LLVM 19.0.0git
TypeBasedAliasAnalysis.cpp
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1//===- TypeBasedAliasAnalysis.cpp - Type-Based Alias Analysis -------------===//
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 defines the TypeBasedAliasAnalysis pass, which implements
10// metadata-based TBAA.
11//
12// In LLVM IR, memory does not have types, so LLVM's own type system is not
13// suitable for doing TBAA. Instead, metadata is added to the IR to describe
14// a type system of a higher level language. This can be used to implement
15// typical C/C++ TBAA, but it can also be used to implement custom alias
16// analysis behavior for other languages.
17//
18// We now support two types of metadata format: scalar TBAA and struct-path
19// aware TBAA. After all testing cases are upgraded to use struct-path aware
20// TBAA and we can auto-upgrade existing bc files, the support for scalar TBAA
21// can be dropped.
22//
23// The scalar TBAA metadata format is very simple. TBAA MDNodes have up to
24// three fields, e.g.:
25// !0 = !{ !"an example type tree" }
26// !1 = !{ !"int", !0 }
27// !2 = !{ !"float", !0 }
28// !3 = !{ !"const float", !2, i64 1 }
29//
30// The first field is an identity field. It can be any value, usually
31// an MDString, which uniquely identifies the type. The most important
32// name in the tree is the name of the root node. Two trees with
33// different root node names are entirely disjoint, even if they
34// have leaves with common names.
35//
36// The second field identifies the type's parent node in the tree, or
37// is null or omitted for a root node. A type is considered to alias
38// all of its descendants and all of its ancestors in the tree. Also,
39// a type is considered to alias all types in other trees, so that
40// bitcode produced from multiple front-ends is handled conservatively.
41//
42// If the third field is present, it's an integer which if equal to 1
43// indicates that the type is "constant" (meaning pointsToConstantMemory
44// should return true; see
45// http://llvm.org/docs/AliasAnalysis.html#OtherItfs).
46//
47// With struct-path aware TBAA, the MDNodes attached to an instruction using
48// "!tbaa" are called path tag nodes.
49//
50// The path tag node has 4 fields with the last field being optional.
51//
52// The first field is the base type node, it can be a struct type node
53// or a scalar type node. The second field is the access type node, it
54// must be a scalar type node. The third field is the offset into the base type.
55// The last field has the same meaning as the last field of our scalar TBAA:
56// it's an integer which if equal to 1 indicates that the access is "constant".
57//
58// The struct type node has a name and a list of pairs, one pair for each member
59// of the struct. The first element of each pair is a type node (a struct type
60// node or a scalar type node), specifying the type of the member, the second
61// element of each pair is the offset of the member.
62//
63// Given an example
64// typedef struct {
65// short s;
66// } A;
67// typedef struct {
68// uint16_t s;
69// A a;
70// } B;
71//
72// For an access to B.a.s, we attach !5 (a path tag node) to the load/store
73// instruction. The base type is !4 (struct B), the access type is !2 (scalar
74// type short) and the offset is 4.
75//
76// !0 = !{!"Simple C/C++ TBAA"}
77// !1 = !{!"omnipotent char", !0} // Scalar type node
78// !2 = !{!"short", !1} // Scalar type node
79// !3 = !{!"A", !2, i64 0} // Struct type node
80// !4 = !{!"B", !2, i64 0, !3, i64 4}
81// // Struct type node
82// !5 = !{!4, !2, i64 4} // Path tag node
83//
84// The struct type nodes and the scalar type nodes form a type DAG.
85// Root (!0)
86// char (!1) -- edge to Root
87// short (!2) -- edge to char
88// A (!3) -- edge with offset 0 to short
89// B (!4) -- edge with offset 0 to short and edge with offset 4 to A
90//
91// To check if two tags (tagX and tagY) can alias, we start from the base type
92// of tagX, follow the edge with the correct offset in the type DAG and adjust
93// the offset until we reach the base type of tagY or until we reach the Root
94// node.
95// If we reach the base type of tagY, compare the adjusted offset with
96// offset of tagY, return Alias if the offsets are the same, return NoAlias
97// otherwise.
98// If we reach the Root node, perform the above starting from base type of tagY
99// to see if we reach base type of tagX.
100//
101// If they have different roots, they're part of different potentially
102// unrelated type systems, so we return Alias to be conservative.
103// If neither node is an ancestor of the other and they have the same root,
104// then we say NoAlias.
105//
106//===----------------------------------------------------------------------===//
107
109#include "llvm/ADT/SetVector.h"
112#include "llvm/IR/Constants.h"
113#include "llvm/IR/DerivedTypes.h"
114#include "llvm/IR/InstrTypes.h"
115#include "llvm/IR/LLVMContext.h"
116#include "llvm/IR/Metadata.h"
118#include "llvm/Pass.h"
119#include "llvm/Support/Casting.h"
122#include <cassert>
123#include <cstdint>
124
125using namespace llvm;
126
127// A handy option for disabling TBAA functionality. The same effect can also be
128// achieved by stripping the !tbaa tags from IR, but this option is sometimes
129// more convenient.
130static cl::opt<bool> EnableTBAA("enable-tbaa", cl::init(true), cl::Hidden);
131
132namespace {
133
134/// isNewFormatTypeNode - Return true iff the given type node is in the new
135/// size-aware format.
