CGException.cpp revision e996ffd240f20a1048179d7727a6ee3227261921
1//===--- CGException.cpp - Emit LLVM Code for C++ exceptions --------------===// 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 contains code dealing with C++ exception related code generation. 11// 12//===----------------------------------------------------------------------===// 13 14#include "clang/AST/StmtCXX.h" 15 16#include "llvm/Intrinsics.h" 17#include "llvm/IntrinsicInst.h" 18#include "llvm/Support/CallSite.h" 19 20#include "CGObjCRuntime.h" 21#include "CodeGenFunction.h" 22#include "CGException.h" 23#include "CGCleanup.h" 24#include "TargetInfo.h" 25 26using namespace clang; 27using namespace CodeGen; 28 29static llvm::Constant *getAllocateExceptionFn(CodeGenFunction &CGF) { 30 // void *__cxa_allocate_exception(size_t thrown_size); 31 const llvm::Type *SizeTy = CGF.ConvertType(CGF.getContext().getSizeType()); 32 std::vector<const llvm::Type*> Args(1, SizeTy); 33 34 const llvm::FunctionType *FTy = 35 llvm::FunctionType::get(llvm::Type::getInt8PtrTy(CGF.getLLVMContext()), 36 Args, false); 37 38 return CGF.CGM.CreateRuntimeFunction(FTy, "__cxa_allocate_exception"); 39} 40 41static llvm::Constant *getFreeExceptionFn(CodeGenFunction &CGF) { 42 // void __cxa_free_exception(void *thrown_exception); 43 const llvm::Type *Int8PtrTy = llvm::Type::getInt8PtrTy(CGF.getLLVMContext()); 44 std::vector<const llvm::Type*> Args(1, Int8PtrTy); 45 46 const llvm::FunctionType *FTy = 47 llvm::FunctionType::get(llvm::Type::getVoidTy(CGF.getLLVMContext()), 48 Args, false); 49 50 return CGF.CGM.CreateRuntimeFunction(FTy, "__cxa_free_exception"); 51} 52 53static llvm::Constant *getThrowFn(CodeGenFunction &CGF) { 54 // void __cxa_throw(void *thrown_exception, std::type_info *tinfo, 55 // void (*dest) (void *)); 56 57 const llvm::Type *Int8PtrTy = llvm::Type::getInt8PtrTy(CGF.getLLVMContext()); 58 std::vector<const llvm::Type*> Args(3, Int8PtrTy); 59 60 const llvm::FunctionType *FTy = 61 llvm::FunctionType::get(llvm::Type::getVoidTy(CGF.getLLVMContext()), 62 Args, false); 63 64 return CGF.CGM.CreateRuntimeFunction(FTy, "__cxa_throw"); 65} 66 67static llvm::Constant *getReThrowFn(CodeGenFunction &CGF) { 68 // void __cxa_rethrow(); 69 70 const llvm::FunctionType *FTy = 71 llvm::FunctionType::get(llvm::Type::getVoidTy(CGF.getLLVMContext()), false); 72 73 return CGF.CGM.CreateRuntimeFunction(FTy, "__cxa_rethrow"); 74} 75 76static llvm::Constant *getGetExceptionPtrFn(CodeGenFunction &CGF) { 77 // void *__cxa_get_exception_ptr(void*); 78 const llvm::Type *Int8PtrTy = llvm::Type::getInt8PtrTy(CGF.getLLVMContext()); 79 std::vector<const llvm::Type*> Args(1, Int8PtrTy); 80 81 const llvm::FunctionType *FTy = 82 llvm::FunctionType::get(Int8PtrTy, Args, false); 83 84 return CGF.CGM.CreateRuntimeFunction(FTy, "__cxa_get_exception_ptr"); 85} 86 87static llvm::Constant *getBeginCatchFn(CodeGenFunction &CGF) { 88 // void *__cxa_begin_catch(void*); 89 90 const llvm::Type *Int8PtrTy = llvm::Type::getInt8PtrTy(CGF.getLLVMContext()); 91 std::vector<const llvm::Type*> Args(1, Int8PtrTy); 92 93 const llvm::FunctionType *FTy = 94 llvm::FunctionType::get(Int8PtrTy, Args, false); 95 96 return CGF.CGM.CreateRuntimeFunction(FTy, "__cxa_begin_catch"); 97} 98 99static llvm::Constant *getEndCatchFn(CodeGenFunction &CGF) { 100 // void __cxa_end_catch(); 101 102 const llvm::FunctionType *FTy = 103 llvm::FunctionType::get(llvm::Type::getVoidTy(CGF.getLLVMContext()), false); 104 105 return CGF.CGM.CreateRuntimeFunction(FTy, "__cxa_end_catch"); 106} 107 108static llvm::Constant *getUnexpectedFn(CodeGenFunction &CGF) { 109 // void __cxa_call_unexepcted(void *thrown_exception); 110 111 const llvm::Type *Int8PtrTy = llvm::Type::getInt8PtrTy(CGF.getLLVMContext()); 112 std::vector<const llvm::Type*> Args(1, Int8PtrTy); 113 114 const llvm::FunctionType *FTy = 115 llvm::FunctionType::get(llvm::Type::getVoidTy(CGF.getLLVMContext()), 116 Args, false); 117 118 return CGF.CGM.CreateRuntimeFunction(FTy, "__cxa_call_unexpected"); 119} 120 121llvm::Constant *CodeGenFunction::getUnwindResumeOrRethrowFn() { 122 const llvm::Type *Int8PtrTy = llvm::Type::getInt8PtrTy(getLLVMContext()); 123 std::vector<const llvm::Type*> Args(1, Int8PtrTy); 124 125 const llvm::FunctionType *FTy = 126 llvm::FunctionType::get(llvm::Type::getVoidTy(getLLVMContext()), Args, 127 false); 128 129 if (CGM.getLangOptions().SjLjExceptions) 130 return CGM.CreateRuntimeFunction(FTy, "_Unwind_SjLj_Resume_or_Rethrow"); 131 return CGM.CreateRuntimeFunction(FTy, "_Unwind_Resume_or_Rethrow"); 132} 133 134static llvm::Constant *getTerminateFn(CodeGenFunction &CGF) { 135 // void __terminate(); 136 137 const llvm::FunctionType *FTy = 138 llvm::FunctionType::get(llvm::Type::getVoidTy(CGF.getLLVMContext()), false); 