1 //===- TypeBasedAliasAnalysis.cpp - Type-Based Alias Analysis -------------===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 // 10 // This file defines the TypeBasedAliasAnalysis pass, which implements 11 // metadata-based TBAA. 12 // 13 // In LLVM IR, memory does not have types, so LLVM's own type system is not 14 // suitable for doing TBAA. Instead, metadata is added to the IR to describe 15 // a type system of a higher level language. This can be used to implement 16 // typical C/C++ TBAA, but it can also be used to implement custom alias 17 // analysis behavior for other languages. 18 // 19 // We now support two types of metadata format: scalar TBAA and struct-path 20 // aware TBAA. After all testing cases are upgraded to use struct-path aware 21 // TBAA and we can auto-upgrade existing bc files, the support for scalar TBAA 22 // can be dropped. 23 // 24 // The scalar TBAA metadata format is very simple. TBAA MDNodes have up to 25 // three fields, e.g.: 26 // !0 = metadata !{ metadata !"an example type tree" } 27 // !1 = metadata !{ metadata !"int", metadata !0 } 28 // !2 = metadata !{ metadata !"float", metadata !0 } 29 // !3 = metadata !{ metadata !"const float", metadata !2, i64 1 } 30 // 31 // The first field is an identity field. It can be any value, usually 32 // an MDString, which uniquely identifies the type. The most important 33 // name in the tree is the name of the root node. Two trees with 34 // different root node names are entirely disjoint, even if they 35 // have leaves with common names. 36 // 37 // The second field identifies the type's parent node in the tree, or 38 // is null or omitted for a root node. A type is considered to alias 39 // all of its descendants and all of its ancestors in the tree. Also, 40 // a type is considered to alias all types in other trees, so that 41 // bitcode produced from multiple front-ends is handled conservatively. 42 // 43 // If the third field is present, it's an integer which if equal to 1 44 // indicates that the type is "constant" (meaning pointsToConstantMemory 45 // should return true; see 46 // http://llvm.org/docs/AliasAnalysis.html#OtherItfs). 47 // 48 // With struct-path aware TBAA, the MDNodes attached to an instruction using 49 // "!tbaa" are called path tag nodes. 50 // 51 // The path tag node has 4 fields with the last field being optional. 52 // 53 // The first field is the base type node, it can be a struct type node 54 // or a scalar type node. The second field is the access type node, it 55 // must be a scalar type node. The third field is the offset into the base type. 56 // The last field has the same meaning as the last field of our scalar TBAA: 57 // it's an integer which if equal to 1 indicates that the access is "constant". 58 // 59 // The struct type node has a name and a list of pairs, one pair for each member 60 // of the struct. The first element of each pair is a type node (a struct type 61 // node or a sclar type node), specifying the type of the member, the second 62 // element of each pair is the offset of the member. 63 // 64 // Given an example 65 // typedef struct { 66 // short s; 67 // } A; 68 // typedef struct { 69 // uint16_t s; 70 // A a; 71 // } B; 72 // 73 // For an acess to B.a.s, we attach !5 (a path tag node) to the load/store 74 // instruction. The base type is !4 (struct B), the access type is !2 (scalar 75 // type short) and the offset is 4. 76 // 77 // !0 = metadata !{metadata !"Simple C/C++ TBAA"} 78 // !1 = metadata !{metadata !"omnipotent char", metadata !0} // Scalar type node 79 // !2 = metadata !{metadata !"short", metadata !1} // Scalar type node 80 // !3 = metadata !