze the specified pointer to see if it can be expressed as a base 246 /// pointer plus a constant offset. Return the base and offset to the caller. 247 /// 248 /// This is a wrapper around Value::stripAndAccumulateConstantOffsets that 249 /// creates and later unpacks the required APInt. 250 inline Value *GetPointerBaseWithConstantOffset(Value *Ptr, int64_t &Offset, 251 const DataLayout &DL, 252 bool AllowNonInbounds = true) { 253 APInt OffsetAPInt(DL.getIndexTypeSizeInBits(Ptr->getType()), 0); 254 Value *Base = 255 Ptr->stripAndAccumulateConstantOffsets(DL, OffsetAPInt, AllowNonInbounds); 256 257 Offset = OffsetAPInt.getSExtValue(); 258 return Base; 259 } 260 inline const Value * 261 GetPointerBaseWithConstantOffset(const Value *Ptr, int64_t &Offset, 262 const DataLayout &DL, 263 bool AllowNonInbounds = true) { 264 return GetPointerBaseWithConstantOffset(const_cast<Value *>(Ptr), Offset, DL, 265 AllowNonInbounds); 266 } 267 268 /// Returns true if the GEP is based on a pointer to a string (array of 269 // \p CharSize integers) and is indexing into this string. 270 bool isGEPBasedOnPointerToString(const GEPOperator *GEP, 271 unsigned CharSize = 8); 272 273 /// Represents offset+length into a ConstantDataArray. 274 struct ConstantDataArraySlice { 275 /// ConstantDataArray pointer. nullptr indicates a zeroinitializer (a valid 276 /// initializer, it just doesn't fit the ConstantDataArray interface). 277 const ConstantDataArray *Array; 278 279 /// Slice starts at this Offset. 280 uint64_t Offset; 281 282 /// Length of the slice. 283 uint64_t Length; 284 285 /// Moves the Offset and adjusts Length accordingly. moveConstantDataArraySlice286 void move(uint64_t Delta) { 287 assert(Delta < Length); 288 Offset += Delta; 289 Length -= Delta; 290 } 291 292 /// Convenience accessor for elements in the slice. 293 uint64_t operator[](unsigned I) const { 294 return Array==nullptr ? 0 : Array->getElementAsInteger(I + Offset); 295 } 296 }; 297 298 /// Returns true if the value \p V is a pointer into a ConstantDataArray. 299 /// If successful \p Slice will point to a ConstantDataArray info object 300 /// with an appropriate offset. 301 bool getConstantDataArrayInfo(const Value *V, ConstantDataArraySlice &Slice, 302 unsigned ElementSize, uint64_t Offset = 0); 303 304 /// This function computes the length of a null-terminated C string pointed to 305 /// by V. If successful, it returns true and returns the string in Str. If 306 /// unsuccessful, it returns false. This does not include the trailing null 307 /// character by default. If TrimAtNul is set to false, then this returns any 308 /// trailing null characters as well as any other characters that come after 309 /// it. 310 bool getConstantStringInfo(const Value *V, StringRef &Str, 311 uint64_t Offset = 0, bool TrimAtNul = true); 312 313 /// If we can compute the length of the string pointed to by the specified 314 /// pointer, return 'len+1'. If we can't, return 0. 315 uint64_t GetStringLength(const Value *V, unsigned CharSize = 8); 316 317 /// This function returns call pointer argument that is considered the same by 318 /// aliasing rules. You CAN'T use it to replace one value with another. If 319 /// \p MustPreserveNullness is true, the call must preserve the nullness of 320 /// the pointer. 321 const Value *getArgumentAliasingToReturnedPointer(const CallBase *Call, 322 bool MustPreserveNullness); 323 inline Value * getArgumentAliasingToReturnedPointer(CallBase * Call,bool MustPreserveNullness)324 getArgumentAliasingToReturnedPointer(CallBase *Call, 325 bool MustPreserveNullness) { 326 return const_cast<Value *>(getArgumentAliasingToReturnedPointer( 327 const_cast<const CallBase *>(Call), MustPreserveNullness)); 328 } 329 330 /// {launder,strip}.invariant.group returns pointer that aliases its argument, 331 /// and it only captures pointer by returning it. 332 /// These intrinsics are not marked as nocapture, because returning is 333 /// considered as capture. The arguments are not marked as returned neither, 334 /// because it would make it useless. If \p MustPreserveNullness is true, 335 /// the intrinsic must preserve the nullness of the pointer. 