139 140 return CGF.CGM.CreateRuntimeFunction(FTy, 141 CGF.CGM.getLangOptions().CPlusPlus ? "_ZSt9terminatev" : "abort"); 142} 143 144static llvm::Constant *getCatchallRethrowFn(CodeGenFunction &CGF, 145 llvm::StringRef Name) { 146 const llvm::Type *Int8PtrTy = 147 llvm::Type::getInt8PtrTy(CGF.getLLVMContext()); 148 std::vector<const llvm::Type*> Args(1, Int8PtrTy); 149 150 const llvm::Type *VoidTy = llvm::Type::getVoidTy(CGF.getLLVMContext()); 151 const llvm::FunctionType *FTy = llvm::FunctionType::get(VoidTy, Args, false); 152 153 return CGF.CGM.CreateRuntimeFunction(FTy, Name); 154} 155 156const EHPersonality EHPersonality::GNU_C("__gcc_personality_v0"); 157const EHPersonality EHPersonality::GNU_C_SJLJ("__gcc_personality_sj0"); 158const EHPersonality EHPersonality::NeXT_ObjC("__objc_personality_v0"); 159const EHPersonality EHPersonality::GNU_CPlusPlus("__gxx_personality_v0"); 160const EHPersonality EHPersonality::GNU_CPlusPlus_SJLJ("__gxx_personality_sj0"); 161const EHPersonality EHPersonality::GNU_ObjC("__gnu_objc_personality_v0", 162 "objc_exception_throw"); 163 164static const EHPersonality &getCPersonality(const LangOptions &L) { 165 if (L.SjLjExceptions) 166 return EHPersonality::GNU_C_SJLJ; 167 return EHPersonality::GNU_C; 168} 169 170static const EHPersonality &getObjCPersonality(const LangOptions &L) { 171 if (L.NeXTRuntime) { 172 if (L.ObjCNonFragileABI) return EHPersonality::NeXT_ObjC; 173 else return getCPersonality(L); 174 } else { 175 return EHPersonality::GNU_ObjC; 176 } 177} 178 179static const EHPersonality &getCXXPersonality(const LangOptions &L) { 180 if (L.SjLjExceptions) 181 return EHPersonality::GNU_CPlusPlus_SJLJ; 182 else 183 return EHPersonality::GNU_CPlusPlus; 184} 185 186/// Determines the personality function to use when both C++ 187/// and Objective-C exceptions are being caught. 188static const EHPersonality &getObjCXXPersonality(const LangOptions &L) { 189 // The ObjC personality defers to the C++ personality for non-ObjC 190 // handlers. Unlike the C++ case, we use the same personality 191 // function on targets using (backend-driven) SJLJ EH. 192 if (L.NeXTRuntime) { 193 if (L.ObjCNonFragileABI) 194 return EHPersonality::NeXT_ObjC; 195 196 // In the fragile ABI, just use C++ exception handling and hope 197 // they're not doing crazy exception mixing. 198 else 199 return getCXXPersonality(L); 200 } 201 202 // The GNU runtime's personality function inherently doesn't support 203 // mixed EH. Use the C++ personality just to avoid returning null. 204 return getCXXPersonality(L); 205} 206 207const EHPersonality &EHPersonality::get(const LangOptions &L) { 208 if (L.CPlusPlus && L.ObjC1) 209 return getObjCXXPersonality(L); 210 else if (L.CPlusPlus) 211 return getCXXPersonality(L); 212 else if (L.ObjC1) 213 return getObjCPersonality(L); 214 else 215 return getCPersonality(L); 216} 217 218static llvm::Constant *getPersonalityFn(CodeGenModule &CGM, 219 const EHPersonality &Personality) { 220 llvm::Constant *Fn = 221 CGM.CreateRuntimeFunction(llvm::FunctionType::get( 222 llvm::Type::getInt32Ty(CGM.getLLVMContext()), 223 true), 224 Personality.getPersonalityFnName()); 225 return Fn; 226} 227 228static llvm::Constant *getOpaquePersonalityFn(CodeGenModule &CGM, 229 const EHPersonality &Personality) { 230 llvm::Constant *Fn = getPersonalityFn(CGM, Personality); 231 return llvm::ConstantExpr::getBitCast(Fn, CGM.Int8PtrTy); 232} 233 234/// Check whether a personality function could reasonably be swapped 235/// for a C++ personality function. 236static bool PersonalityHasOnlyCXXUses(llvm::Constant *Fn) { 237 for (llvm::Constant::use_iterator 238 I = Fn->use_begin(), E = Fn->use_end(); I != E; ++I) { 239 llvm::User *User = *I; 240 241 // Conditionally white-list bitcasts. 242 if (llvm::ConstantExpr *CE = dyn_cast<llvm::ConstantExpr>(User)) { 243 if (CE->getOpcode() != llvm::Instruction::BitCast) return false; 244 if (!PersonalityHasOnlyCXXUses(CE)) 245 return false; 246 continue; 247 } 248 249 // Otherwise, it has to be a selector call. 250 if (!isa<llvm::EHSelectorInst>(User)) return false; 251 252 llvm::EHSelectorInst *Selector = cast<llvm::EHSelectorInst>(User); 253 for (unsigned I = 2, E = Selector->getNumArgOperands(); I != E; ++I) { 254 // Look for something that would've been returned by the ObjC 255 // runtime's GetEHType() method. 256 llvm::GlobalVariable *GV 257 = dyn_cast<llvm::GlobalVariable>(Selector->getArgOperand(I)); 258 if (!GV) continue; 259 260 // ObjC EH selector entries are always global variables with 261 // names starting like this. 262 if (GV->getName().startswith("OBJC_EHTYPE")) 263 return false; 264 } 265 } 266 267 return true; 268} 269 270/// Try to use the C++ personality function in ObjC++. Not doing this 271/// can cause some incompatibilities with gcc, which is more 272/// aggressive about only using the ObjC++ personality in a function 273/// when it really needs it. 274void CodeGenModule::SimplifyPersonality() { 275 // For now, this is really a Darwin-specific operation. 