1//===- AliasSetTracker.cpp - Alias Sets Tracker implementation-------------===//
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 implements the AliasSetTracker and AliasSet classes.
10//
11//===----------------------------------------------------------------------===//
12
13#include "llvm/Analysis/AliasSetTracker.h"
14#include "llvm/ADT/SetVector.h"
15#include "llvm/ADT/StringExtras.h"
16#include "llvm/Analysis/AliasAnalysis.h"
17#include "llvm/Analysis/GuardUtils.h"
18#include "llvm/Analysis/MemoryLocation.h"
19#include "llvm/Config/llvm-config.h"
20#include "llvm/IR/Function.h"
21#include "llvm/IR/InstIterator.h"
22#include "llvm/IR/Instructions.h"
23#include "llvm/IR/IntrinsicInst.h"
24#include "llvm/IR/PassManager.h"
25#include "llvm/IR/PatternMatch.h"
26#include "llvm/IR/Value.h"
27#include "llvm/InitializePasses.h"
28#include "llvm/Pass.h"
29#include "llvm/Support/AtomicOrdering.h"
30#include "llvm/Support/CommandLine.h"
31#include "llvm/Support/Compiler.h"
32#include "llvm/Support/Debug.h"
33#include "llvm/Support/ErrorHandling.h"
34#include "llvm/Support/raw_ostream.h"
35
36using namespace llvm;
37
38static cl::opt<unsigned> SaturationThreshold(
39 "alias-set-saturation-threshold", cl::Hidden, cl::init(Val: 250),
40 cl::desc("The maximum total number of memory locations alias "
41 "sets may contain before degradation"));
42
43/// mergeSetIn - Merge the specified alias set into this alias set.
44void AliasSet::mergeSetIn(AliasSet &AS, AliasSetTracker &AST,
45 BatchAAResults &BatchAA) {
46 assert(!AS.Forward && "Alias set is already forwarding!");
47 assert(!Forward && "This set is a forwarding set!!");
48
49 // Update the alias and access types of this set...
50 Access |= AS.Access;
51 Alias |= AS.Alias;
52
53 if (Alias == SetMustAlias) {
54 // Check that these two merged sets really are must aliases. If we cannot
55 // find a must-alias pair between them, this set becomes a may alias.
56 if (!any_of(Range&: MemoryLocs, P: [&](const MemoryLocation &MemLoc) {
57 return any_of(Range&: AS.MemoryLocs, P: [&](const MemoryLocation &ASMemLoc) {
58 return BatchAA.isMustAlias(LocA: MemLoc, LocB: ASMemLoc);
59 });
60 }))
61 Alias = SetMayAlias;
62 }
63
64 // Merge the list of constituent memory locations...
65 if (MemoryLocs.empty()) {
66 std::swap(LHS&: MemoryLocs, RHS&: AS.MemoryLocs);
67 } else {
68 append_range(C&: MemoryLocs, R&: AS.MemoryLocs);
69 AS.MemoryLocs.clear();
70 }
71
72 bool ASHadUnknownInsts = !AS.UnknownInsts.empty();
73 if (UnknownInsts.empty()) { // Merge call sites...
74 if (ASHadUnknownInsts) {
75 std::swap(x&: UnknownInsts, y&: AS.UnknownInsts);
76 addRef();
77 }
78 } else if (ASHadUnknownInsts) {
79 llvm::append_range(C&: UnknownInsts, R&: AS.UnknownInsts);
80 AS.UnknownInsts.clear();
81 }
82
83 AS.Forward = this; // Forward across AS now...
84 addRef(); // AS is now pointing to us...
85
86 if (ASHadUnknownInsts)
87 AS.dropRef(AST);
88}
89
90void AliasSetTracker::removeAliasSet(AliasSet *AS) {
91 if (AliasSet *Fwd = AS->Forward) {
92 Fwd->dropRef(AST&: *this);
93 AS->Forward = nullptr;
94 } else // Update TotalAliasSetSize only if not forwarding.
95 TotalAliasSetSize -= AS->size();
96
97 AliasSets.erase(IT: AS);
98 // If we've removed the saturated alias set, set saturated marker back to
99 // nullptr and ensure this tracker is empty.
