LLVM 17.0.0git
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)
378 return AAResultBase::alias(LocA, LocB, AAQI, nullptr);
379
380 // If accesses may alias, chain to the next AliasAnalysis.
381 if (Aliases(LocA.AATags.TBAA, LocB.AATags.TBAA))
382 return AAResultBase::alias(LocA, LocB, AAQI, nullptr);
383
384 // Otherwise return a definitive result.
386}
387
389 AAQueryInfo &AAQI,
390 bool IgnoreLocals) {
391 if (!EnableTBAA)
392 return AAResultBase::getModRefInfoMask(Loc, AAQI, IgnoreLocals);
393
394 const MDNode *M = Loc.AATags.TBAA;
395 if (!M)
396 return AAResultBase::getModRefInfoMask(Loc, AAQI, IgnoreLocals);
397
398 // If this is an "immutable" type, we can assume the pointer is pointing
399 // to constant memory.
400 if ((!isStructPathTBAA(M) && TBAANode(M).isTypeImmutable()) ||
401 (isStructPathTBAA(M) && TBAAStructTagNode(M).isTypeImmutable()))
403
404 return AAResultBase::getModRefInfoMask(Loc, AAQI, IgnoreLocals);
405}
406
408 AAQueryInfo &AAQI) {
409 if (!EnableTBAA)
410 return AAResultBase::getMemoryEffects(Call, AAQI);
411
412 // If this is an "immutable" type, the access is not observable.
413 if (const MDNode *M = Call->getMetadata(LLVMContext::MD_tbaa))
414 if ((!isStructPathTBAA(M) && TBAANode(M).isTypeImmutable()) ||
415 (isStructPathTBAA(M) && TBAAStructTagNode(M).isTypeImmutable()))
416 return MemoryEffects::none();
417
418 return AAResultBase::getMemoryEffects(Call, AAQI);
419}
420
422 // Functions don't have metadata. Just chain to the next implementation.
424}
425
427 const MemoryLocation &Loc,
428 AAQueryInfo &AAQI) {
429 if (!EnableTBAA)
430 return AAResultBase::getModRefInfo(Call, Loc, AAQI);
431
432 if (const MDNode *L = Loc.AATags.TBAA)
433 if (const MDNode *M = Call->getMetadata(LLVMContext::MD_tbaa))
434 if (!Aliases(L, M))
436
437 return AAResultBase::getModRefInfo(Call, Loc, AAQI);
438}
439
441 const CallBase *Call2,
442 AAQueryInfo &AAQI) {
443 if (!EnableTBAA)
444 return AAResultBase::getModRefInfo(Call1, Call2, AAQI);
445
446 if (const MDNode *M1 = Call1->getMetadata(LLVMContext::MD_tbaa))
447 if (const MDNode *M2 = Call2->getMetadata(LLVMContext::MD_tbaa))
448 if (!Aliases(M1, M2))
450
451 return AAResultBase::getModRefInfo(Call1, Call2, AAQI);
452}
453
455 if (!isStructPathTBAA(this)) {
456 if (getNumOperands() < 1)
457 return false;
458 if (MDString *Tag1 = dyn_cast<MDString>(getOperand(0))) {
459 if (Tag1->getString() == "vtable pointer")
460 return true;
461 }
462 return false;
463 }
464
465 // For struct-path aware TBAA, we use the access type of the tag.