276 if (Context.Target.getTriple().getOS() != llvm::Triple::Darwin) 277 return; 278 279 // If we're not in ObjC++ -fexceptions, there's nothing to do. 280 if (!Features.CPlusPlus || !Features.ObjC1 || !Features.Exceptions) 281 return; 282 283 const EHPersonality &ObjCXX = EHPersonality::get(Features); 284 const EHPersonality &CXX = getCXXPersonality(Features); 285 if (&ObjCXX == &CXX || 286 ObjCXX.getPersonalityFnName() == CXX.getPersonalityFnName()) 287 return; 288 289 llvm::Function *Fn = 290 getModule().getFunction(ObjCXX.getPersonalityFnName()); 291 292 // Nothing to do if it's unused. 293 if (!Fn || Fn->use_empty()) return; 294 295 // Can't do the optimization if it has non-C++ uses. 296 if (!PersonalityHasOnlyCXXUses(Fn)) return; 297 298 // Create the C++ personality function and kill off the old 299 // function. 300 llvm::Constant *CXXFn = getPersonalityFn(*this, CXX); 301 302 // This can happen if the user is screwing with us. 303 if (Fn->getType() != CXXFn->getType()) return; 304 305 Fn->replaceAllUsesWith(CXXFn); 306 Fn->eraseFromParent(); 307} 308 309/// Returns the value to inject into a selector to indicate the 310/// presence of a catch-all. 311static llvm::Constant *getCatchAllValue(CodeGenFunction &CGF) { 312 // Possibly we should use @llvm.eh.catch.all.value here. 313 return llvm::ConstantPointerNull::get(CGF.Int8PtrTy); 314} 315 316/// Returns the value to inject into a selector to indicate the 317/// presence of a cleanup. 318static llvm::Constant *getCleanupValue(CodeGenFunction &CGF) { 319 return llvm::ConstantInt::get(CGF.Builder.getInt32Ty(), 0); 320} 321 322namespace { 323 /// A cleanup to free the exception object if its initialization 324 /// throws. 325 struct FreeException { 326 static void Emit(CodeGenFunction &CGF, bool forEH, 327 llvm::Value *exn) { 328 CGF.Builder.CreateCall(getFreeExceptionFn(CGF), exn) 329 ->setDoesNotThrow(); 330 } 331 }; 332} 333 334// Emits an exception expression into the given location. This 335// differs from EmitAnyExprToMem only in that, if a final copy-ctor 336// call is required, an exception within that copy ctor causes 337// std::terminate to be invoked. 338static void EmitAnyExprToExn(CodeGenFunction &CGF, const Expr *e, 339 llvm::Value *addr) { 340 // Make sure the exception object is cleaned up if there's an 341 // exception during initialization. 342 CGF.pushFullExprCleanup<FreeException>(EHCleanup, addr); 343 EHScopeStack::stable_iterator cleanup = CGF.EHStack.stable_begin(); 344 345 // __cxa_allocate_exception returns a void*; we need to cast this 346 // to the appropriate type for the object. 347 const llvm::Type *ty = CGF.ConvertTypeForMem(e->getType())->getPointerTo(); 348 llvm::Value *typedAddr = CGF.Builder.CreateBitCast(addr, ty); 349 350 // FIXME: this isn't quite right! If there's a final unelided call 351 // to a copy constructor, then according to [except.terminate]p1 we 352 // must call std::terminate() if that constructor throws, because 353 // technically that copy occurs after the exception expression is 354 // evaluated but before the exception is caught. But the best way 355 // to handle that is to teach EmitAggExpr to do the final copy 356 // differently if it can't be elided. 357 CGF.EmitAnyExprToMem(e, typedAddr, /*Volatile*/ false, /*IsInit*/ true); 358 359 // Deactivate the cleanup block. 360 CGF.DeactivateCleanupBlock(cleanup); 361} 362 363llvm::Value *CodeGenFunction::getExceptionSlot() { 364 if (!ExceptionSlot) { 365 const llvm::Type *i8p = llvm::Type::getInt8PtrTy(getLLVMContext()); 366 ExceptionSlot = CreateTempAlloca(i8p, "exn.slot"); 367 } 368 return ExceptionSlot; 369} 370 371void CodeGenFunction::EmitCXXThrowExpr(const CXXThrowExpr *E) { 372 if (!E->getSubExpr()) { 373 if (getInvokeDest()) { 374 Builder.CreateInvoke(getReThrowFn(*this), 375 getUnreachableBlock(), 376 getInvokeDest()) 377 ->setDoesNotReturn(); 378 } else { 379 Builder.CreateCall(getReThrowFn(*this))->setDoesNotReturn(); 380 Builder.CreateUnreachable(); 381 } 382 383 // throw is an expression, and the expression emitters expect us 384 // to leave ourselves at a valid insertion point. 385 EmitBlock(createBasicBlock("throw.cont")); 386 387 return; 388 } 389 390 QualType ThrowType = E->getSubExpr()->getType(); 391 392 // Now allocate the exception object. 