{metadata !"A", metadata !2, i64 0} // Struct type node 81 // !4 = metadata !{metadata !"B", metadata !2, i64 0, metadata !3, i64 4} 82 // // Struct type node 83 // !5 = metadata !{metadata !4, metadata !2, i64 4} // Path tag node 84 // 85 // The struct type nodes and the scalar type nodes form a type DAG. 86 // Root (!0) 87 // char (!1) -- edge to Root 88 // short (!2) -- edge to char 89 // A (!3) -- edge with offset 0 to short 90 // B (!4) -- edge with offset 0 to short and edge with offset 4 to A 91 // 92 // To check if two tags (tagX and tagY) can alias, we start from the base type 93 // of tagX, follow the edge with the correct offset in the type DAG and adjust 94 // the offset until we reach the base type of tagY or until we reach the Root 95 // node. 96 // If we reach the base type of tagY, compare the adjusted offset with 97 // offset of tagY, return Alias if the offsets are the same, return NoAlias 98 // otherwise. 99 // If we reach the Root node, perform the above starting from base type of tagY 100 // to see if we reach base type of tagX. 101 // 102 // If they have different roots, they're part of different potentially 103 // unrelated type systems, so we return Alias to be conservative. 104 // If neither node is an ancestor of the other and they have the same root, 105 // then we say NoAlias. 106 // 107 // TODO: The current metadata format doesn't support struct 108 // fields. For example: 109 // struct X { 110 // double d; 111 // int i; 112 // }; 113 // void foo(struct X *x, struct X *y, double *p) { 114 // *x = *y; 115 // *p = 0.0; 116 // } 117 // Struct X has a double member, so the store to *x can alias the store to *p. 118 // Currently it's not possible to precisely describe all the things struct X 119 // aliases, so struct assignments must use conservative TBAA nodes. There's 120 // no scheme for attaching metadata to @llvm.memcpy yet either. 121 // 122 //===----------------------------------------------------------------------===// 123 124 #include "llvm/Analysis/TypeBasedAliasAnalysis.h" 125 #include "llvm/Analysis/TargetLibraryInfo.h" 126 #include "llvm/ADT/SetVector.h" 127 #include "llvm/IR/Constants.h" 128 #include "llvm/IR/LLVMContext.h" 129 #include "llvm/IR/Module.h" 130 #include "llvm/Support/CommandLine.h" 131 using namespace llvm; 132 133 // A handy option for disabling TBAA functionality. The same effect can also be 134 // achieved by stripping the !tbaa tags from IR, but this option is sometimes 135 // more convenient. 136 static cl::opt<bool> EnableTBAA("enable-tbaa", cl::init(true)); 137 138 namespace { 139 /// TBAANode - This is a simple wrapper around an MDNode which provides a 140 /// higher-level interface by hiding the details of how alias analysis 141 /// information is encoded in its operands. 142 class TBAANode { 143 const MDNode *Node; 144 145 public: 146 TBAANode() : Node(nullptr) {} 147 explicit TBAANode(const MDNode *N) : Node(N) {} 148 149 /// getNode - Get the MDNode for this TBAANode. 150 const MDNode *getNode() const { return Node; } 151 152 /// getParent - Get this TBAANode's Alias tree parent. 153 TBAANode getParent() const { 154 if (Node->getNumOperands() < 2) 155 return TBAANode(); 156 MDNode *P = dyn_cast_or_null<MDNode>(Node->getOperand(1)); 157 if (!P) 158 return TBAANode(); 159 // Ok, this node has a valid parent. Return it. 160 return TBAANode(P); 161 } 162 163 /// TypeIsImmutable - Test if this TBAANode represents a type for objects 164 /// which are not modified (by any means) in the context where this 165 /// AliasAnalysis is relevant. 