136static bool isNewFormatTypeNode(const MDNode *N) {
137 if (N->getNumOperands() < 3)
138 return false;
139 // In the old format the first operand is a string.
140 if (!isa<MDNode>(N->getOperand(0)))
141 return false;
142 return true;
143}
144
145/// This is a simple wrapper around an MDNode which provides a higher-level
146/// interface by hiding the details of how alias analysis information is encoded
147/// in its operands.
148template<typename MDNodeTy>
149class TBAANodeImpl {
150 MDNodeTy *Node = nullptr;
151
152public:
153 TBAANodeImpl() = default;
154 explicit TBAANodeImpl(MDNodeTy *N) : Node(N) {}
155
156 /// getNode - Get the MDNode for this TBAANode.
157 MDNodeTy *getNode() const { return Node; }
158
159 /// isNewFormat - Return true iff the wrapped type node is in the new
160 /// size-aware format.
161 bool isNewFormat() const { return isNewFormatTypeNode(Node); }
162
163 /// getParent - Get this TBAANode's Alias tree parent.
164 TBAANodeImpl<MDNodeTy> getParent() const {
165 if (isNewFormat())
166 return TBAANodeImpl(cast<MDNodeTy>(Node->getOperand(0)));
167
168 if (Node->getNumOperands() < 2)
169 return TBAANodeImpl<MDNodeTy>();
170 MDNodeTy *P = dyn_cast_or_null<MDNodeTy>(Node->getOperand(1));
171 if (!P)
172 return TBAANodeImpl<MDNodeTy>();
173 // Ok, this node has a valid parent. Return it.
174 return TBAANodeImpl<MDNodeTy>(P);
175 }
176
177 /// Test if this TBAANode represents a type for objects which are
178 /// not modified (by any means) in the context where this
179 /// AliasAnalysis is relevant.
180 bool isTypeImmutable() const {
181 if (Node->getNumOperands() < 3)
182 return false;
183 ConstantInt *CI = mdconst::dyn_extract<ConstantInt>(Node->getOperand(2));
184 if (!CI)
185 return false;
186 return CI->getValue()[0];
187 }
188};
189
190/// \name Specializations of \c TBAANodeImpl for const and non const qualified
191/// \c MDNode.
192/// @{
193using TBAANode = TBAANodeImpl<const MDNode>;
194using MutableTBAANode = TBAANodeImpl<MDNode>;
195/// @}
196
197/// This is a simple wrapper around an MDNode which provides a
198/// higher-level interface by hiding the details of how alias analysis
199/// information is encoded in its operands.
200template<typename MDNodeTy>
201class TBAAStructTagNodeImpl {
202 /// This node should be created with createTBAAAccessTag().
203 MDNodeTy *Node;
204
205public:
206 explicit TBAAStructTagNodeImpl(MDNodeTy *N) : Node(N) {}
207
208 /// Get the MDNode for this TBAAStructTagNode.
209 MDNodeTy *getNode() const { return Node; }
210
211 /// isNewFormat - Return true iff the wrapped access tag is in the new
212 /// size-aware format.
213 bool isNewFormat() const {
214 if (Node->getNumOperands() < 4)
215 return false;
216 if (MDNodeTy *AccessType = getAccessType())
217 if (!TBAANodeImpl<MDNodeTy>(AccessType).isNewFormat())
218 return false;
219 return true;
220 }
221
222 MDNodeTy *getBaseType() const {
223 return dyn_cast_or_null<MDNode>(Node->getOperand(0));
224 }
225
226 MDNodeTy *getAccessType() const {
227 return dyn_cast_or_null<MDNode>(Node->getOperand(1));
228 }
229
230 uint64_t getOffset() const {
231 return mdconst::extract<ConstantInt>(Node->getOperand(2))->getZExtValue();
232 }
233
234 uint64_t getSize() const {
235 if (!isNewFormat())
236 return UINT64_MAX;
237 return mdconst::extract<ConstantInt>(Node->getOperand(3))->getZExtValue();
238 }
239
240 /// Test if this TBAAStructTagNode represents a type for objects
241 /// which are not modified (by any means) in the context where this
242 /// AliasAnalysis is relevant.
243 bool isTypeImmutable() const {
244 unsigned OpNo = isNewFormat() ? 4 : 3;
245 if (Node->getNumOperands() < OpNo + 1)
246 return false;
247 ConstantInt *CI = mdconst::dyn_extract<ConstantInt>(Node->getOperand(OpNo));
248 if (!CI)
249 return false;
250 return CI->getValue()[0];
251 }
252};
253
254/// \name Specializations of \c TBAAStructTagNodeImpl for const and non const
255/// qualified \c MDNods.
256/// @{
257using TBAAStructTagNode = TBAAStructTagNodeImpl<const MDNode>;
258using MutableTBAAStructTagNode = TBAAStructTagNodeImpl<MDNode>;
259/// @}
260
261/// This is a simple wrapper around an MDNode which provides a
262/// higher-level interface by hiding the details of how alias analysis
263/// information is encoded in its operands.
264class TBAAStructTypeNode {
265 /// This node should be created with createTBAATypeNode().
266 const MDNode *Node = nullptr;
267
268public:
269 TBAAStructTypeNode() = default;
270 explicit TBAAStructTypeNode(const MDNode *N) : Node(N) {}
271
272 /// Get the MDNode for this TBAAStructTypeNode.