393 const llvm::Type *SizeTy = ConvertType(getContext().getSizeType()); 394 uint64_t TypeSize = getContext().getTypeSizeInChars(ThrowType).getQuantity(); 395 396 llvm::Constant *AllocExceptionFn = getAllocateExceptionFn(*this); 397 llvm::CallInst *ExceptionPtr = 398 Builder.CreateCall(AllocExceptionFn, 399 llvm::ConstantInt::get(SizeTy, TypeSize), 400 "exception"); 401 ExceptionPtr->setDoesNotThrow(); 402 403 EmitAnyExprToExn(*this, E->getSubExpr(), ExceptionPtr); 404 405 // Now throw the exception. 406 const llvm::Type *Int8PtrTy = llvm::Type::getInt8PtrTy(getLLVMContext()); 407 llvm::Constant *TypeInfo = CGM.GetAddrOfRTTIDescriptor(ThrowType, 408 /*ForEH=*/true); 409 410 // The address of the destructor. If the exception type has a 411 // trivial destructor (or isn't a record), we just pass null. 412 llvm::Constant *Dtor = 0; 413 if (const RecordType *RecordTy = ThrowType->getAs<RecordType>()) { 414 CXXRecordDecl *Record = cast<CXXRecordDecl>(RecordTy->getDecl()); 415 if (!Record->hasTrivialDestructor()) { 416 CXXDestructorDecl *DtorD = Record->getDestructor(); 417 Dtor = CGM.GetAddrOfCXXDestructor(DtorD, Dtor_Complete); 418 Dtor = llvm::ConstantExpr::getBitCast(Dtor, Int8PtrTy); 419 } 420 } 421 if (!Dtor) Dtor = llvm::Constant::getNullValue(Int8PtrTy); 422 423 if (getInvokeDest()) { 424 llvm::InvokeInst *ThrowCall = 425 Builder.CreateInvoke3(getThrowFn(*this), 426 getUnreachableBlock(), getInvokeDest(), 427 ExceptionPtr, TypeInfo, Dtor); 428 ThrowCall->setDoesNotReturn(); 429 } else { 430 llvm::CallInst *ThrowCall = 431 Builder.CreateCall3(getThrowFn(*this), ExceptionPtr, TypeInfo, Dtor); 432 ThrowCall->setDoesNotReturn(); 433 Builder.CreateUnreachable(); 434 } 435 436 // throw is an expression, and the expression emitters expect us 437 // to leave ourselves at a valid insertion point. 438 EmitBlock(createBasicBlock("throw.cont")); 439} 440 441void CodeGenFunction::EmitStartEHSpec(const Decl *D) { 442 if (!Exceptions) 443 return; 444 445 const FunctionDecl* FD = dyn_cast_or_null<FunctionDecl>(D); 446 if (FD == 0) 447 return; 448 const FunctionProtoType *Proto = FD->getType()->getAs<FunctionProtoType>(); 449 if (Proto == 0) 450 return; 451 452 assert(!Proto->hasAnyExceptionSpec() && "function with parameter pack"); 453 454 if (!Proto->hasExceptionSpec()) 455 return; 456 457 unsigned NumExceptions = Proto->getNumExceptions(); 458 EHFilterScope *Filter = EHStack.pushFilter(NumExceptions); 459 460 for (unsigned I = 0; I != NumExceptions; ++I) { 461 QualType Ty = Proto->getExceptionType(I); 462 QualType ExceptType = Ty.getNonReferenceType().getUnqualifiedType(); 463 llvm::Value *EHType = CGM.GetAddrOfRTTIDescriptor(ExceptType, 464 /*ForEH=*/true); 465 Filter->setFilter(I, EHType); 466 } 467} 468 469void CodeGenFunction::EmitEndEHSpec(const Decl *D) { 470 if (!Exceptions) 471 return; 472 473 const FunctionDecl* FD = dyn_cast_or_null<FunctionDecl>(D); 474 if (FD == 0) 475 return; 476 const FunctionProtoType *Proto = FD->getType()->getAs<FunctionProtoType>(); 477 if (Proto == 0) 478 return; 479 480 if (!Proto->hasExceptionSpec()) 481 return; 482 483 EHStack.popFilter(); 484} 485 486void CodeGenFunction::EmitCXXTryStmt(const CXXTryStmt &S) { 487 EnterCXXTryStmt(S); 488 EmitStmt(S.getTryBlock()); 489 ExitCXXTryStmt(S); 490} 491 492void CodeGenFunction::EnterCXXTryStmt(const CXXTryStmt &S, bool IsFnTryBlock) { 493 unsigned NumHandlers = S.getNumHandlers(); 494 EHCatchScope *CatchScope = EHStack.pushCatch(NumHandlers); 495 496 for (unsigned I = 0; I != NumHandlers; ++I) { 497 const CXXCatchStmt *C = S.getHandler(I); 498 499 llvm::BasicBlock *Handler = createBasicBlock("catch"); 500 if (C->getExceptionDecl()) { 501 // FIXME: Dropping the reference type on the type into makes it 502 // impossible to correctly implement catch-by-reference 503 // semantics for pointers. Unfortunately, this is what all 504 // existing compilers do, and it's not clear that the standard 505 // personality routine is capable of doing this right. See C++ DR 388: 506 // http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_active.html#388 507 QualType CaughtType = C->getCaughtType(); 508 CaughtType = CaughtType.getNonReferenceType().getUnqualifiedType(); 509 510 llvm::Value *TypeInfo = 0; 511 if (CaughtType->isObjCObjectPointerType()) 512 TypeInfo = CGM.getObjCRuntime().GetEHType(CaughtType); 513 else 514 TypeInfo = CGM.GetAddrOfRTTIDescriptor(CaughtType, /*ForEH=*/true); 515 CatchScope->setHandler(I, TypeInfo, Handler); 516 } else { 517 // No exception decl indicates '...', a catch-all. 518 CatchScope->setCatchAllHandler(I, Handler); 519 } 520 } 521} 522 523/// Check whether this is a non-EH scope, i.e. a scope which doesn't 524/// affect exception handling. Currently, the only non-EH scopes are 525/// normal-only cleanup scopes. 