466 TBAAStructTagNode Tag(this);
467 TBAAStructTypeNode AccessType(Tag.getAccessType());
468 if(auto *Id = dyn_cast<MDString>(AccessType.getId()))
469 if (Id->getString() == "vtable pointer")
470 return true;
471 return false;
472}
473
474static bool matchAccessTags(const MDNode *A, const MDNode *B,
475 const MDNode **GenericTag = nullptr);
476
478 const MDNode *GenericTag;
479 matchAccessTags(A, B, &GenericTag);
480 return const_cast<MDNode*>(GenericTag);
481}
482
483static const MDNode *getLeastCommonType(const MDNode *A, const MDNode *B) {
484 if (!A || !B)
485 return nullptr;
486
487 if (A == B)
488 return A;
489
491 TBAANode TA(A);
492 while (TA.getNode()) {
493 if (!PathA.insert(TA.getNode()))
494 report_fatal_error("Cycle found in TBAA metadata.");
495 TA = TA.getParent();
496 }
497
499 TBAANode TB(B);
500 while (TB.getNode()) {
501 if (!PathB.insert(TB.getNode()))
502 report_fatal_error("Cycle found in TBAA metadata.");
503 TB = TB.getParent();
504 }
505
506 int IA = PathA.size() - 1;
507 int IB = PathB.size() - 1;
508
509 const MDNode *Ret = nullptr;
510 while (IA >= 0 && IB >= 0) {
511 if (PathA[IA] == PathB[IB])
512 Ret = PathA[IA];
513 else
514 break;
515 --IA;
516 --IB;
517 }
518
519 return Ret;
520}
521
523 AAMDNodes Result;
524 Result.TBAA = MDNode::getMostGenericTBAA(TBAA, Other.TBAA);
525 Result.TBAAStruct = nullptr;
526 Result.Scope = MDNode::getMostGenericAliasScope(Scope, Other.Scope);
527 Result.NoAlias = MDNode::intersect(NoAlias, Other.NoAlias);
528 return Result;
529}
530
532 AAMDNodes Result;
533 Result.TBAA = Result.TBAAStruct = nullptr;
534 Result.Scope = MDNode::getMostGenericAliasScope(Scope, Other.Scope);
535 Result.NoAlias = MDNode::intersect(NoAlias, Other.NoAlias);
536 return Result;
537}
538
539static const MDNode *createAccessTag(const MDNode *AccessType) {
540 // If there is no access type or the access type is the root node, then
541 // we don't have any useful access tag to return.
542 if (!AccessType || AccessType->getNumOperands() < 2)
543 return nullptr;
544
545 Type *Int64 = IntegerType::get(AccessType->getContext(), 64);
546 auto *OffsetNode = ConstantAsMetadata::get(ConstantInt::get(Int64, 0));
547
548 if (TBAAStructTypeNode(AccessType).isNewFormat()) {
549 // TODO: Take access ranges into account when matching access tags and
550 // fix this code to generate actual access sizes for generic tags.
551 uint64_t AccessSize = UINT64_MAX;
552 auto *SizeNode =
554 Metadata *Ops[] = {const_cast<MDNode*>(AccessType),
555 const_cast<MDNode*>(AccessType),
556 OffsetNode, SizeNode};
557 return MDNode::get(AccessType->getContext(), Ops);
558 }
559
560 Metadata *Ops[] = {const_cast<MDNode*>(AccessType),
561 const_cast<MDNode*>(AccessType),
562 OffsetNode};
563 return MDNode::get(AccessType->getContext(), Ops);
564}
565
566static bool hasField(TBAAStructTypeNode BaseType,
567 TBAAStructTypeNode FieldType) {
568 for (unsigned I = 0, E = BaseType.getNumFields(); I != E; ++I) {
569 TBAAStructTypeNode T = BaseType.getFieldType(I);
570 if (T == FieldType || hasField(T, FieldType))
571 return true;
572 }
573 return false;
574}
575
576/// Return true if for two given accesses, one of the accessed objects may be a
577/// subobject of the other. The \p BaseTag and \p SubobjectTag parameters
578/// describe the accesses to the base object and the subobject respectively.
579/// \p CommonType must be the metadata node describing the common type of the
580/// accessed objects. On return, \p MayAlias is set to true iff these accesses
581/// may alias and \p Generic, if not null, points to the most generic access
582/// tag for the given two.
583static bool mayBeAccessToSubobjectOf(TBAAStructTagNode BaseTag,
584 TBAAStructTagNode SubobjectTag,
585 const MDNode *CommonType,
586 const MDNode **GenericTag,
587 bool &MayAlias) {
588 // If the base object is of the least common type, then this may be an access
589 // to its subobject.