336 bool isIntrinsicReturningPointerAliasingArgumentWithoutCapturing( 337 const CallBase *Call, bool MustPreserveNullness); 338 339 /// This method strips off any GEP address adjustments and pointer casts from 340 /// the specified value, returning the original object being addressed. Note 341 /// that the returned value has pointer type if the specified value does. If 342 /// the MaxLookup value is non-zero, it limits the number of instructions to 343 /// be stripped off. 344 Value *GetUnderlyingObject(Value *V, const DataLayout &DL, 345 unsigned MaxLookup = 6); 346 inline const Value *GetUnderlyingObject(const Value *V, const DataLayout &DL, 347 unsigned MaxLookup = 6) { 348 return GetUnderlyingObject(const_cast<Value *>(V), DL, MaxLookup); 349 } 350 351 /// This method is similar to GetUnderlyingObject except that it can 352 /// look through phi and select instructions and return multiple objects. 353 /// 354 /// If LoopInfo is passed, loop phis are further analyzed. If a pointer 355 /// accesses different objects in each iteration, we don't look through the 356 /// phi node. E.g. consider this loop nest: 357 /// 358 /// int **A; 359 /// for (i) 360 /// for (j) { 361 /// A[i][j] = A[i-1][j] * B[j] 362 /// } 363 /// 364 /// This is transformed by Load-PRE to stash away A[i] for the next iteration 365 /// of the outer loop: 366 /// 367 /// Curr = A[0]; // Prev_0 368 /// for (i: 1..N) { 369 /// Prev = Curr; // Prev = PHI (Prev_0, Curr) 370 /// Curr = A[i]; 371 /// for (j: 0..N) { 372 /// Curr[j] = Prev[j] * B[j] 373 /// } 374 /// } 375 /// 376 /// Since A[i] and A[i-1] are independent pointers, getUnderlyingObjects 377 /// should not assume that Curr and Prev share the same underlying object thus 378 /// it shouldn't look through the phi above. 379 void GetUnderlyingObjects(const Value *V, 380 SmallVectorImpl<const Value *> &Objects, 381 const DataLayout &DL, LoopInfo *LI = nullptr, 382 unsigned MaxLookup = 6); 383 384 /// This is a wrapper around GetUnderlyingObjects and adds support for basic 385 /// ptrtoint+arithmetic+inttoptr sequences. 386 bool getUnderlyingObjectsForCodeGen(const Value *V, 387 SmallVectorImpl<Value *> &Objects, 388 const DataLayout &DL); 389 390 /// Return true if the only users of this pointer are lifetime markers. 391 bool onlyUsedByLifetimeMarkers(const Value *V); 392 393 /// Return true if speculation of the given load must be suppressed to avoid 394 /// ordering or interfering with an active sanitizer. If not suppressed, 395 /// dereferenceability and alignment must be proven separately. Note: This 396 /// is only needed for raw reasoning; if you use the interface below 397 /// (isSafeToSpeculativelyExecute), this is handled internally. 398 bool mustSuppressSpeculation(const LoadInst &LI); 399 400 /// Return true if the instruction does not have any effects besides 401 /// calculating the result and does not have undefined behavior. 402 /// 403 /// This method never returns true for an instruction that returns true for 404 /// mayHaveSideEffects; however, this method also does some other checks in 405 /// addition. It checks for undefined behavior, like dividing by zero or 406 /// loading from an invalid pointer (but not for undefined results, like a 407 /// shift with a shift amount larger than the width of the result). It checks 408 /// for malloc and alloca because speculatively executing them might cause a 409 /// memory leak. It also returns false for instructions related to control 410 /// flow, specifically terminators and PHI nodes. 411 /// 412 /// If the CtxI is specified this method performs context-sensitive analysis 413 /// and returns true if it is safe to execute the instruction immediately 414 /// before the CtxI. 415 /// 416 /// If the CtxI is NOT specified this method only looks at the instruction 417 /// itself and its operands, so if this method returns true, it is safe to 418 /// move the instruction as long as the correct dominance relationships for 419 /// the operands and users hold. 420 /// 421 /// This method can return true for instructions that read memory; 422 /// for such instructions, moving them may change the resulting value. 