100 if (AS == AliasAnyAS) {
101 AliasAnyAS = nullptr;
102 assert(AliasSets.empty() && "Tracker not empty");
103 }
104}
105
106void AliasSet::removeFromTracker(AliasSetTracker &AST) {
107 assert(RefCount == 0 && "Cannot remove non-dead alias set from tracker!");
108 AST.removeAliasSet(AS: this);
109}
110
111void AliasSet::addMemoryLocation(AliasSetTracker &AST,
112 const MemoryLocation &MemLoc,
113 bool KnownMustAlias) {
114 if (isMustAlias() && !KnownMustAlias) {
115 // If we cannot find a must-alias with any of the existing MemoryLocs, we
116 // must downgrade to may-alias.
117 if (!any_of(Range&: MemoryLocs, P: [&](const MemoryLocation &ASMemLoc) {
118 return AST.getAliasAnalysis().isMustAlias(LocA: MemLoc, LocB: ASMemLoc);
119 }))
120 Alias = SetMayAlias;
121 }
122
123 // Add it to the end of the list...
124 MemoryLocs.push_back(Elt: MemLoc);
125
126 AST.TotalAliasSetSize++;
127}
128
129void AliasSet::addUnknownInst(Instruction *I, BatchAAResults &AA) {
130 if (UnknownInsts.empty())
131 addRef();
132 UnknownInsts.emplace_back(args&: I);
133
134 // Guards are marked as modifying memory for control flow modelling purposes,
135 // but don't actually modify any specific memory location.
136 using namespace PatternMatch;
137 bool MayWriteMemory = I->mayWriteToMemory() && !isGuard(I) &&
138 !(I->use_empty() && match(I, m_Intrinsic<Intrinsic::invariant_start>()));
139 if (!MayWriteMemory) {
140 Alias = SetMayAlias;
141 Access |= RefAccess;
142 return;
143 }
144
145 // FIXME: This should use mod/ref information to make this not suck so bad
146 Alias = SetMayAlias;
147 Access = ModRefAccess;
148}
149
150/// aliasesMemoryLocation - If the specified memory location "may" (or must)
151/// alias one of the members in the set return the appropriate AliasResult.
152/// Otherwise return NoAlias.
153///
154AliasResult AliasSet::aliasesMemoryLocation(const MemoryLocation &MemLoc,
155 BatchAAResults &AA) const {
156 if (AliasAny)
157 return AliasResult::MayAlias;
158
159 // Check all of the memory locations in the set...
160 for (const auto &ASMemLoc : MemoryLocs) {
161 AliasResult AR = AA.alias(LocA: MemLoc, LocB: ASMemLoc);
162 if (AR != AliasResult::NoAlias)
163 return AR;
164 }
165
166 // Check the unknown instructions...
167 for (Instruction *Inst : UnknownInsts)
168 if (isModOrRefSet(MRI: AA.getModRefInfo(I: Inst, OptLoc: MemLoc)))
169 return AliasResult::MayAlias;
170
171 return AliasResult::NoAlias;
172}
173
174ModRefInfo AliasSet::aliasesUnknownInst(const Instruction *Inst,
175 BatchAAResults &AA) const {
176
177 if (AliasAny)
178 return ModRefInfo::ModRef;
179
180 if (!Inst->mayReadOrWriteMemory())
181 return ModRefInfo::NoModRef;
182
183 for (Instruction *UnknownInst : UnknownInsts) {
184 const auto *C1 = dyn_cast<CallBase>(Val: UnknownInst);
185 const auto *C2 = dyn_cast<CallBase>(Val: Inst);
186 if (!C1 || !C2 || isModOrRefSet(MRI: AA.getModRefInfo(I: C1, Call2: C2)) ||
187 isModOrRefSet(MRI: AA.getModRefInfo(I: C2, Call2: C1))) {
188 // TODO: Could be more precise, but not really useful right now.
