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