590 if (BaseTag.getAccessType() == BaseTag.getBaseType() &&
591 BaseTag.getAccessType() == CommonType) {
592 if (GenericTag)
593 *GenericTag = createAccessTag(CommonType);
594 MayAlias = true;
595 return true;
596 }
597
598 // If the access to the base object is through a field of the subobject's
599 // type, then this may be an access to that field. To check for that we start
600 // from the base type, follow the edge with the correct offset in the type DAG
601 // and adjust the offset until we reach the field type or until we reach the
602 // access type.
603 bool NewFormat = BaseTag.isNewFormat();
604 TBAAStructTypeNode BaseType(BaseTag.getBaseType());
605 uint64_t OffsetInBase = BaseTag.getOffset();
606
607 for (;;) {
608 // In the old format there is no distinction between fields and parent
609 // types, so in this case we consider all nodes up to the root.
610 if (!BaseType.getNode()) {
611 assert(!NewFormat && "Did not see access type in access path!");
612 break;
613 }
614
615 if (BaseType.getNode() == SubobjectTag.getBaseType()) {
616 bool SameMemberAccess = OffsetInBase == SubobjectTag.getOffset();
617 if (GenericTag) {
618 *GenericTag = SameMemberAccess ? SubobjectTag.getNode() :
619 createAccessTag(CommonType);
620 }
621 MayAlias = SameMemberAccess;
622 return true;
623 }
624
625 // With new-format nodes we stop at the access type.
626 if (NewFormat && BaseType.getNode() == BaseTag.getAccessType())
627 break;
628
629 // Follow the edge with the correct offset. Offset will be adjusted to
630 // be relative to the field type.
631 BaseType = BaseType.getField(OffsetInBase);
632 }
633
634 // If the base object has a direct or indirect field of the subobject's type,
635 // then this may be an access to that field. We need this to check now that
636 // we support aggregates as access types.
637 if (NewFormat) {
638 // TBAAStructTypeNode BaseAccessType(BaseTag.getAccessType());
639 TBAAStructTypeNode FieldType(SubobjectTag.getBaseType());
640 if (hasField(BaseType, FieldType)) {
641 if (GenericTag)
642 *GenericTag = createAccessTag(CommonType);
643 MayAlias = true;
644 return true;
645 }
646 }
647
648 return false;
649}
650
651/// matchTags - Return true if the given couple of accesses are allowed to
652/// overlap. If \arg GenericTag is not null, then on return it points to the
653/// most generic access descriptor for the given two.
654static bool matchAccessTags(const MDNode *A, const MDNode *B,
655 const MDNode **GenericTag) {
656 if (A == B) {
657 if (GenericTag)
658 *GenericTag = A;
659 return true;
660 }
661
662 // Accesses with no TBAA information may alias with any other accesses.
663 if (!A || !B) {
664 if (GenericTag)
665 *GenericTag = nullptr;
666 return true;
667 }
668
669 // Verify that both input nodes are struct-path aware. Auto-upgrade should
670 // have taken care of this.
671 assert(isStructPathTBAA(A) && "Access A is not struct-path aware!");
672 assert(isStructPathTBAA(B) && "Access B is not struct-path aware!");
673
674 TBAAStructTagNode TagA(A), TagB(B);
675 const MDNode *CommonType = getLeastCommonType(TagA.getAccessType(),
676 TagB.getAccessType());
677
678 // If the final access types have different roots, they're part of different
679 // potentially unrelated type systems, so we must be conservative.
680 if (!CommonType) {
681 if (GenericTag)
682 *GenericTag = nullptr;
683 return true;
684 }
685
686 // If one of the accessed objects may be a subobject of the other, then such
687 // accesses may alias.
688 bool MayAlias;
689 if (mayBeAccessToSubobjectOf(/* BaseTag= */ TagA, /* SubobjectTag= */ TagB,
690 CommonType, GenericTag, MayAlias) ||
691 mayBeAccessToSubobjectOf(/* BaseTag= */ TagB, /* SubobjectTag= */ TagA,
692 CommonType, GenericTag, MayAlias))
693 return MayAlias;
694
695 // Otherwise, we've proved there's no alias.