189 return ModRefInfo::ModRef;
190 }
191 }
192
193 ModRefInfo MR = ModRefInfo::NoModRef;
194 for (const auto &ASMemLoc : MemoryLocs) {
195 MR |= AA.getModRefInfo(I: Inst, OptLoc: ASMemLoc);
196 if (isModAndRefSet(MRI: MR))
197 return MR;
198 }
199
200 return MR;
201}
202
203AliasSet::PointerVector AliasSet::getPointers() const {
204 SmallSetVector<const Value *, 8> Pointers;
205 for (const MemoryLocation &MemLoc : MemoryLocs)
206 Pointers.insert(X: MemLoc.Ptr);
207 return Pointers.takeVector();
208}
209
210void AliasSetTracker::clear() {
211 PointerMap.clear();
212 AliasSets.clear();
213}
214
215/// mergeAliasSetsForMemoryLocation - Given a memory location, merge all alias
216/// sets that may alias it. Return the unified set, or nullptr if no aliasing
217/// set was found. A known existing alias set for the pointer value of the
218/// memory location can be passed in (or nullptr if not available). MustAliasAll
219/// is updated to true/false if the memory location is found to MustAlias all
220/// the sets it merged.
221AliasSet *AliasSetTracker::mergeAliasSetsForMemoryLocation(
222 const MemoryLocation &MemLoc, AliasSet *PtrAS, bool &MustAliasAll) {
223 AliasSet *FoundSet = nullptr;
224 MustAliasAll = true;
225 for (AliasSet &AS : llvm::make_early_inc_range(Range&: *this)) {
226 if (AS.Forward)
227 continue;
228
229 // An alias set that already contains a memory location with the same
230 // pointer value is directly assumed to MustAlias; we bypass the AA query in
231 // this case.
232 // Note: it is not guaranteed that AA would always provide the same result;
233 // a known exception are undef pointer values, where alias(undef, undef) is
234 // NoAlias, while we treat it as MustAlias.
235 if (&AS != PtrAS) {
236 AliasResult AR = AS.aliasesMemoryLocation(MemLoc, AA);
237 if (AR == AliasResult::NoAlias)
238 continue;
239
240 if (AR != AliasResult::MustAlias)
241 MustAliasAll = false;
242 }
243
244 if (!FoundSet) {
245 // If this is the first alias set ptr can go into, remember it.
246 FoundSet = &AS;
247 } else {
248 // Otherwise, we must merge the sets.
249 FoundSet->mergeSetIn(AS, AST&: *this, BatchAA&: AA);
250 }
251 }
252
253 return FoundSet;
254}
255
256AliasSet *AliasSetTracker::findAliasSetForUnknownInst(Instruction *Inst) {
257 AliasSet *FoundSet = nullptr;
258 for (AliasSet &AS : llvm::make_early_inc_range(Range&: *this)) {
259 if (AS.Forward || !isModOrRefSet(MRI: AS.aliasesUnknownInst(Inst, AA)))
260 continue;
261 if (!FoundSet) {
262 // If this is the first alias set ptr can go into, remember it.
263 FoundSet = &AS;
264 } else {
265 // Otherwise, we must merge the sets.
266 FoundSet->mergeSetIn(AS, AST&: *this, BatchAA&: AA);
267 }
268 }
269 return FoundSet;
270}
271
272AliasSet &AliasSetTracker::getAliasSetFor(const MemoryLocation &MemLoc) {
273 // The alias sets are indexed with a map from the memory locations' pointer
274 // values. If the memory location is already registered, we can find it in the
275 // alias set associated with its pointer.
276 AliasSet *&MapEntry = PointerMap[MemLoc.Ptr];
277 if (MapEntry) {
278 collapseForwardingIn(AS&: MapEntry);
279 if (is_contained(Range&: MapEntry->MemoryLocs, Element: MemLoc))
280 return *MapEntry;
281 }
282
283 AliasSet *AS;
284 bool MustAliasAll = false;
285 if (AliasAnyAS) {
286 // At this point, the AST is saturated, so we only have one active alias
287 // set. That means we already know which alias set we want to return, and
288 // just need to add the memory location to that set to keep the data
289 // structure consistent.
290 // This, of course, means that we will never need a merge here.
291 AS = AliasAnyAS;
292 } else if (AliasSet *AliasAS = mergeAliasSetsForMemoryLocation(
293 MemLoc, PtrAS: MapEntry, MustAliasAll)) {
294 // Add it to the alias set it aliases.