526static bool isNonEHScope(const EHScope &S) { 527 switch (S.getKind()) { 528 case EHScope::Cleanup: 529 return !cast<EHCleanupScope>(S).isEHCleanup(); 530 case EHScope::Filter: 531 case EHScope::Catch: 532 case EHScope::Terminate: 533 return false; 534 } 535 536 // Suppress warning. 537 return false; 538} 539 540llvm::BasicBlock *CodeGenFunction::getInvokeDestImpl() { 541 assert(EHStack.requiresLandingPad()); 542 assert(!EHStack.empty()); 543 544 if (!Exceptions) 545 return 0; 546 547 // Check the innermost scope for a cached landing pad. If this is 548 // a non-EH cleanup, we'll check enclosing scopes in EmitLandingPad. 549 llvm::BasicBlock *LP = EHStack.begin()->getCachedLandingPad(); 550 if (LP) return LP; 551 552 // Build the landing pad for this scope. 553 LP = EmitLandingPad(); 554 assert(LP); 555 556 // Cache the landing pad on the innermost scope. If this is a 557 // non-EH scope, cache the landing pad on the enclosing scope, too. 558 for (EHScopeStack::iterator ir = EHStack.begin(); true; ++ir) { 559 ir->setCachedLandingPad(LP); 560 if (!isNonEHScope(*ir)) break; 561 } 562 563 return LP; 564} 565 566llvm::BasicBlock *CodeGenFunction::EmitLandingPad() { 567 assert(EHStack.requiresLandingPad()); 568 569 // This function contains a hack to work around a design flaw in 570 // LLVM's EH IR which breaks semantics after inlining. This same 571 // hack is implemented in llvm-gcc. 572 // 573 // The LLVM EH abstraction is basically a thin veneer over the 574 // traditional GCC zero-cost design: for each range of instructions 575 // in the function, there is (at most) one "landing pad" with an 576 // associated chain of EH actions. A language-specific personality 577 // function interprets this chain of actions and (1) decides whether 578 // or not to resume execution at the landing pad and (2) if so, 579 // provides an integer indicating why it's stopping. In LLVM IR, 580 // the association of a landing pad with a range of instructions is 581 // achieved via an invoke instruction, the chain of actions becomes 582 // the arguments to the @llvm.eh.selector call, and the selector 583 // call returns the integer indicator. Other than the required 584 // presence of two intrinsic function calls in the landing pad, 585 // the IR exactly describes the layout of the output code. 586 // 587 // A principal advantage of this design is that it is completely 588 // language-agnostic; in theory, the LLVM optimizers can treat 589 // landing pads neutrally, and targets need only know how to lower 590 // the intrinsics to have a functioning exceptions system (assuming 591 // that platform exceptions follow something approximately like the 592 // GCC design). Unfortunately, landing pads cannot be combined in a 593 // language-agnostic way: given selectors A and B, there is no way 594 // to make a single landing pad which faithfully represents the 595 // semantics of propagating an exception first through A, then 596 // through B, without knowing how the personality will interpret the 597 // (lowered form of the) selectors. This means that inlining has no 598 // choice but to crudely chain invokes (i.e., to ignore invokes in 599 // the inlined function, but to turn all unwindable calls into 600 // invokes), which is only semantically valid if every unwind stops 601 // at every landing pad. 602 // 603 // Therefore, the invoke-inline hack is to guarantee that every 604 // landing pad has a catch-all. 605 const bool UseInvokeInlineHack = true; 606 607 for (EHScopeStack::iterator ir = EHStack.begin(); ; ) { 608 assert(ir != EHStack.end() && 609 "stack requiring landing pad is nothing but non-EH scopes?"); 610 611 // If this is a terminate scope, just use the singleton terminate 612 // landing pad. 613 if (isa<EHTerminateScope>(*ir)) 614 return getTerminateLandingPad(); 615 616 // If this isn't an EH scope, iterate; otherwise break out. 617 if (!isNonEHScope(*ir)) break; 618 ++ir; 619 620 // We haven't checked this scope for a cached landing pad yet. 621 if (llvm::BasicBlock *LP = ir->getCachedLandingPad()) 622 return LP; 623 } 624 625 // Save the current IR generation state. 626 CGBuilderTy::InsertPoint SavedIP = Builder.saveAndClearIP(); 627 628 const EHPersonality &Personality = EHPersonality::get(getLangOptions()); 629 630 // Create and configure the landing pad. 631 llvm::BasicBlock *LP = createBasicBlock("lpad"); 632 EmitBlock(LP); 633 634 // Save the exception pointer. It's safe to use a single exception 635 // pointer per function because EH cleanups can never have nested 636 // try/catches. 637 llvm::CallInst *Exn = 638 Builder.CreateCall(CGM.getIntrinsic(llvm::Intrinsic::eh_exception), "exn"); 639 Exn->setDoesNotThrow(); 640 Builder.CreateStore(Exn, getExceptionSlot()); 641 642 // Build the selector arguments. 