423 bool isSafeToSpeculativelyExecute(const Value *V, 424 const Instruction *CtxI = nullptr, 425 const DominatorTree *DT = nullptr); 426 427 /// Returns true if the result or effects of the given instructions \p I 428 /// depend on or influence global memory. 429 /// Memory dependence arises for example if the instruction reads from 430 /// memory or may produce effects or undefined behaviour. Memory dependent 431 /// instructions generally cannot be reorderd with respect to other memory 432 /// dependent instructions or moved into non-dominated basic blocks. 433 /// Instructions which just compute a value based on the values of their 434 /// operands are not memory dependent. 435 bool mayBeMemoryDependent(const Instruction &I); 436 437 /// Return true if it is an intrinsic that cannot be speculated but also 438 /// cannot trap. 439 bool isAssumeLikeIntrinsic(const Instruction *I); 440 441 /// Return true if it is valid to use the assumptions provided by an 442 /// assume intrinsic, I, at the point in the control-flow identified by the 443 /// context instruction, CxtI. 444 bool isValidAssumeForContext(const Instruction *I, const Instruction *CxtI, 445 const DominatorTree *DT = nullptr); 446 447 enum class OverflowResult { 448 /// Always overflows in the direction of signed/unsigned min value. 449 AlwaysOverflowsLow, 450 /// Always overflows in the direction of signed/unsigned max value. 451 AlwaysOverflowsHigh, 452 /// May or may not overflow. 453 MayOverflow, 454 /// Never overflows. 455 NeverOverflows, 456 }; 457 458 OverflowResult computeOverflowForUnsignedMul(const Value *LHS, 459 const Value *RHS, 460 const DataLayout &DL, 461 AssumptionCache *AC, 462 const Instruction *CxtI, 463 const DominatorTree *DT, 464 bool UseInstrInfo = true); 465 OverflowResult computeOverflowForSignedMul(const Value *LHS, const Value *RHS, 466 const DataLayout &DL, 467 AssumptionCache *AC, 468 const Instruction *CxtI, 469 const DominatorTree *DT, 470 bool UseInstrInfo = true); 471 OverflowResult computeOverflowForUnsignedAdd(const Value *LHS, 472 const Value *RHS, 473 const DataLayout &DL, 474 AssumptionCache *AC, 475 const Instruction *CxtI, 476 const DominatorTree *DT, 477 bool UseInstrInfo = true); 478 OverflowResult computeOverflowForSignedAdd(const Value *LHS, const Value *RHS, 479 const DataLayout &DL, 480 AssumptionCache *AC = nullptr, 481 const Instruction *CxtI = nullptr, 482 const DominatorTree *DT = nullptr); 483 /// This version also leverages the sign bit of Add if known. 484 OverflowResult computeOverflowForSignedAdd(const AddOperator *Add, 485 const DataLayout &DL, 486 AssumptionCache *AC = nullptr, 487 const Instruction *CxtI = nullptr, 488 const DominatorTree *DT = nullptr); 489 OverflowResult computeOverflowForUnsignedSub(const Value *LHS, const Value *RHS, 490 const DataLayout &DL, 491 AssumptionCache *AC, 492 const Instruction *CxtI, 493 const DominatorTree *DT); 494 OverflowResult computeOverflowForSignedSub(const Value *LHS, const Value *RHS, 495 const DataLayout &DL, 496 AssumptionCache *AC, 497 const Instruction *CxtI, 498 const DominatorTree *DT); 499 500 /// Returns true if the arithmetic part of the \p WO 's result is 501 /// used only along the paths control dependent on the computation 502 /// not overflowing, \p WO being an <op>.with.overflow intrinsic. 503 bool isOverflowIntrinsicNoWrap(const WithOverflowInst *WO, 504 const DominatorTree &DT); 505 506 507 /// Determine the possible constant range of an integer or vector of integer 508 /// value. This is intended as a cheap, non-recursive check. 509 ConstantRange computeConstantRange(const Value *V, bool UseInstrInfo = true); 510 511 /// Return true if this function can prove that the instruction I will 512 /// always transfer execution to one of its successors (including the next 513 /// instruction that follows within a basic block). E.g. this is not 514 /// guaranteed for function calls that could loop infinitely. 