295 AS = AliasAS;
296 } else {
297 // Otherwise create a new alias set to hold the new memory location.
298 AliasSets.push_back(val: AS = new AliasSet());
299 MustAliasAll = true;
300 }
301
302 // Register memory location in selected alias set.
303 AS->addMemoryLocation(AST&: *this, MemLoc, KnownMustAlias: MustAliasAll);
304 // Register selected alias set in pointer map (or ensure it is consistent with
305 // earlier map entry after taking into account new merging).
306 if (MapEntry) {
307 collapseForwardingIn(AS&: MapEntry);
308 assert(MapEntry == AS && "Memory locations with same pointer value cannot "
309 "be in different alias sets");
310 } else {
311 AS->addRef();
312 MapEntry = AS;
313 }
314 return *AS;
315}
316
317void AliasSetTracker::add(const MemoryLocation &Loc) {
318 addMemoryLocation(Loc, E: AliasSet::NoAccess);
319}
320
321void AliasSetTracker::add(LoadInst *LI) {
322 if (isStrongerThanMonotonic(AO: LI->getOrdering()))
323 return addUnknown(I: LI);
324 addMemoryLocation(Loc: MemoryLocation::get(LI), E: AliasSet::RefAccess);
325}
326
327void AliasSetTracker::add(StoreInst *SI) {
328 if (isStrongerThanMonotonic(AO: SI->getOrdering()))
329 return addUnknown(I: SI);
330 addMemoryLocation(Loc: MemoryLocation::get(SI), E: AliasSet::ModAccess);
331}
332
333void AliasSetTracker::add(VAArgInst *VAAI) {
334 addMemoryLocation(Loc: MemoryLocation::get(VI: VAAI), E: AliasSet::ModRefAccess);
335}
336
337void AliasSetTracker::add(AnyMemSetInst *MSI) {
338 addMemoryLocation(Loc: MemoryLocation::getForDest(MI: MSI), E: AliasSet::ModAccess);
339}
340
341void AliasSetTracker::add(AnyMemTransferInst *MTI) {
342 addMemoryLocation(Loc: MemoryLocation::getForDest(MI: MTI), E: AliasSet::ModAccess);
343 addMemoryLocation(Loc: MemoryLocation::getForSource(MTI), E: AliasSet::RefAccess);
344}
345
346void AliasSetTracker::addUnknown(Instruction *Inst) {
347 if (isa<DbgInfoIntrinsic>(Val: Inst))
348 return; // Ignore DbgInfo Intrinsics.
349
350 if (auto *II = dyn_cast<IntrinsicInst>(Val: Inst)) {
351 // These intrinsics will show up as affecting memory, but they are just
352 // markers.
353 switch (II->getIntrinsicID()) {
354 default:
355 break;
356 // FIXME: Add lifetime/invariant intrinsics (See: PR30807).
357 case Intrinsic::allow_runtime_check:
358 case Intrinsic::allow_ubsan_check:
359 case Intrinsic::assume:
360 case Intrinsic::experimental_noalias_scope_decl:
361 case Intrinsic::sideeffect:
362 case Intrinsic::pseudoprobe:
363 return;
364 }
365 }
366 if (!Inst->mayReadOrWriteMemory())
367 return; // doesn't alias anything
368
369 if (AliasSet *AS = findAliasSetForUnknownInst(Inst)) {
370 AS->addUnknownInst(I: Inst, AA);
371 return;
372 }
373 AliasSets.push_back(val: new AliasSet());
374 AliasSets.back().addUnknownInst(I: Inst, AA);
375}
376
377void AliasSetTracker::add(Instruction *I) {
378 // Dispatch to one of the other add methods.