273 const MDNode *getNode() const { return Node; }
274
275 /// isNewFormat - Return true iff the wrapped type node is in the new
276 /// size-aware format.
277 bool isNewFormat() const { return isNewFormatTypeNode(Node); }
278
279 bool operator==(const TBAAStructTypeNode &Other) const {
280 return getNode() == Other.getNode();
281 }
282
283 /// getId - Return type identifier.
284 Metadata *getId() const {
285 return Node->getOperand(isNewFormat() ? 2 : 0);
286 }
287
288 unsigned getNumFields() const {
289 unsigned FirstFieldOpNo = isNewFormat() ? 3 : 1;
290 unsigned NumOpsPerField = isNewFormat() ? 3 : 2;
291 return (getNode()->getNumOperands() - FirstFieldOpNo) / NumOpsPerField;
292 }
293
294 TBAAStructTypeNode getFieldType(unsigned FieldIndex) const {
295 unsigned FirstFieldOpNo = isNewFormat() ? 3 : 1;
296 unsigned NumOpsPerField = isNewFormat() ? 3 : 2;
297 unsigned OpIndex = FirstFieldOpNo + FieldIndex * NumOpsPerField;
298 auto *TypeNode = cast<MDNode>(getNode()->getOperand(OpIndex));
299 return TBAAStructTypeNode(TypeNode);
300 }
301
302 /// Get this TBAAStructTypeNode's field in the type DAG with
303 /// given offset. Update the offset to be relative to the field type.
304 TBAAStructTypeNode getField(uint64_t &Offset) const {
305 bool NewFormat = isNewFormat();
306 const ArrayRef<MDOperand> Operands = Node->operands();
307 const unsigned NumOperands = Operands.size();
308
309 if (NewFormat) {
310 // New-format root and scalar type nodes have no fields.
311 if (NumOperands < 6)
312 return TBAAStructTypeNode();
313 } else {
314 // Parent can be omitted for the root node.
315 if (NumOperands < 2)
316 return TBAAStructTypeNode();
317
318 // Fast path for a scalar type node and a struct type node with a single
319 // field.
320 if (NumOperands <= 3) {
321 uint64_t Cur =
322 NumOperands == 2
323 ? 0
324 : mdconst::extract<ConstantInt>(Operands[2])->getZExtValue();
325 Offset -= Cur;
326 MDNode *P = dyn_cast_or_null<MDNode>(Operands[1]);
327 if (!P)
328 return TBAAStructTypeNode();
329 return TBAAStructTypeNode(P);
330 }
331 }
332
333 // Assume the offsets are in order. We return the previous field if
334 // the current offset is bigger than the given offset.
335 unsigned FirstFieldOpNo = NewFormat ? 3 : 1;
336 unsigned NumOpsPerField = NewFormat ? 3 : 2;
337 unsigned TheIdx = 0;
338
339 for (unsigned Idx = FirstFieldOpNo; Idx < NumOperands;
340 Idx += NumOpsPerField) {
341 uint64_t Cur =
342 mdconst::extract<ConstantInt>(Operands[Idx + 1])->getZExtValue();
343 if (Cur > Offset) {
344 assert(Idx >= FirstFieldOpNo + NumOpsPerField &&
345 "TBAAStructTypeNode::getField should have an offset match!");
346 TheIdx = Idx - NumOpsPerField;
347 break;
348 }
349 }
350 // Move along the last field.
351 if (TheIdx == 0)
352 TheIdx = NumOperands - NumOpsPerField;
353 uint64_t Cur =
354 mdconst::extract<ConstantInt>(Operands[TheIdx + 1])->getZExtValue();
355 Offset -= Cur;
356 MDNode *P = dyn_cast_or_null<MDNode>(Operands[TheIdx]);
357 if (!P)
358 return TBAAStructTypeNode();
359 return TBAAStructTypeNode(P);
360 }
361};
362
363} // end anonymous namespace
364
365/// Check the first operand of the tbaa tag node, if it is a MDNode, we treat
366/// it as struct-path aware TBAA format, otherwise, we treat it as scalar TBAA
367/// format.
368static bool isStructPathTBAA(const MDNode *MD) {
369 // Anonymous TBAA root starts with a MDNode and dragonegg uses it as
370 // a TBAA tag.
371 return isa<MDNode>(MD->getOperand(0)) && MD->getNumOperands() >= 3;
372}
373
375 const MemoryLocation &LocB,
376 AAQueryInfo &AAQI, const Instruction *) {
377 if (!EnableTBAA)
379
380 if (Aliases(LocA.AATags.TBAA, LocB.AATags.TBAA))
382
383 // Otherwise return a definitive result.
385}
386
388 AAQueryInfo &AAQI,
389 bool IgnoreLocals) {
390 if (!EnableTBAA)
391 return ModRefInfo::ModRef;
392
393 const MDNode *M = Loc.AATags.TBAA;
394 if (!M)
395 return ModRefInfo::ModRef;
396
397 // If this is an "immutable" type, we can assume the pointer is pointing
398 // to constant memory.