643 llvm::SmallVector<llvm::Value*, 8> EHSelector; 644 EHSelector.push_back(Exn); 645 EHSelector.push_back(getOpaquePersonalityFn(CGM, Personality)); 646 647 // Accumulate all the handlers in scope. 648 llvm::DenseMap<llvm::Value*, UnwindDest> EHHandlers; 649 UnwindDest CatchAll; 650 bool HasEHCleanup = false; 651 bool HasEHFilter = false; 652 llvm::SmallVector<llvm::Value*, 8> EHFilters; 653 for (EHScopeStack::iterator I = EHStack.begin(), E = EHStack.end(); 654 I != E; ++I) { 655 656 switch (I->getKind()) { 657 case EHScope::Cleanup: 658 if (!HasEHCleanup) 659 HasEHCleanup = cast<EHCleanupScope>(*I).isEHCleanup(); 660 // We otherwise don't care about cleanups. 661 continue; 662 663 case EHScope::Filter: { 664 assert(I.next() == EHStack.end() && "EH filter is not end of EH stack"); 665 assert(!CatchAll.isValid() && "EH filter reached after catch-all"); 666 667 // Filter scopes get added to the selector in wierd ways. 668 EHFilterScope &Filter = cast<EHFilterScope>(*I); 669 HasEHFilter = true; 670 671 // Add all the filter values which we aren't already explicitly 672 // catching. 673 for (unsigned I = 0, E = Filter.getNumFilters(); I != E; ++I) { 674 llvm::Value *FV = Filter.getFilter(I); 675 if (!EHHandlers.count(FV)) 676 EHFilters.push_back(FV); 677 } 678 goto done; 679 } 680 681 case EHScope::Terminate: 682 // Terminate scopes are basically catch-alls. 683 assert(!CatchAll.isValid()); 684 CatchAll = UnwindDest(getTerminateHandler(), 685 EHStack.getEnclosingEHCleanup(I), 686 cast<EHTerminateScope>(*I).getDestIndex()); 687 goto done; 688 689 case EHScope::Catch: 690 break; 691 } 692 693 EHCatchScope &Catch = cast<EHCatchScope>(*I); 694 for (unsigned HI = 0, HE = Catch.getNumHandlers(); HI != HE; ++HI) { 695 EHCatchScope::Handler Handler = Catch.getHandler(HI); 696 697 // Catch-all. We should only have one of these per catch. 698 if (!Handler.Type) { 699 assert(!CatchAll.isValid()); 700 CatchAll = UnwindDest(Handler.Block, 701 EHStack.getEnclosingEHCleanup(I), 702 Handler.Index); 703 continue; 704 } 705 706 // Check whether we already have a handler for this type. 707 UnwindDest &Dest = EHHandlers[Handler.Type]; 708 if (Dest.isValid()) continue; 709 710 EHSelector.push_back(Handler.Type); 711 Dest = UnwindDest(Handler.Block, 712 EHStack.getEnclosingEHCleanup(I), 713 Handler.Index); 714 } 715 716 // Stop if we found a catch-all. 717 if (CatchAll.isValid()) break; 718 } 719 720 done: 721 unsigned LastToEmitInLoop = EHSelector.size(); 722 723 // If we have a catch-all, add null to the selector. 724 if (CatchAll.isValid()) { 725 EHSelector.push_back(getCatchAllValue(*this)); 726 727 // If we have an EH filter, we need to add those handlers in the 728 // right place in the selector, which is to say, at the end. 729 } else if (HasEHFilter) { 730 // Create a filter expression: an integer constant saying how many 731 // filters there are (+1 to avoid ambiguity with 0 for cleanup), 732 // followed by the filter types. The personality routine only 733 // lands here if the filter doesn't match. 734 EHSelector.push_back(llvm::ConstantInt::get(Builder.getInt32Ty(), 735 EHFilters.size() + 1)); 736 EHSelector.append(EHFilters.begin(), EHFilters.end()); 737 738 // Also check whether we need a cleanup. 739 if (UseInvokeInlineHack || HasEHCleanup) 740 EHSelector.push_back(UseInvokeInlineHack 741 ? getCatchAllValue(*this) 742 : getCleanupValue(*this)); 743 744 // Otherwise, signal that we at least have cleanups. 745 } else if (UseInvokeInlineHack || HasEHCleanup) { 746 EHSelector.push_back(UseInvokeInlineHack 747 ? getCatchAllValue(*this) 748 : getCleanupValue(*this)); 749 } else { 750 assert(LastToEmitInLoop > 2); 751 LastToEmitInLoop--; 752 } 753 754 assert(EHSelector.size() >= 3 && "selector call has only two arguments!"); 755 756 // Tell the backend how to generate the landing pad. 757 llvm::CallInst *Selection = 758 Builder.CreateCall(CGM.getIntrinsic(llvm::Intrinsic::eh_selector), 759 EHSelector.begin(), EHSelector.end(), "eh.selector"); 760 Selection->setDoesNotThrow(); 761 762 // Select the right handler. 763 llvm::Value *llvm_eh_typeid_for = 764 CGM.getIntrinsic(llvm::Intrinsic::eh_typeid_for); 765 766 // The results of llvm_eh_typeid_for aren't reliable --- at least 767 // not locally --- so we basically have to do this as an 'if' chain. 768 // We walk through the first N-1 catch clauses, testing and chaining, 769 // and then fall into the final clause (which is either a cleanup, a 770 // filter (possibly with a cleanup), a catch-all, or another catch). 771 for (unsigned I = 2; I != LastToEmitInLoop; ++I) { 772 llvm::Value *Type = EHSelector[I]; 773 UnwindDest Dest = EHHandlers[Type]; 774 assert(Dest.isValid() && "no handler entry for value in selector?"); 775 776 // Figure out where to branch on a match. As a debug code-size 777 // optimization, if the scope depth matches the innermost cleanup, 778 // we branch directly to the catch handler. 