379 if (LoadInst *LI = dyn_cast<LoadInst>(Val: I))
380 return add(LI);
381 if (StoreInst *SI = dyn_cast<StoreInst>(Val: I))
382 return add(SI);
383 if (VAArgInst *VAAI = dyn_cast<VAArgInst>(Val: I))
384 return add(VAAI);
385 if (AnyMemSetInst *MSI = dyn_cast<AnyMemSetInst>(Val: I))
386 return add(MSI);
387 if (AnyMemTransferInst *MTI = dyn_cast<AnyMemTransferInst>(Val: I))
388 return add(MTI);
389
390 // Handle all calls with known mod/ref sets genericall
391 if (auto *Call = dyn_cast<CallBase>(Val: I))
392 if (Call->onlyAccessesArgMemory()) {
393 auto getAccessFromModRef = [](ModRefInfo MRI) {
394 if (isRefSet(MRI) && isModSet(MRI))
395 return AliasSet::ModRefAccess;
396 else if (isModSet(MRI))
397 return AliasSet::ModAccess;
398 else if (isRefSet(MRI))
399 return AliasSet::RefAccess;
400 else
401 return AliasSet::NoAccess;
402 };
403
404 ModRefInfo CallMask = AA.getMemoryEffects(Call).getModRef();
405
406 // Some intrinsics are marked as modifying memory for control flow
407 // modelling purposes, but don't actually modify any specific memory
408 // location.
409 using namespace PatternMatch;
410 if (Call->use_empty() &&
411 match(Call, m_Intrinsic<Intrinsic::invariant_start>()))
412 CallMask &= ModRefInfo::Ref;
413
414 for (auto IdxArgPair : enumerate(First: Call->args())) {
415 int ArgIdx = IdxArgPair.index();
416 const Value *Arg = IdxArgPair.value();
417 if (!Arg->getType()->isPointerTy())
418 continue;
419 MemoryLocation ArgLoc =
420 MemoryLocation::getForArgument(Call, ArgIdx, TLI: nullptr);
421 ModRefInfo ArgMask = AA.getArgModRefInfo(Call, ArgIdx);
422 ArgMask &= CallMask;
423 if (!isNoModRef(MRI: ArgMask))
424 addMemoryLocation(Loc: ArgLoc, E: getAccessFromModRef(ArgMask));
425 }
426 return;
427 }
428
429 return addUnknown(Inst: I);
430}
431
432void AliasSetTracker::add(BasicBlock &BB) {
433 for (auto &I : BB)
434 add(I: &I);
435}
436
437void AliasSetTracker::add(const AliasSetTracker &AST) {
438 assert(&AA == &AST.AA &&
439 "Merging AliasSetTracker objects with different Alias Analyses!");
440
441 // Loop over all of the alias sets in AST, adding the members contained
442 // therein into the current alias sets. This can cause alias sets to be
443 // merged together in the current AST.
444 for (const AliasSet &AS : AST) {
445 if (AS.Forward)
446 continue; // Ignore forwarding alias sets
447
448 // If there are any call sites in the alias set, add them to this AST.
449 for (Instruction *Inst : AS.UnknownInsts)
450 add(I: Inst);
451
452 // Loop over all of the memory locations in this alias set.
453 for (const MemoryLocation &ASMemLoc : AS.MemoryLocs)
454 addMemoryLocation(Loc: ASMemLoc, E: (AliasSet::AccessLattice)AS.Access);
455 }
456}
457
458AliasSet &AliasSetTracker::mergeAllAliasSets() {
459 assert(!AliasAnyAS && (TotalAliasSetSize > SaturationThreshold) &&
460 "Full merge should happen once, when the saturation threshold is "
461 "reached");
462
463 // Collect all alias sets, so that we can drop references with impunity
464 // without worrying about iterator invalidation.
465 std::vector<AliasSet *> ASVector;
466 ASVector.reserve(n: SaturationThreshold);
467 for (AliasSet &AS : *this)
468 ASVector.push_back(x: &AS);
469
470 // Copy all instructions and memory locations into a new set, and forward all
471 // other sets to it.
472 AliasSets.push_back(val: new AliasSet());
473 AliasAnyAS = &AliasSets.back();
474 AliasAnyAS->Alias = AliasSet::SetMayAlias;
475 AliasAnyAS->Access = AliasSet::ModRefAccess;
476 AliasAnyAS->AliasAny = true;
477
478 for (auto *Cur : ASVector) {
479 // If Cur was already forwarding, just forward to the new AS instead.