399 if ((!isStructPathTBAA(M) && TBAANode(M).isTypeImmutable()) ||
400 (isStructPathTBAA(M) && TBAAStructTagNode(M).isTypeImmutable()))
402
403 return ModRefInfo::ModRef;
404}
405
407 AAQueryInfo &AAQI) {
408 if (!EnableTBAA)
409 return MemoryEffects::unknown();
410
411 // If this is an "immutable" type, the access is not observable.
412 if (const MDNode *M = Call->getMetadata(LLVMContext::MD_tbaa))
413 if ((!isStructPathTBAA(M) && TBAANode(M).isTypeImmutable()) ||
414 (isStructPathTBAA(M) && TBAAStructTagNode(M).isTypeImmutable()))
415 return MemoryEffects::none();
416
417 return MemoryEffects::unknown();
418}
419
421 // Functions don't have metadata.
422 return MemoryEffects::unknown();
423}
424
426 const MemoryLocation &Loc,
427 AAQueryInfo &AAQI) {
428 if (!EnableTBAA)
429 return ModRefInfo::ModRef;
430
431 if (const MDNode *L = Loc.AATags.TBAA)
432 if (const MDNode *M = Call->getMetadata(LLVMContext::MD_tbaa))
433 if (!Aliases(L, M))
435
436 return ModRefInfo::ModRef;
437}
438
440 const CallBase *Call2,
441 AAQueryInfo &AAQI) {
442 if (!EnableTBAA)
443 return ModRefInfo::ModRef;
444
445 if (const MDNode *M1 = Call1->getMetadata(LLVMContext::MD_tbaa))
446 if (const MDNode *M2 = Call2->getMetadata(LLVMContext::MD_tbaa))
447 if (!Aliases(M1, M2))
449
450 return ModRefInfo::ModRef;
451}
452
454 if (!isStructPathTBAA(this)) {
455 if (getNumOperands() < 1)
456 return false;
457 if (MDString *Tag1 = dyn_cast<MDString>(getOperand(0))) {
458 if (Tag1->getString() == "vtable pointer")
459 return true;
460 }
461 return false;
462 }
463
464 // For struct-path aware TBAA, we use the access type of the tag.
465 TBAAStructTagNode Tag(this);
466 TBAAStructTypeNode AccessType(Tag.getAccessType());
467 if(auto *Id = dyn_cast<MDString>(AccessType.getId()))
468 if (Id->getString() == "vtable pointer")
469 return true;
470 return false;
471}
472
473static bool matchAccessTags(const MDNode *A, const MDNode *B,
474 const MDNode **GenericTag = nullptr);
475
477 const MDNode *GenericTag;
478 matchAccessTags(A, B, &GenericTag);
479 return const_cast<MDNode*>(GenericTag);
480}
481
482static const MDNode *getLeastCommonType(const MDNode *A, const MDNode *B) {
483 if (!A || !B)
484 return nullptr;
485
486 if (A == B)
487 return A;
488
490 TBAANode TA(A);
491 while (TA.getNode()) {
492 if (!PathA.insert(TA.getNode()))
493 report_fatal_error("Cycle found in TBAA metadata.");
494 TA = TA.getParent();
495 }
496
498 TBAANode TB(B);
499 while (TB.getNode()) {
500 if (!PathB.insert(TB.getNode()))
501 report_fatal_error("Cycle found in TBAA metadata.");
502 TB = TB.getParent();
503 }
504
505 int IA = PathA.size() - 1;
506 int IB = PathB.size() - 1;
507
508 const MDNode *Ret = nullptr;
509 while (IA >= 0 && IB >= 0) {
510 if (PathA[IA] == PathB[IB])
511 Ret = PathA[IA];
512 else
513 break;
514 --IA;
515 --IB;
516 }
517
518 return Ret;
519}
520
522 AAMDNodes Result;
523 Result.TBAA = MDNode::getMostGenericTBAA(TBAA, Other.TBAA);
524 Result.TBAAStruct = nullptr;
525 Result.Scope = MDNode::getMostGenericAliasScope(Scope, Other.Scope);
526 Result.NoAlias = MDNode::intersect(NoAlias, Other.NoAlias);
527 return Result;
528}
529
531 AAMDNodes Result;
532 Result.TBAA = Result.TBAAStruct = nullptr;
533 Result.Scope = MDNode::getMostGenericAliasScope(Scope, Other.Scope);
534 Result.NoAlias = MDNode::intersect(NoAlias, Other.NoAlias);
535 return Result;
536}
537
538static const MDNode *createAccessTag(const MDNode *AccessType) {
539 // If there is no access type or the access type is the root node, then
540 // we don't have any useful access tag to return.
541 if (!AccessType || AccessType->getNumOperands() < 2)
542 return nullptr;
543
544 Type *Int64 = IntegerType::get(AccessType->getContext(), 64);
545 auto *OffsetNode = ConstantAsMetadata::get(ConstantInt::get(Int64, 0));
546
547 if (TBAAStructTypeNode(AccessType).isNewFormat()) {
548 // TODO: Take access ranges into account when matching access tags and
549 // fix this code to generate actual access sizes for generic tags.