515 /// 516 /// In other words, this function returns false for instructions that may 517 /// transfer execution or fail to transfer execution in a way that is not 518 /// captured in the CFG nor in the sequence of instructions within a basic 519 /// block. 520 /// 521 /// Undefined behavior is assumed not to happen, so e.g. division is 522 /// guaranteed to transfer execution to the following instruction even 523 /// though division by zero might cause undefined behavior. 524 bool isGuaranteedToTransferExecutionToSuccessor(const Instruction *I); 525 526 /// Returns true if this block does not contain a potential implicit exit. 527 /// This is equivelent to saying that all instructions within the basic block 528 /// are guaranteed to transfer execution to their successor within the basic 529 /// block. This has the same assumptions w.r.t. undefined behavior as the 530 /// instruction variant of this function. 531 bool isGuaranteedToTransferExecutionToSuccessor(const BasicBlock *BB); 532 533 /// Return true if this function can prove that the instruction I 534 /// is executed for every iteration of the loop L. 535 /// 536 /// Note that this currently only considers the loop header. 537 bool isGuaranteedToExecuteForEveryIteration(const Instruction *I, 538 const Loop *L); 539 540 /// Return true if this function can prove that I is guaranteed to yield 541 /// full-poison (all bits poison) if at least one of its operands are 542 /// full-poison (all bits poison). 543 /// 544 /// The exact rules for how poison propagates through instructions have 545 /// not been settled as of 2015-07-10, so this function is conservative 546 /// and only considers poison to be propagated in uncontroversial 547 /// cases. There is no attempt to track values that may be only partially 548 /// poison. 549 bool propagatesFullPoison(const Instruction *I); 550 551 /// Return either nullptr or an operand of I such that I will trigger 552 /// undefined behavior if I is executed and that operand has a full-poison 553 /// value (all bits poison). 554 const Value *getGuaranteedNonFullPoisonOp(const Instruction *I); 555 556 /// Return true if the given instruction must trigger undefined behavior. 557 /// when I is executed with any operands which appear in KnownPoison holding 558 /// a full-poison value at the point of execution. 559 bool mustTriggerUB(const Instruction *I, 560 const SmallSet<const Value *, 16>& KnownPoison); 561 562 /// Return true if this function can prove that if PoisonI is executed 563 /// and yields a full-poison value (all bits poison), then that will 564 /// trigger undefined behavior. 565 /// 566 /// Note that this currently only considers the basic block that is 567 /// the parent of I. 568 bool programUndefinedIfFullPoison(const Instruction *PoisonI); 569 570 /// Return true if this function can prove that V is never undef value 571 /// or poison value. 572 bool isGuaranteedNotToBeUndefOrPoison(const Value *V); 573 574 /// Specific patterns of select instructions we can match. 575 enum SelectPatternFlavor { 576 SPF_UNKNOWN = 0, 577 SPF_SMIN, /// Signed minimum 578 SPF_UMIN, /// Unsigned minimum 579 SPF_SMAX, /// Signed maximum 580 SPF_UMAX, /// Unsigned maximum 581 SPF_FMINNUM, /// Floating point minnum 582 SPF_FMAXNUM, /// Floating point maxnum 583 SPF_ABS, /// Absolute value 584 SPF_NABS /// Negated absolute value 585 }; 586 587 /// Behavior when a floating point min/max is given one NaN and one 588 /// non-NaN as input. 589 enum SelectPatternNaNBehavior { 590 SPNB_NA = 0, /// NaN behavior not applicable. 591 SPNB_RETURNS_NAN, /// Given one NaN input, returns the NaN. 592 SPNB_RETURNS_OTHER, /// Given one NaN input, returns the non-NaN. 593 SPNB_RETURNS_ANY /// Given one NaN input, can return either (or 594 /// it has been determined that no operands can 595 /// be NaN). 