480 AliasSet *FwdTo = Cur->Forward;
481 if (FwdTo) {
482 Cur->Forward = AliasAnyAS;
483 AliasAnyAS->addRef();
484 FwdTo->dropRef(AST&: *this);
485 continue;
486 }
487
488 // Otherwise, perform the actual merge.
489 AliasAnyAS->mergeSetIn(AS&: *Cur, AST&: *this, BatchAA&: AA);
490 }
491
492 return *AliasAnyAS;
493}
494
495AliasSet &AliasSetTracker::addMemoryLocation(MemoryLocation Loc,
496 AliasSet::AccessLattice E) {
497 AliasSet &AS = getAliasSetFor(MemLoc: Loc);
498 AS.Access |= E;
499
500 if (!AliasAnyAS && (TotalAliasSetSize > SaturationThreshold)) {
501 // The AST is now saturated. From here on, we conservatively consider all
502 // elements to alias each-other.
503 return mergeAllAliasSets();
504 }
505
506 return AS;
507}
508
509//===----------------------------------------------------------------------===//
510// AliasSet/AliasSetTracker Printing Support
511//===----------------------------------------------------------------------===//
512
513void AliasSet::print(raw_ostream &OS) const {
514 OS << " AliasSet[" << (const void*)this << ", " << RefCount << "] ";
515 OS << (Alias == SetMustAlias ? "must" : "may") << " alias, ";
516 switch (Access) {
517 case NoAccess: OS << "No access "; break;
518 case RefAccess: OS << "Ref "; break;
519 case ModAccess: OS << "Mod "; break;
520 case ModRefAccess: OS << "Mod/Ref "; break;
521 default: llvm_unreachable("Bad value for Access!");
522 }
523 if (Forward)
524 OS << " forwarding to " << (void*)Forward;
525
526 if (!MemoryLocs.empty()) {
527 ListSeparator LS;
528 OS << "Memory locations: ";
529 for (const MemoryLocation &MemLoc : MemoryLocs) {
530 OS << LS;
531 MemLoc.Ptr->printAsOperand(O&: OS << "(");
532 if (MemLoc.Size == LocationSize::afterPointer())
533 OS << ", unknown after)";
534 else if (MemLoc.Size == LocationSize::beforeOrAfterPointer())
535 OS << ", unknown before-or-after)";
536 else
537 OS << ", " << MemLoc.Size << ")";
538 }
539 }
540 if (!UnknownInsts.empty()) {
541 ListSeparator LS;
542 OS << "\n " << UnknownInsts.size() << " Unknown instructions: ";
543 for (Instruction *I : UnknownInsts) {
544 OS << LS;
545 if (I->hasName())
546 I->printAsOperand(O&: OS);
547 else
548 I->print(O&: OS);
549 }
550 }
551 OS << "\n";
552}
553
554void AliasSetTracker::print(raw_ostream &OS) const {
555 OS << "Alias Set Tracker: " << AliasSets.size();
556 if (AliasAnyAS)
557 OS << " (Saturated)";
558 OS << " alias sets for " << PointerMap.size() << " pointer values.\n";
559 for (const AliasSet &AS : *this)
560 AS.print(OS);
561 OS << "\n";
562}
563
564#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
565LLVM_DUMP_METHOD void AliasSet::dump() const { print(OS&: dbgs()); }
566LLVM_DUMP_METHOD void AliasSetTracker::dump() const { print(OS&: dbgs()); }
567#endif
568
569//===----------------------------------------------------------------------===//
570// AliasSetPrinter Pass
571//===----------------------------------------------------------------------===//
572
573AliasSetsPrinterPass::AliasSetsPrinterPass(raw_ostream &OS) : OS(OS) {}
574
575PreservedAnalyses AliasSetsPrinterPass::run(Function &F,
576 FunctionAnalysisManager &AM) {
577 auto &AA = AM.getResult<AAManager>(IR&: F);
578 BatchAAResults BatchAA(AA);
579 AliasSetTracker Tracker(BatchAA);
580 OS << "Alias sets for function '" << F.getName() << "':\n";
581 for (Instruction &I : instructions(F))
582 Tracker.add(I: &I);
583 Tracker.print(OS);
584 return PreservedAnalyses::all();
585}
586

source code of llvm/lib/Analysis/AliasSetTracker.cpp