550 uint64_t AccessSize = UINT64_MAX;
551 auto *SizeNode =
552 ConstantAsMetadata::get(ConstantInt::get(Int64, AccessSize));
553 Metadata *Ops[] = {const_cast<MDNode*>(AccessType),
554 const_cast<MDNode*>(AccessType),
555 OffsetNode, SizeNode};
556 return MDNode::get(AccessType->getContext(), Ops);
557 }
558
559 Metadata *Ops[] = {const_cast<MDNode*>(AccessType),
560 const_cast<MDNode*>(AccessType),
561 OffsetNode};
562 return MDNode::get(AccessType->getContext(), Ops);
563}
564
565static bool hasField(TBAAStructTypeNode BaseType,
566 TBAAStructTypeNode FieldType) {
567 for (unsigned I = 0, E = BaseType.getNumFields(); I != E; ++I) {
568 TBAAStructTypeNode T = BaseType.getFieldType(I);
569 if (T == FieldType || hasField(T, FieldType))
570 return true;
571 }
572 return false;
573}
574
575/// Return true if for two given accesses, one of the accessed objects may be a
576/// subobject of the other. The \p BaseTag and \p SubobjectTag parameters
577/// describe the accesses to the base object and the subobject respectively.
578/// \p CommonType must be the metadata node describing the common type of the
579/// accessed objects. On return, \p MayAlias is set to true iff these accesses
580/// may alias and \p Generic, if not null, points to the most generic access
581/// tag for the given two.
582static bool mayBeAccessToSubobjectOf(TBAAStructTagNode BaseTag,
583 TBAAStructTagNode SubobjectTag,
584 const MDNode *CommonType,
585 const MDNode **GenericTag,
586 bool &MayAlias) {
587 // If the base object is of the least common type, then this may be an access
588 // to its subobject.
589 if (BaseTag.getAccessType() == BaseTag.getBaseType() &&
590 BaseTag.getAccessType() == CommonType) {
591 if (GenericTag)
592 *GenericTag = createAccessTag(CommonType);
593 MayAlias = true;
594 return true;
595 }
596
597 // If the access to the base object is through a field of the subobject's
598 // type, then this may be an access to that field. To check for that we start
599 // from the base type, follow the edge with the correct offset in the type DAG
600 // and adjust the offset until we reach the field type or until we reach the
601 // access type.
602 bool NewFormat = BaseTag.isNewFormat();
603 TBAAStructTypeNode BaseType(BaseTag.getBaseType());
604 uint64_t OffsetInBase = BaseTag.getOffset();
605
606 for (;;) {
607 // In the old format there is no distinction between fields and parent
608 // types, so in this case we consider all nodes up to the root.
609 if (!BaseType.getNode()) {
610 assert(!NewFormat && "Did not see access type in access path!");
611 break;
612 }
613
614 if (BaseType.getNode() == SubobjectTag.getBaseType()) {
615 bool SameMemberAccess = OffsetInBase == SubobjectTag.getOffset();
616 if (GenericTag) {
617 *GenericTag = SameMemberAccess ? SubobjectTag.getNode() :
618 createAccessTag(CommonType);
619 }
620 MayAlias = SameMemberAccess;
621 return true;
622 }
623
624 // With new-format nodes we stop at the access type.
625 if (NewFormat && BaseType.getNode() == BaseTag.getAccessType())
626 break;
627
628 // Follow the edge with the correct offset. Offset will be adjusted to
629 // be relative to the field type.
630 BaseType = BaseType.getField(OffsetInBase);
631 }
632
633 // If the base object has a direct or indirect field of the subobject's type,
634 // then this may be an access to that field. We need this to check now that
635 // we support aggregates as access types.
636 if (NewFormat) {
637 // TBAAStructTypeNode BaseAccessType(BaseTag.getAccessType());
638 TBAAStructTypeNode FieldType(SubobjectTag.getBaseType());
639 if (hasField(BaseType, FieldType)) {
640 if (GenericTag)
641 *GenericTag = createAccessTag(CommonType);
642 MayAlias = true;
643 return true;
644 }
645 }
646
647 return false;
648}
649
650/// matchTags - Return true if the given couple of accesses are allowed to
651/// overlap. If \arg GenericTag is not null, then on return it points to the
652/// most generic access descriptor for the given two.
653static bool matchAccessTags(const MDNode *A, const MDNode *B,
654 const MDNode **GenericTag) {
655 if (A == B) {
656 if (GenericTag)
657 *GenericTag = A;
658 return true;
659 }
660
661 // Accesses with no TBAA information may alias with any other accesses.
662 if (!A || !B) {
663 if (GenericTag)
664 *GenericTag = nullptr;
665 return true;
666 }
667
668 // Verify that both input nodes are struct-path aware. Auto-upgrade should
669 // have taken care of this.
670 assert(isStructPathTBAA(A) && "Access A is not struct-path aware!");
671 assert(isStructPathTBAA(B) && "Access B is not struct-path aware!");
672
673 TBAAStructTagNode TagA(A), TagB(B);
674 const MDNode *CommonType = getLeastCommonType(TagA.getAccessType(),
675 TagB.getAccessType());
676
677 // If the final access types have different roots, they're part of different
678 // potentially unrelated type systems, so we must be conservative.
679 if (!CommonType) {
680 if (GenericTag)
681 *GenericTag = nullptr;
682 return true;
683 }
684
685 // If one of the accessed objects may be a subobject of the other, then such
686 // accesses may alias.