779 llvm::BasicBlock *Match = Dest.getBlock(); 780 bool MatchNeedsCleanup = 781 Dest.getScopeDepth() != EHStack.getInnermostEHCleanup(); 782 if (MatchNeedsCleanup) 783 Match = createBasicBlock("eh.match"); 784 785 llvm::BasicBlock *Next = createBasicBlock("eh.next"); 786 787 // Check whether the exception matches. 788 llvm::CallInst *Id 789 = Builder.CreateCall(llvm_eh_typeid_for, 790 Builder.CreateBitCast(Type, Int8PtrTy)); 791 Id->setDoesNotThrow(); 792 Builder.CreateCondBr(Builder.CreateICmpEQ(Selection, Id), 793 Match, Next); 794 795 // Emit match code if necessary. 796 if (MatchNeedsCleanup) { 797 EmitBlock(Match); 798 EmitBranchThroughEHCleanup(Dest); 799 } 800 801 // Continue to the next match. 802 EmitBlock(Next); 803 } 804 805 // Emit the final case in the selector. 806 // This might be a catch-all.... 807 if (CatchAll.isValid()) { 808 assert(isa<llvm::ConstantPointerNull>(EHSelector.back())); 809 EmitBranchThroughEHCleanup(CatchAll); 810 811 // ...or an EH filter... 812 } else if (HasEHFilter) { 813 llvm::Value *SavedSelection = Selection; 814 815 // First, unwind out to the outermost scope if necessary. 816 if (EHStack.hasEHCleanups()) { 817 // The end here might not dominate the beginning, so we might need to 818 // save the selector if we need it. 819 llvm::AllocaInst *SelectorVar = 0; 820 if (HasEHCleanup) { 821 SelectorVar = CreateTempAlloca(Builder.getInt32Ty(), "selector.var"); 822 Builder.CreateStore(Selection, SelectorVar); 823 } 824 825 llvm::BasicBlock *CleanupContBB = createBasicBlock("ehspec.cleanup.cont"); 826 EmitBranchThroughEHCleanup(UnwindDest(CleanupContBB, EHStack.stable_end(), 827 EHStack.getNextEHDestIndex())); 828 EmitBlock(CleanupContBB); 829 830 if (HasEHCleanup) 831 SavedSelection = Builder.CreateLoad(SelectorVar, "ehspec.saved-selector"); 832 } 833 834 // If there was a cleanup, we'll need to actually check whether we 835 // landed here because the filter triggered. 836 if (UseInvokeInlineHack || HasEHCleanup) { 837 llvm::BasicBlock *RethrowBB = createBasicBlock("cleanup"); 838 llvm::BasicBlock *UnexpectedBB = createBasicBlock("ehspec.unexpected"); 839 840 llvm::Constant *Zero = llvm::ConstantInt::get(Builder.getInt32Ty(), 0); 841 llvm::Value *FailsFilter = 842 Builder.CreateICmpSLT(SavedSelection, Zero, "ehspec.fails"); 843 Builder.CreateCondBr(FailsFilter, UnexpectedBB, RethrowBB); 844 845 // The rethrow block is where we land if this was a cleanup. 846 // TODO: can this be _Unwind_Resume if the InvokeInlineHack is off? 847 EmitBlock(RethrowBB); 848 Builder.CreateCall(getUnwindResumeOrRethrowFn(), 849 Builder.CreateLoad(getExceptionSlot())) 850 ->setDoesNotReturn(); 851 Builder.CreateUnreachable(); 852 853 EmitBlock(UnexpectedBB); 854 } 855 856 // Call __cxa_call_unexpected. This doesn't need to be an invoke 857 // because __cxa_call_unexpected magically filters exceptions 858 // according to the last landing pad the exception was thrown 859 // into. Seriously. 860 Builder.CreateCall(getUnexpectedFn(*this), 861 Builder.CreateLoad(getExceptionSlot())) 862 ->setDoesNotReturn(); 863 Builder.CreateUnreachable(); 864 865 // ...or a normal catch handler... 866 } else if (!UseInvokeInlineHack && !HasEHCleanup) { 867 llvm::Value *Type = EHSelector.back(); 868 EmitBranchThroughEHCleanup(EHHandlers[Type]); 869 870 // ...or a cleanup. 871 } else { 872 EmitBranchThroughEHCleanup(getRethrowDest()); 873 } 874 875 // Restore the old IR generation state. 876 Builder.restoreIP(SavedIP); 877 878 return LP; 879} 880 881namespace { 882 /// A cleanup to call __cxa_end_catch. In many cases, the caught 883 /// exception type lets us state definitively that the thrown exception 884 /// type does not have a destructor. In particular: 885 /// - Catch-alls tell us nothing, so we have to conservatively 886 /// assume that the thrown exception might have a destructor. 887 /// - Catches by reference behave according to their base types. 888 /// - Catches of non-record types will only trigger for exceptions 889 /// of non-record types, which never have destructors. 890 /// - Catches of record types can trigger for arbitrary subclasses 891 /// of the caught type, so we have to assume the actual thrown 892 /// exception type might have a throwing destructor, even if the 893 /// caught type's destructor is trivial or nothrow. 894 struct CallEndCatch : EHScopeStack::Cleanup { 895 CallEndCatch(bool MightThrow) : MightThrow(MightThrow) {} 896 bool MightThrow; 897 898 void Emit(CodeGenFunction &CGF, bool IsForEH) { 899 if (!MightThrow) { 900 CGF.Builder.CreateCall(getEndCatchFn(CGF))->setDoesNotThrow(); 901 return; 902 } 903 904 CGF.EmitCallOrInvoke(getEndCatchFn(CGF), 0, 0); 905 } 906 }; 907} 908 909/// Emits a call to __cxa_begin_catch and enters a cleanup to call 910/// __cxa_end_catch. 