596 }; 597 598 struct SelectPatternResult { 599 SelectPatternFlavor Flavor; 600 SelectPatternNaNBehavior NaNBehavior; /// Only applicable if Flavor is 601 /// SPF_FMINNUM or SPF_FMAXNUM. 602 bool Ordered; /// When implementing this min/max pattern as 603 /// fcmp; select, does the fcmp have to be 604 /// ordered? 605 606 /// Return true if \p SPF is a min or a max pattern. isMinOrMaxSelectPatternResult607 static bool isMinOrMax(SelectPatternFlavor SPF) { 608 return SPF != SPF_UNKNOWN && SPF != SPF_ABS && SPF != SPF_NABS; 609 } 610 }; 611 612 /// Pattern match integer [SU]MIN, [SU]MAX and ABS idioms, returning the kind 613 /// and providing the out parameter results if we successfully match. 614 /// 615 /// For ABS/NABS, LHS will be set to the input to the abs idiom. RHS will be 616 /// the negation instruction from the idiom. 617 /// 618 /// If CastOp is not nullptr, also match MIN/MAX idioms where the type does 619 /// not match that of the original select. If this is the case, the cast 620 /// operation (one of Trunc,SExt,Zext) that must be done to transform the 621 /// type of LHS and RHS into the type of V is returned in CastOp. 622 /// 623 /// For example: 624 /// %1 = icmp slt i32 %a, i32 4 625 /// %2 = sext i32 %a to i64 626 /// %3 = select i1 %1, i64 %2, i64 4 627 /// 628 /// -> LHS = %a, RHS = i32 4, *CastOp = Instruction::SExt 629 /// 630 SelectPatternResult matchSelectPattern(Value *V, Value *&LHS, Value *&RHS, 631 Instruction::CastOps *CastOp = nullptr, 632 unsigned Depth = 0); 633 634 inline SelectPatternResult matchSelectPattern(const Value * V,const Value * & LHS,const Value * & RHS)635 matchSelectPattern(const Value *V, const Value *&LHS, const Value *&RHS) { 636 Value *L = const_cast<Value *>(LHS); 637 Value *R = const_cast<Value *>(RHS); 638 auto Result = matchSelectPattern(const_cast<Value *>(V), L, R); 639 LHS = L; 640 RHS = R; 641 return Result; 642 } 643 644 /// Determine the pattern that a select with the given compare as its 645 /// predicate and given values as its true/false operands would match. 646 SelectPatternResult matchDecomposedSelectPattern( 647 CmpInst *CmpI, Value *TrueVal, Value *FalseVal, Value *&LHS, Value *&RHS, 648 Instruction::CastOps *CastOp = nullptr, unsigned Depth = 0); 649 650 /// Return the canonical comparison predicate for the specified 651 /// minimum/maximum flavor. 652 CmpInst::Predicate getMinMaxPred(SelectPatternFlavor SPF, 653 bool Ordered = false); 654 655 /// Return the inverse minimum/maximum flavor of the specified flavor. 656 /// For example, signed minimum is the inverse of signed maximum. 657 SelectPatternFlavor getInverseMinMaxFlavor(SelectPatternFlavor SPF); 658 659 /// Return the canonical inverse comparison predicate for the specified 660 /// minimum/maximum flavor. 661 CmpInst::Predicate getInverseMinMaxPred(SelectPatternFlavor SPF); 662 663 /// Return true if RHS is known to be implied true by LHS. Return false if 664 /// RHS is known to be implied false by LHS. Otherwise, return None if no 665 /// implication can be made. 666 /// A & B must be i1 (boolean) values or a vector of such values. Note that 667 /// the truth table for implication is the same as <=u on i1 values (but not 668 /// <=s!). The truth table for both is: 669 /// | T | F (B) 670 /// T | T | F 671 /// F | T | T 672 /// (A) 673 Optional<bool> isImpliedCondition(const Value *LHS, const Value *RHS, 674 const DataLayout &DL, bool LHSIsTrue = true, 675 unsigned Depth = 0); 676 677 /// Return the boolean condition value in the context of the given instruction 678 /// if it is known based on dominating conditions. 679 Optional<bool> isImpliedByDomCondition(const Value *Cond, 680 const Instruction *ContextI, 681 const DataLayout &DL); 682 683 /// If Ptr1 is provably equal to Ptr2 plus a constant offset, return that 684 /// offset. For example, Ptr1 might be &A[42], and Ptr2 might be &A[40]. In 685 /// this case offset would be -8. 686 Optional<int64_t> isPointerOffset(const Value *Ptr1, const Value *Ptr2, 687 const DataLayout &DL); 688 } // end namespace llvm 689 690 #endif // LLVM_ANALYSIS_VALUETRACKING_H 691