687 bool MayAlias;
688 if (mayBeAccessToSubobjectOf(/* BaseTag= */ TagA, /* SubobjectTag= */ TagB,
689 CommonType, GenericTag, MayAlias) ||
690 mayBeAccessToSubobjectOf(/* BaseTag= */ TagB, /* SubobjectTag= */ TagA,
691 CommonType, GenericTag, MayAlias))
692 return MayAlias;
693
694 // Otherwise, we've proved there's no alias.
695 if (GenericTag)
696 *GenericTag = createAccessTag(CommonType);
697 return false;
698}
699
700/// Aliases - Test whether the access represented by tag A may alias the
701/// access represented by tag B.
702bool TypeBasedAAResult::Aliases(const MDNode *A, const MDNode *B) const {
703 return matchAccessTags(A, B);
704}
705
706AnalysisKey TypeBasedAA::Key;
707
709 return TypeBasedAAResult();
710}
711
713INITIALIZE_PASS(TypeBasedAAWrapperPass, "tbaa", "Type-Based Alias Analysis",
714 false, true)
715
717 return new TypeBasedAAWrapperPass();
718}
719
722}
723
725 Result.reset(new TypeBasedAAResult());
726 return false;
727}
728
730 Result.reset();
731 return false;
732}
733
735 AU.setPreservesAll();
736}
737
739 // Fast path if there's no offset
740 if (Offset == 0)
741 return MD;
742 // Fast path if there's no path tbaa node (and thus scalar)
743 if (!isStructPathTBAA(MD))
744 return MD;
745
746 // The correct behavior here is to add the offset into the TBAA
747 // struct node offset. The base type, however may not have defined
748 // a type at this additional offset, resulting in errors. Since
749 // this method is only used within a given load/store access
750 // the offset provided is only used to subdivide the previous load
751 // maintaining the validity of the previous TBAA.
752 //
753 // This, however, should be revisited in the future.
754 return MD;
755}
756
758 // Fast path if there's no offset
759 if (Offset == 0)
760 return MD;
762 for (size_t i = 0, size = MD->getNumOperands(); i < size; i += 3) {
763 ConstantInt *InnerOffset = mdconst::extract<ConstantInt>(MD->getOperand(i));
764 ConstantInt *InnerSize =
765 mdconst::extract<ConstantInt>(MD->getOperand(i + 1));
766 // Don't include any triples that aren't in bounds
767 if (InnerOffset->getZExtValue() + InnerSize->getZExtValue() <= Offset)
768 continue;
769
770 uint64_t NewSize = InnerSize->getZExtValue();
771 uint64_t NewOffset = InnerOffset->getZExtValue() - Offset;
772 if (InnerOffset->getZExtValue() < Offset) {
773 NewOffset = 0;
774 NewSize -= Offset - InnerOffset->getZExtValue();
775 }
776
777 // Shift the offset of the triple
779 ConstantInt::get(InnerOffset->getType(), NewOffset)));
781 ConstantInt::get(InnerSize->getType(), NewSize)));
782 Sub.push_back(MD->getOperand(i + 2));
783 }
784 return MDNode::get(MD->getContext(), Sub);
785}
786
788 // Fast path if 0-length
789 if (Len == 0)
790 return nullptr;
791
792 // Regular TBAA is invariant of length, so we only need to consider
793 // struct-path TBAA.
794 if (!isStructPathTBAA(MD))
795 return MD;
796
797 TBAAStructTagNode Tag(MD);
798
799 // Only new format TBAA has a size
800 if (!Tag.isNewFormat())
801 return MD;
802
803 // If unknown size, drop the TBAA.
804 if (Len == -1)
805 return nullptr;
806
807 // Otherwise, create TBAA with the new Len
808 ArrayRef<MDOperand> MDOperands = MD->operands();
809 SmallVector<Metadata *, 4> NextNodes(MDOperands.begin(), MDOperands.end());
810 ConstantInt *PreviousSize = mdconst::extract<ConstantInt>(NextNodes[3]);
811
812 // Don't create a new MDNode if it is the same length.
813 if (PreviousSize->equalsInt(Len))
814 return MD;
815
816 NextNodes[3] =
817 ConstantAsMetadata::get(ConstantInt::get(PreviousSize->getType(), Len));
818 return MDNode::get(MD->getContext(), NextNodes);
819}
820
822 AAMDNodes New = *this;
823 MDNode *M = New.TBAAStruct;
824 if (M && M->getNumOperands() >= 3 && M->getOperand(0) &&
825 mdconst::hasa<ConstantInt>(M->getOperand(0)) &&
826 mdconst::extract<ConstantInt>(M->getOperand(0))->isZero() &&
827 M->getOperand(1) && mdconst::hasa<ConstantInt>(M->getOperand(1)) &&
828 mdconst::extract<ConstantInt>(M->getOperand(1))->getValue() ==
829 AccessSize &&
830 M->getOperand(2) && isa<MDNode>(M->getOperand(2))) {
831 New.TBAAStruct = nullptr;
832 New.TBAA = cast<MDNode>(M->getOperand(2));
833 }
834 return New;
835}
836
838 const DataLayout &DL) {
839 AAMDNodes New = shift(Offset);
840 if (!DL.typeSizeEqualsStoreSize(AccessTy))
841 return New;
842 TypeSize Size = DL.getTypeStoreSize(AccessTy);
843 if (Size.isScalable())
844 return New;
845
846 return New.adjustForAccess(Size.getKnownMinValue());
847}
848
849AAMDNodes AAMDNodes::adjustForAccess(size_t Offset, unsigned AccessSize) {
850 AAMDNodes New = shift(Offset);
851 return New.adjustForAccess(AccessSize);
852}
MachineBasicBlock MachineBasicBlock::iterator DebugLoc DL
static msgpack::DocNode getNode(msgpack::DocNode DN, msgpack::Type Type, MCValue Val)
static const Function * getParent(const Value *V)
static GCRegistry::Add< OcamlGC > B("ocaml", "ocaml 3.10-compatible GC")
static GCRegistry::Add< ErlangGC > A("erlang", "erlang-compatible garbage collector")
This file contains the declarations for the subclasses of Constant, which represent the different fla...