166 bool TypeIsImmutable() const { 167 if (Node->getNumOperands() < 3) 168 return false; 169 ConstantInt *CI = mdconst::dyn_extract<ConstantInt>(Node->getOperand(2)); 170 if (!CI) 171 return false; 172 return CI->getValue()[0]; 173 } 174 }; 175 176 /// This is a simple wrapper around an MDNode which provides a 177 /// higher-level interface by hiding the details of how alias analysis 178 /// information is encoded in its operands. 179 class TBAAStructTagNode { 180 /// This node should be created with createTBAAStructTagNode. 181 const MDNode *Node; 182 183 public: 184 explicit TBAAStructTagNode(const MDNode *N) : Node(N) {} 185 186 /// Get the MDNode for this TBAAStructTagNode. 187 const MDNode *getNode() const { return Node; } 188 189 const MDNode *getBaseType() const { 190 return dyn_cast_or_null<MDNode>(Node->getOperand(0)); 191 } 192 const MDNode *getAccessType() const { 193 return dyn_cast_or_null<MDNode>(Node->getOperand(1)); 194 } 195 uint64_t getOffset() const { 196 return mdconst::extract<ConstantInt>(Node->getOperand(2))->getZExtValue(); 197 } 198 /// TypeIsImmutable - Test if this TBAAStructTagNode represents a type for 199 /// objects which are not modified (by any means) in the context where this 200 /// AliasAnalysis is relevant. 201 bool TypeIsImmutable() const { 202 if (Node->getNumOperands() < 4) 203 return false; 204 ConstantInt *CI = mdconst::dyn_extract<ConstantInt>(Node->getOperand(3)); 205 if (!CI) 206 return false; 207 return CI->getValue()[0]; 208 } 209 }; 210 211 /// This is a simple wrapper around an MDNode which provides a 212 /// higher-level interface by hiding the details of how alias analysis 213 /// information is encoded in its operands. 214 class TBAAStructTypeNode { 215 /// This node should be created with createTBAAStructTypeNode. 216 const MDNode *Node; 217 218 public: 219 TBAAStructTypeNode() : Node(nullptr) {} 220 explicit TBAAStructTypeNode(const MDNode *N) : Node(N) {} 221 222 /// Get the MDNode for this TBAAStructTypeNode. 223 const MDNode *getNode() const { return Node; } 224 225 /// Get this TBAAStructTypeNode's field in the type DAG with 226 /// given offset. Update the offset to be relative to the field type. 227 TBAAStructTypeNode getParent(uint64_t &Offset) const { 228 // Parent can be omitted for the root node. 229 if (Node->getNumOperands() < 2) 230 return TBAAStructTypeNode(); 231 232 // Fast path for a scalar type node and a struct type node with a single 233 // field. 234 if (Node->getNumOperands() <= 3) { 235 uint64_t Cur = Node->getNumOperands() == 2 236 ? 0 237 : mdconst::extract<ConstantInt>(Node->getOperand(2)) 238 ->getZExtValue(); 239 Offset -= Cur; 240 MDNode *P = dyn_cast_or_null<MDNode>(Node->getOperand(1)); 241 if (!P) 242 return TBAAStructTypeNode(); 243 return TBAAStructTypeNode(P); 244 } 245 246 // Assume the offsets are in order. We return the previous field if 247 // the current offset is bigger than the given offset. 248 unsigned TheIdx = 0; 249 for (unsigned Idx = 1; Idx < Node->getNumOperands(); Idx += 2) { 250 uint64_t Cur = mdconst::extract<ConstantInt>(Node->getOperand(Idx + 1)) 251 ->getZExtValue(); 252 if (Cur > Offset) { 253 assert(Idx >= 3 && 254 "TBAAStructTypeNode::getParent should have an offset match!"); 255 TheIdx = Idx - 2; 256 break; 257 } 258 } 259 // Move along the last field. 260 if (TheIdx == 0) 261 TheIdx = Node->getNumOperands() - 2; 262 uint64_t Cur = mdconst::extract<ConstantInt>(Node->getOperand(TheIdx + 1)) 263 ->getZExtValue(); 264 Offset -= Cur; 265 MDNode *P = dyn_cast_or_null<MDNode>(Node->getOperand(TheIdx)); 266 if (!P) 267 return TBAAStructTypeNode(); 268 return TBAAStructTypeNode(P); 269 } 270 }; 271 } 272 273 /// Check the first operand of the tbaa tag node, if it is a MDNode, we treat 274 /// it as struct-path aware TBAA format, otherwise, we treat it as scalar TBAA 275 /// format. 