696 if (GenericTag)
697 *GenericTag = createAccessTag(CommonType);
698 return false;
699}
700
701/// Aliases - Test whether the access represented by tag A may alias the
702/// access represented by tag B.
703bool TypeBasedAAResult::Aliases(const MDNode *A, const MDNode *B) const {
704 return matchAccessTags(A, B);
705}
706
707AnalysisKey TypeBasedAA::Key;
708
710 return TypeBasedAAResult();
711}
712
714INITIALIZE_PASS(TypeBasedAAWrapperPass, "tbaa", "Type-Based Alias Analysis",
715 false, true)
716
718 return new TypeBasedAAWrapperPass();
719}
720
723}
724
726 Result.reset(new TypeBasedAAResult());
727 return false;
728}
729
731 Result.reset();
732 return false;
733}
734
736 AU.setPreservesAll();
737}
738
740 // Fast path if there's no offset
741 if (Offset == 0)
742 return MD;
743 // Fast path if there's no path tbaa node (and thus scalar)
744 if (!isStructPathTBAA(MD))
745 return MD;
746
747 // The correct behavior here is to add the offset into the TBAA
748 // struct node offset. The base type, however may not have defined
749 // a type at this additional offset, resulting in errors. Since
750 // this method is only used within a given load/store access
751 // the offset provided is only used to subdivide the previous load
752 // maintaining the validity of the previous TBAA.
753 //
754 // This, however, should be revisited in the future.
755 return MD;
756}
757
759 // Fast path if there's no offset
760 if (Offset == 0)
761 return MD;
763 for (size_t i = 0, size = MD->getNumOperands(); i < size; i += 3) {
764 ConstantInt *InnerOffset = mdconst::extract<ConstantInt>(MD->getOperand(i));
765 ConstantInt *InnerSize =
766 mdconst::extract<ConstantInt>(MD->getOperand(i + 1));
767 // Don't include any triples that aren't in bounds
768 if (InnerOffset->getZExtValue() + InnerSize->getZExtValue() <= Offset)
769 continue;
770
771 uint64_t NewSize = InnerSize->getZExtValue();
772 uint64_t NewOffset = InnerOffset->getZExtValue() - Offset;
773 if (InnerOffset->getZExtValue() < Offset) {
774 NewOffset = 0;
775 NewSize -= Offset - InnerOffset->getZExtValue();
776 }
777
778 // Shift the offset of the triple
780 ConstantInt::get(InnerOffset->getType(), NewOffset)));
782 ConstantInt::get(InnerSize->getType(), NewSize)));
783 Sub.push_back(MD->getOperand(i + 2));
784 }
785 return MDNode::get(MD->getContext(), Sub);
786}
787
789 // Fast path if 0-length
790 if (Len == 0)
791 return nullptr;
792
793 // Regular TBAA is invariant of length, so we only need to consider
794 // struct-path TBAA.
795 if (!isStructPathTBAA(MD))
796 return MD;
797
798 TBAAStructTagNode Tag(MD);
799
800 // Only new format TBAA has a size
801 if (!Tag.isNewFormat())
802 return MD;
803
804 // If unknown size, drop the TBAA.
805 if (Len == -1)
806 return nullptr;
807
808 // Otherwise, create TBAA with the new Len
809 ArrayRef<MDOperand> MDOperands = MD->operands();
810 SmallVector<Metadata *, 4> NextNodes(MDOperands.begin(), MDOperands.end());
811 ConstantInt *PreviousSize = mdconst::extract<ConstantInt>(NextNodes[3]);
812
813 // Don't create a new MDNode if it is the same length.
814 if (PreviousSize->equalsInt(Len))
815 return MD;
816
817 NextNodes[3] =
818 ConstantAsMetadata::get(ConstantInt::get(PreviousSize->getType(), Len));
819 return MDNode::get(MD->getContext(), NextNodes);
820}
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")
static GCRegistry::Add< CoreCLRGC > E("coreclr", "CoreCLR-compatible GC")
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
std::optional< std::vector< StOtherPiece > > Other
Definition: ELFYAML.cpp:1260
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.