Returns the sub type a function will return at a given Idx Should correspond to the result type of an ExtractValue instruction executed with just that one unsigned Idx
uint64_t Size
std::optional< std::vector< StOtherPiece > > Other
Definition: ELFYAML.cpp:1293
static MemAccessTy getAccessType(const TargetTransformInfo &TTI, Instruction *Inst, Value *OperandVal)
Return the type of the memory being accessed.
#define F(x, y, z)
Definition: MD5.cpp:55
#define I(x, y, z)
Definition: MD5.cpp:58
mir Rename Register Operands
This file provides utility analysis objects describing memory locations.
This file contains the declarations for metadata subclasses.
#define P(N)
#define INITIALIZE_PASS(passName, arg, name, cfg, analysis)
Definition: PassSupport.h:38
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
unsigned OpIndex
static enum BaseType getBaseType(const Value *Val)
Return the baseType for Val which states whether Val is exclusively derived from constant/null,...
This file implements a set that has insertion order iteration characteristics.
static bool matchAccessTags(const MDNode *A, const MDNode *B, const MDNode **GenericTag=nullptr)
matchTags - Return true if the given couple of accesses are allowed to overlap.
static cl::opt< bool > EnableTBAA("enable-tbaa", cl::init(true), cl::Hidden)
static bool isStructPathTBAA(const MDNode *MD)
Check the first operand of the tbaa tag node, if it is a MDNode, we treat it as struct-path aware TBA...
static bool mayBeAccessToSubobjectOf(TBAAStructTagNode BaseTag, TBAAStructTagNode SubobjectTag, const MDNode *CommonType, const MDNode **GenericTag, bool &MayAlias)
Return true if for two given accesses, one of the accessed objects may be a subobject of the other.
static bool hasField(TBAAStructTypeNode BaseType, TBAAStructTypeNode FieldType)
static const MDNode * createAccessTag(const MDNode *AccessType)
static const MDNode * getLeastCommonType(const MDNode *A, const MDNode *B)
This is the interface for a metadata-based TBAA.
static unsigned getSize(unsigned Kind)
This class stores info we want to provide to or retain within an alias query.
The possible results of an alias query.
Definition: AliasAnalysis.h:81
@ MayAlias
The two locations may or may not alias.
@ NoAlias
The two locations do not alias at all.
Definition: AliasAnalysis.h:99
A container for analyses that lazily runs them and caches their results.
Definition: PassManager.h:321
Represent the analysis usage information of a pass.
void setPreservesAll()
Set by analyses that do not transform their input at all.
ArrayRef - Represent a constant reference to an array (0 or more elements consecutively in memory),...
Definition: ArrayRef.h:41
iterator end() const
Definition: ArrayRef.h:154
iterator begin() const
Definition: ArrayRef.h:153
Base class for all callable instructions (InvokeInst and CallInst) Holds everything related to callin...
Definition: InstrTypes.h:1494
static ConstantAsMetadata * get(Constant *C)
Definition: Metadata.h:528
This is the shared class of boolean and integer constants.
Definition: Constants.h:81
uint64_t getZExtValue() const
Return the constant as a 64-bit unsigned integer value after it has been zero extended as appropriate...
Definition: Constants.h:155
bool equalsInt(uint64_t V) const
A helper method that can be used to determine if the constant contained within is equal to a constant...
Definition: Constants.h:181
const APInt & getValue() const
Return the constant as an APInt value reference.
Definition: Constants.h:146
A parsed version of the target data layout string in and methods for querying it.
Definition: DataLayout.h:110
ImmutablePass class - This class is used to provide information that does not need to be run.
Definition: Pass.h:282
MDNode * getMetadata(unsigned KindID) const
Get the metadata of given kind attached to this Instruction.
Definition: Instruction.h:359
static IntegerType * get(LLVMContext &C, unsigned NumBits)
This static method is the primary way of constructing an IntegerType.
Definition: Type.cpp:278
Metadata node.
Definition: Metadata.h:1067
static MDNode * getMostGenericAliasScope(MDNode *A, MDNode *B)
Definition: Metadata.cpp:1135
bool isTBAAVtableAccess() const
Check whether MDNode is a vtable access.
static MDNode * getMostGenericTBAA(MDNode *A, MDNode *B)
const MDOperand & getOperand(unsigned I) const
Definition: Metadata.h:1428
ArrayRef< MDOperand > operands() const
Definition: Metadata.h:1426
static MDTuple * get(LLVMContext &Context, ArrayRef< Metadata * > MDs)
Definition: Metadata.h:1541
unsigned getNumOperands() const
Return number of MDNode operands.