276 static bool isStructPathTBAA(const MDNode *MD) { 277 // Anonymous TBAA root starts with a MDNode and dragonegg uses it as 278 // a TBAA tag. 279 return isa<MDNode>(MD->getOperand(0)) && MD->getNumOperands() >= 3; 280 } 281 282 AliasResult TypeBasedAAResult::alias(const MemoryLocation &LocA, 283 const MemoryLocation &LocB) { 284 if (!EnableTBAA) 285 return AAResultBase::alias(LocA, LocB); 286 287 // Get the attached MDNodes. If either value lacks a tbaa MDNode, we must 288 // be conservative. 289 const MDNode *AM = LocA.AATags.TBAA; 290 if (!AM) 291 return AAResultBase::alias(LocA, LocB); 292 const MDNode *BM = LocB.AATags.TBAA; 293 if (!BM) 294 return AAResultBase::alias(LocA, LocB); 295 296 // If they may alias, chain to the next AliasAnalysis. 297 if (Aliases(AM, BM)) 298 return AAResultBase::alias(LocA, LocB); 299 300 // Otherwise return a definitive result. 301 return NoAlias; 302 } 303 304 bool TypeBasedAAResult::pointsToConstantMemory(const MemoryLocation &Loc, 305 bool OrLocal) { 306 if (!EnableTBAA) 307 return AAResultBase::pointsToConstantMemory(Loc, OrLocal); 308 309 const MDNode *M = Loc.AATags.TBAA; 310 if (!M) 311 return AAResultBase::pointsToConstantMemory(Loc, OrLocal); 312 313 // If this is an "immutable" type, we can assume the pointer is pointing 314 // to constant memory. 315 if ((!isStructPathTBAA(M) && TBAANode(M).TypeIsImmutable()) || 316 (isStructPathTBAA(M) && TBAAStructTagNode(M).TypeIsImmutable())) 317 return true; 318 319 return AAResultBase::pointsToConstantMemory(Loc, OrLocal); 320 } 321 322 FunctionModRefBehavior 323 TypeBasedAAResult::getModRefBehavior(ImmutableCallSite CS) { 324 if (!EnableTBAA) 325 return AAResultBase::getModRefBehavior(CS); 326 327 FunctionModRefBehavior Min = FMRB_UnknownModRefBehavior; 328 329 // If this is an "immutable" type, we can assume the call doesn't write 330 // to memory. 331 if (const MDNode *M = CS.getInstruction()->getMetadata(LLVMContext::MD_tbaa)) 332 if ((!isStructPathTBAA(M) && TBAANode(M).TypeIsImmutable()) || 333 (isStructPathTBAA(M) && TBAAStructTagNode(M).TypeIsImmutable())) 334 Min = FMRB_OnlyReadsMemory; 335 336 return FunctionModRefBehavior(AAResultBase::getModRefBehavior(CS) & Min); 337 } 338 339 FunctionModRefBehavior TypeBasedAAResult::getModRefBehavior(const Function *F) { 340 // Functions don't have metadata. Just chain to the next implementation. 341 return AAResultBase::getModRefBehavior(F); 342 } 343 344 ModRefInfo TypeBasedAAResult::getModRefInfo(ImmutableCallSite CS, 345 const MemoryLocation &Loc) { 346 if (!EnableTBAA) 347 return AAResultBase::getModRefInfo(CS, Loc); 348 349 if (const MDNode *L = Loc.AATags.TBAA) 350 if (const MDNode *M = 351 CS.getInstruction()->getMetadata(LLVMContext::MD_tbaa)) 352 if (!Aliases(L, M)) 353 return MRI_NoModRef; 354 355 return AAResultBase::getModRefInfo(CS, Loc); 356 } 357 358 ModRefInfo TypeBasedAAResult::getModRefInfo(ImmutableCallSite CS1, 359 ImmutableCallSite CS2) { 360 if (!EnableTBAA) 361 return AAResultBase::getModRefInfo(CS1, CS2); 362 363 if (const MDNode *M1 = 364 CS1.getInstruction()->getMetadata(LLVMContext::MD_tbaa)) 365 if (const MDNode *M2 = 366 CS2.getInstruction()->getMetadata(LLVMContext::MD_tbaa)) 367 if (!Aliases(M1, M2)) 368 return MRI_NoModRef; 369 370 return AAResultBase::getModRefInfo(CS1, CS2); 371 } 372 373 bool MDNode::isTBAAVtableAccess() const { 374 if (!isStructPathTBAA(this)) { 375 if (getNumOperands() < 1) 376 return false; 377 if (MDString *Tag1 = dyn_cast<MDString>(getOperand(0))) { 378 if (Tag1->getString() == "vtable pointer") 379 return true; 380 } 381 return false; 382 } 383 384 // For struct-path aware TBAA, we use the access type of the tag. 385 if (getNumOperands() < 2) 386 return false; 387 MDNode *Tag = cast_or_null<MDNode>(getOperand(1)); 388 if (!Tag) 389 return false; 390 if (MDString *Tag1 = dyn_cast<MDString>(Tag->getOperand(0))) { 391 if (Tag1->getString() == "vtable pointer") 392 return true; 393 } 394 return false; 395 } 396 397 MDNode *MDNode::getMostGenericTBAA(MDNode *A, MDNode *B) { 398 if (!A || !B) 399 return nullptr; 400 401 if (A == B) 402 return A; 403 404 // For struct-path aware TBAA, we use the access type of the tag. 405 bool StructPath = isStructPathTBAA(A) && isStructPathTBAA(B); 406 if (StructPath) { 407 A = cast_or_null<MDNode>(A->getOperand(1)); 408 if (!A) 409 return nullptr; 410 B = cast_or_null<MDNode>(B->getOperand(1)); 411 if (!B) 412 return nullptr; 413 } 414 415 SmallSetVector<MDNode *, 4> PathA; 416 MDNode *T = A; 417 while (T) { 418 if (PathA.count(T)) 419 report_fatal_error("Cycle found in TBAA metadata."); 420 PathA.insert(T); 421 T = T->getNumOperands() >= 2 ? cast_or_null<MDNode>(T->getOperand(1)) 422 : nullptr; 423 } 424 425 SmallSetVector<MDNode *, 4> PathB; 426 T = B; 427 while (T) { 428 if (PathB.count(T)) 429 report_fatal_error("Cycle found in TBAA metadata."); 430 PathB.insert(T); 431 T = T->getNumOperands() >= 2 ? cast_or_null<MDNode>(T->getOperand(1)) 432 : nullptr; 433 } 434 435 int IA = PathA.size() - 1; 436 int IB = PathB.size() - 1; 437 438 MDNode *Ret = nullptr; 439 while (IA >= 0 && IB >= 0) { 440 if (PathA[IA] == PathB[IB]) 441 Ret = PathA[IA]; 442 else 443 break; 444 --IA; 445 --IB; 446 } 447 if (!StructPath) 448 return Ret; 449 450 if (!Ret) 451 return nullptr; 452 // We need to convert from a type node to a tag node. 453 Type *Int64 = IntegerType::get(A->getContext(), 64); 454 Metadata *Ops[3] = {Ret, Ret, 455 ConstantAsMetadata::get(ConstantInt::get(Int64, 0))}; 456 return MDNode::get(A->getContext(), Ops); 457 } 458 459 void Instruction::getAAMetadata(AAMDNodes &N, bool Merge) const { 460 if (Merge) 461 N.TBAA = 462 MDNode::getMostGenericTBAA(N.TBAA, getMetadata(LLVMContext::MD_tbaa)); 463 else 464 N.TBAA = getMetadata(LLVMContext::MD_tbaa); 465 466 if (Merge) 467 N.Scope = MDNode::getMostGenericAliasScope( 468 N.Scope, getMetadata(LLVMContext::MD_alias_scope)); 469 else 470 N.Scope = getMetadata(LLVMContext::MD_alias_scope); 471 472 if (Merge) 473 N.NoAlias = 474 MDNode::intersect(N.NoAlias, getMetadata(LLVMContext::MD_noalias)); 475 else 476 N.NoAlias = getMetadata(LLVMContext::MD_noalias); 477 } 478 479 /// Aliases - Test whether the type represented by A may alias the 480 /// type represented by B. 481 bool TypeBasedAAResult::Aliases(const MDNode *A, const MDNode *B) const { 482 // Make sure that both MDNodes are struct-path aware. 483 if (isStructPathTBAA(A) && isStructPathTBAA(B)) 484 return PathAliases(A, B); 485 486 // Keep track of the root node for A and B. 487 TBAANode RootA, RootB; 488 489 // Climb the tree from A to see if we reach B. 490 for (TBAANode T(A);;) { 491 if (T.getNode() == B) 492 // B is an ancestor of A. 493 return true; 494 495 RootA = T; 496 T = T.getParent(); 497 if (!T.getNode()) 498 break; 499 } 500 501 // Climb the tree from B to see if we reach A. 502 for (TBAANode T(B);;) { 503 if (T.getNode() == A) 504 // A is an ancestor of B. 505 return true; 506 507 RootB = T; 508 T = T.getParent(); 509 if (!T.getNode()) 510 break; 511 } 512 513 // Neither node is an ancestor of the other. 514 515 // If they have different roots, they're part of different potentially 516 // unrelated type systems, so we must be conservative. 517 if (RootA.getNode() != RootB.getNode()) 518 return true; 519 520 // If they have the same root, then we've proved there's no alias. 