MemoryEffects getMemoryEffects(const CallBase *Call, AAQueryInfo &AAQI)
ModRefInfo getModRefInfoMask(const MemoryLocation &Loc, AAQueryInfo &AAQI, bool IgnoreLocals)
ModRefInfo getModRefInfo(const CallBase *Call, const MemoryLocation &Loc, AAQueryInfo &AAQI)
AliasResult alias(const MemoryLocation &LocA, const MemoryLocation &LocB, AAQueryInfo &AAQI, const Instruction *I)
The possible results of an alias query.
Definition: AliasAnalysis.h:83
@ NoAlias
The two locations do not alias at all.
A container for analyses that lazily runs them and caches their results.
Definition: PassManager.h:620
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:152
iterator begin() const
Definition: ArrayRef.h:151
Base class for all callable instructions (InvokeInst and CallInst) Holds everything related to callin...
Definition: InstrTypes.h:1186
static ConstantAsMetadata * get(Constant *C)
Definition: Metadata.h:419
This is the shared class of boolean and integer constants.
Definition: Constants.h:78
IntegerType * getType() const
getType - Specialize the getType() method to always return an IntegerType, which reduces the amount o...
Definition: Constants.h:176
static Constant * get(Type *Ty, uint64_t V, bool IsSigned=false)
If Ty is a vector type, return a Constant with a splat of the given value.
Definition: Constants.cpp:888
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:145
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:171
const APInt & getValue() const
Return the constant as an APInt value reference.
Definition: Constants.h:136
ImmutablePass class - This class is used to provide information that does not need to be run.
Definition: Pass.h:279
MDNode * getMetadata(unsigned KindID) const
Get the metadata of given kind attached to this Instruction.
Definition: Instruction.h:275
static IntegerType * get(LLVMContext &C, unsigned NumBits)
This static method is the primary way of constructing an IntegerType.
Definition: Type.cpp:331
Metadata node.
Definition: Metadata.h:943
static MDNode * getMostGenericAliasScope(MDNode *A, MDNode *B)
Definition: Metadata.cpp:1032
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:1291
ArrayRef< MDOperand > operands() const
Definition: Metadata.h:1289
static MDTuple * get(LLVMContext &Context, ArrayRef< Metadata * > MDs)
Definition: Metadata.h:1399
unsigned getNumOperands() const
Return number of MDNode operands.
Definition: Metadata.h:1297
static MDNode * intersect(MDNode *A, MDNode *B)
Definition: Metadata.cpp:1019
LLVMContext & getContext() const
Definition: Metadata.h:1107
A single uniqued string.
Definition: Metadata.h:611
Summary of how a function affects memory in the program.
Definition: ModRef.h:63
static MemoryEffects none()
Create MemoryEffects that cannot read or write any memory.
Definition: ModRef.h:118
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:61
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:77
bool insert(const value_type &X)
Insert a new element into the SetVector.
Definition: SetVector.h:141
A SetVector that performs no allocations if smaller than a certain size.
Definition: SetVector.h:301
void push_back(const T &Elt)
Definition: SmallVector.h:416
This is a 'vector' (really, a variable-sized array), optimized for the case when the array is small.
Definition: SmallVector.h:1200
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
#define UINT64_MAX
Definition: DataTypes.h:77
initializer< Ty > init(const Ty &Val)
Definition: CommandLine.h:445
This is an optimization pass for GlobalISel generic memory operations.
Definition: AddressRanges.h:18
@ Offset
Definition: DWP.cpp:406
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:1777
bool operator==(const AddressRangeValuePair &LHS, const AddressRangeValuePair &RHS)
unsigned M1(unsigned Val)
Definition: VE.h:468
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:145
ModRefInfo
Flags indicating whether a memory access modifies or references memory.
Definition: ModRef.h:27
@ NoModRef
The access neither references nor modifies the value stored in 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:651
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:674
static MDNode * extendToTBAA(MDNode *TBAA, ssize_t len)
MDNode * TBAA
The tag for type-based alias analysis.
Definition: Metadata.h:668
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:677
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: PassManager.h:69