Definition: Metadata.h:1434
static MDNode * intersect(MDNode *A, MDNode *B)
Definition: Metadata.cpp:1122
LLVMContext & getContext() const
Definition: Metadata.h:1231
A single uniqued string.
Definition: Metadata.h:720
static MemoryEffectsBase none()
Create MemoryEffectsBase that cannot read or write any memory.
Definition: ModRef.h:117
static MemoryEffectsBase unknown()
Create MemoryEffectsBase that can read and write any memory.
Definition: ModRef.h:112
Representation for a specific memory location.
AAMDNodes AATags
The metadata nodes which describes the aliasing of the location (each member is null if that kind of ...
Root of the metadata hierarchy.
Definition: Metadata.h:62
A Module instance is used to store all the information related to an LLVM module.
Definition: Module.h:65
static PassRegistry * getPassRegistry()
getPassRegistry - Access the global registry object, which is automatically initialized at applicatio...
size_type size() const
Determine the number of elements in the SetVector.
Definition: SetVector.h:98
bool insert(const value_type &X)
Insert a new element into the SetVector.
Definition: SetVector.h:162
A SetVector that performs no allocations if smaller than a certain size.
Definition: SetVector.h:370
void push_back(const T &Elt)
Definition: SmallVector.h:426
This is a 'vector' (really, a variable-sized array), optimized for the case when the array is small.
Definition: SmallVector.h:1209
A simple AA result that uses TBAA metadata to answer queries.
AliasResult alias(const MemoryLocation &LocA, const MemoryLocation &LocB, AAQueryInfo &AAQI, const Instruction *CtxI)
ModRefInfo getModRefInfoMask(const MemoryLocation &Loc, AAQueryInfo &AAQI, bool IgnoreLocals)
ModRefInfo getModRefInfo(const CallBase *Call, const MemoryLocation &Loc, AAQueryInfo &AAQI)
MemoryEffects getMemoryEffects(const CallBase *Call, AAQueryInfo &AAQI)
Legacy wrapper pass to provide the TypeBasedAAResult object.
bool doFinalization(Module &M) override
doFinalization - Virtual method overriden by subclasses to do any necessary clean up after all passes...
bool doInitialization(Module &M) override
doInitialization - Virtual method overridden by subclasses to do any necessary initialization before ...
void getAnalysisUsage(AnalysisUsage &AU) const override
getAnalysisUsage - This function should be overriden by passes that need analysis information to do t...
TypeBasedAAResult run(Function &F, FunctionAnalysisManager &AM)
The instances of the Type class are immutable: once they are created, they are never changed.
Definition: Type.h:45
Type * getType() const
All values are typed, get the type of this value.
Definition: Value.h:255
#define UINT64_MAX
Definition: DataTypes.h:77
initializer< Ty > init(const Ty &Val)
Definition: CommandLine.h:450
This is an optimization pass for GlobalISel generic memory operations.
Definition: AddressRanges.h:18
@ Offset
Definition: DWP.cpp:456
void initializeTypeBasedAAWrapperPassPass(PassRegistry &)
auto size(R &&Range, std::enable_if_t< std::is_base_of< std::random_access_iterator_tag, typename std::iterator_traits< decltype(Range.begin())>::iterator_category >::value, void > *=nullptr)
Get the size of a range.
Definition: STLExtras.h:1680
bool operator==(const AddressRangeValuePair &LHS, const AddressRangeValuePair &RHS)
unsigned M1(unsigned Val)
Definition: VE.h:376
static Error getOffset(const SymbolRef &Sym, SectionRef Sec, uint64_t &Result)
void report_fatal_error(Error Err, bool gen_crash_diag=true)
Report a serious error, calling any installed error handler.
Definition: Error.cpp:167
ModRefInfo
Flags indicating whether a memory access modifies or references memory.
Definition: ModRef.h:27
@ ModRef
The access may reference and may modify the value stored in memory.
@ NoModRef
The access neither references nor modifies the value stored in memory.
@ Other
Any other memory.
ImmutablePass * createTypeBasedAAWrapperPass()
#define N
A collection of metadata nodes that might be associated with a memory access used by the alias-analys...
Definition: Metadata.h:760
AAMDNodes concat(const AAMDNodes &Other) const
Determine the best AAMDNodes after concatenating two different locations together.
static MDNode * shiftTBAAStruct(MDNode *M, size_t off)
MDNode * Scope
The tag for alias scope specification (used with noalias).
Definition: Metadata.h:783
static MDNode * extendToTBAA(MDNode *TBAA, ssize_t len)
MDNode * TBAA
The tag for type-based alias analysis.
Definition: Metadata.h:777
AAMDNodes shift(size_t Offset) const
Create a new AAMDNode that describes this AAMDNode after applying a constant offset to the start of t...
Definition: Metadata.h:814
AAMDNodes merge(const AAMDNodes &Other) const
Given two sets of AAMDNodes applying to potentially different locations, determine the best AAMDNodes...
MDNode * NoAlias
The tag specifying the noalias scope.
Definition: Metadata.h:786
AAMDNodes adjustForAccess(unsigned AccessSize)
Create a new AAMDNode for accessing AccessSize bytes of this AAMDNode.
static MDNode * shiftTBAA(MDNode *M, size_t off)
A special type used by analysis passes to provide an address that identifies that particular analysis...
Definition: Analysis.h:26