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