521 return false; 522 } 523 524 /// Test whether the struct-path tag represented by A may alias the 525 /// struct-path tag represented by B. 526 bool TypeBasedAAResult::PathAliases(const MDNode *A, const MDNode *B) const { 527 // Verify that both input nodes are struct-path aware. 528 assert(isStructPathTBAA(A) && "MDNode A is not struct-path aware."); 529 assert(isStructPathTBAA(B) && "MDNode B is not struct-path aware."); 530 531 // Keep track of the root node for A and B. 532 TBAAStructTypeNode RootA, RootB; 533 TBAAStructTagNode TagA(A), TagB(B); 534 535 // TODO: We need to check if AccessType of TagA encloses AccessType of 536 // TagB to support aggregate AccessType. If yes, return true. 537 538 // Start from the base type of A, follow the edge with the correct offset in 539 // the type DAG and adjust the offset until we reach the base type of B or 540 // until we reach the Root node. 541 // Compare the adjusted offset once we have the same base. 542 543 // Climb the type DAG from base type of A to see if we reach base type of B. 544 const MDNode *BaseA = TagA.getBaseType(); 545 const MDNode *BaseB = TagB.getBaseType(); 546 uint64_t OffsetA = TagA.getOffset(), OffsetB = TagB.getOffset(); 547 for (TBAAStructTypeNode T(BaseA);;) { 548 if (T.getNode() == BaseB) 549 // Base type of A encloses base type of B, check if the offsets match. 550 return OffsetA == OffsetB; 551 552 RootA = T; 553 // Follow the edge with the correct offset, OffsetA will be adjusted to 554 // be relative to the field type. 555 T = T.getParent(OffsetA); 556 if (!T.getNode()) 557 break; 558 } 559 560 // Reset OffsetA and climb the type DAG from base type of B to see if we reach 561 // base type of A. 562 OffsetA = TagA.getOffset(); 563 for (TBAAStructTypeNode T(BaseB);;) { 564 if (T.getNode() == BaseA) 565 // Base type of B encloses base type of A, check if the offsets match. 566 return OffsetA == OffsetB; 567 568 RootB = T; 569 // Follow the edge with the correct offset, OffsetB will be adjusted to 570 // be relative to the field type. 571 T = T.getParent(OffsetB); 572 if (!T.getNode()) 573 break; 574 } 575 576 // Neither node is an ancestor of the other. 577 578 // If they have different roots, they're part of different potentially 579 // unrelated type systems, so we must be conservative. 580 if (RootA.getNode() != RootB.getNode()) 581 return true; 582 583 // If they have the same root, then we've proved there's no alias. 584 return false; 585 } 586 587 TypeBasedAAResult TypeBasedAA::run(Function &F, AnalysisManager<Function> *AM) { 588 return TypeBasedAAResult(AM->getResult<TargetLibraryAnalysis>(F)); 589 } 590 591 char TypeBasedAA::PassID; 592 593 char TypeBasedAAWrapperPass::ID = 0; 594 INITIALIZE_PASS_BEGIN(TypeBasedAAWrapperPass, "tbaa", 595 "Type-Based Alias Analysis", false, true) 596 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass) 597 INITIALIZE_PASS_END(TypeBasedAAWrapperPass, "tbaa", "Type-Based Alias Analysis", 598 false, true) 599 600 ImmutablePass *llvm::createTypeBasedAAWrapperPass() { 601 return new TypeBasedAAWrapperPass(); 602 } 603 604 TypeBasedAAWrapperPass::TypeBasedAAWrapperPass() : ImmutablePass(ID) { 605 initializeTypeBasedAAWrapperPassPass(*PassRegistry::getPassRegistry()); 606 } 607 608 bool TypeBasedAAWrapperPass::doInitialization(Module &M) { 609 Result.reset(new TypeBasedAAResult( 610 getAnalysis<TargetLibraryInfoWrapperPass>().getTLI())); 611 return false; 612 } 613 614 bool TypeBasedAAWrapperPass::doFinalization(Module &M) { 615 Result.reset(); 616 return false; 617 } 618 619 void TypeBasedAAWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const { 620 AU.setPreservesAll(); 621 AU.addRequired<TargetLibraryInfoWrapperPass>(); 622 } 623