911/// 912/// \param EndMightThrow - true if __cxa_end_catch might throw 913static llvm::Value *CallBeginCatch(CodeGenFunction &CGF, 914 llvm::Value *Exn, 915 bool EndMightThrow) { 916 llvm::CallInst *Call = CGF.Builder.CreateCall(getBeginCatchFn(CGF), Exn); 917 Call->setDoesNotThrow(); 918 919 CGF.EHStack.pushCleanup<CallEndCatch>(NormalAndEHCleanup, EndMightThrow); 920 921 return Call; 922} 923 924/// A "special initializer" callback for initializing a catch 925/// parameter during catch initialization. 926static void InitCatchParam(CodeGenFunction &CGF, 927 const VarDecl &CatchParam, 928 llvm::Value *ParamAddr) { 929 // Load the exception from where the landing pad saved it. 930 llvm::Value *Exn = CGF.Builder.CreateLoad(CGF.getExceptionSlot(), "exn"); 931 932 CanQualType CatchType = 933 CGF.CGM.getContext().getCanonicalType(CatchParam.getType()); 934 const llvm::Type *LLVMCatchTy = CGF.ConvertTypeForMem(CatchType); 935 936 // If we're catching by reference, we can just cast the object 937 // pointer to the appropriate pointer. 938 if (isa<ReferenceType>(CatchType)) { 939 QualType CaughtType = cast<ReferenceType>(CatchType)->getPointeeType(); 940 bool EndCatchMightThrow = CaughtType->isRecordType(); 941 942 // __cxa_begin_catch returns the adjusted object pointer. 943 llvm::Value *AdjustedExn = CallBeginCatch(CGF, Exn, EndCatchMightThrow); 944 945 // We have no way to tell the personality function that we're 946 // catching by reference, so if we're catching a pointer, 947 // __cxa_begin_catch will actually return that pointer by value. 948 if (const PointerType *PT = dyn_cast<PointerType>(CaughtType)) { 949 QualType PointeeType = PT->getPointeeType(); 950 951 // When catching by reference, generally we should just ignore 952 // this by-value pointer and use the exception object instead. 953 if (!PointeeType->isRecordType()) { 954 955 // Exn points to the struct _Unwind_Exception header, which 956 // we have to skip past in order to reach the exception data. 957 unsigned HeaderSize = 958 CGF.CGM.getTargetCodeGenInfo().getSizeOfUnwindException(); 959 AdjustedExn = CGF.Builder.CreateConstGEP1_32(Exn, HeaderSize); 960 961 // However, if we're catching a pointer-to-record type that won't 962 // work, because the personality function might have adjusted 963 // the pointer. There's actually no way for us to fully satisfy 964 // the language/ABI contract here: we can't use Exn because it 965 // might have the wrong adjustment, but we can't use the by-value 966 // pointer because it's off by a level of abstraction. 967 // 968 // The current solution is to dump the adjusted pointer into an 969 // alloca, which breaks language semantics (because changing the 970 // pointer doesn't change the exception) but at least works. 971 // The better solution would be to filter out non-exact matches 972 // and rethrow them, but this is tricky because the rethrow 973 // really needs to be catchable by other sites at this landing 974 // pad. The best solution is to fix the personality function. 975 } else { 976 // Pull the pointer for the reference type off. 977 const llvm::Type *PtrTy = 978 cast<llvm::PointerType>(LLVMCatchTy)->getElementType(); 979 980 // Create the temporary and write the adjusted pointer into it. 981 llvm::Value *ExnPtrTmp = CGF.CreateTempAlloca(PtrTy, "exn.byref.tmp"); 982 llvm::Value *Casted = CGF.Builder.CreateBitCast(AdjustedExn, PtrTy); 983 CGF.Builder.CreateStore(Casted, ExnPtrTmp); 984 985 // Bind the reference to the temporary. 986 AdjustedExn = ExnPtrTmp; 987 } 988 } 989 990 llvm::Value *ExnCast = 991 CGF.Builder.CreateBitCast(AdjustedExn, LLVMCatchTy, "exn.byref"); 992 CGF.Builder.CreateStore(ExnCast, ParamAddr); 993 return; 994 } 995 996 // Non-aggregates (plus complexes). 997 bool IsComplex = false; 998 if (!CGF.hasAggregateLLVMType(CatchType) || 999 (IsComplex = CatchType->isAnyComplexType())) { 1000 llvm::Value *AdjustedExn = CallBeginCatch(CGF, Exn, false); 1001 1002 // If the catch type is a pointer type, __cxa_begin_catch returns 1003 // the pointer by value. 1004 if (CatchType->hasPointerRepresentation()) { 1005 llvm::Value *CastExn = 1006 CGF.Builder.CreateBitCast(AdjustedExn, LLVMCatchTy, "exn.casted"); 1007 CGF.Builder.CreateStore(CastExn, ParamAddr); 1008 return; 1009 } 1010 1011 // Otherwise, it returns a pointer into the exception object. 1012 1013 const llvm::Type *PtrTy = LLVMCatchTy->getPointerTo(0); // addrspace 0 ok 1014 llvm::Value *Cast = CGF.Builder.CreateBitCast(AdjustedExn, PtrTy); 1015 1016 if (IsComplex) { 1017 CGF.StoreComplexToAddr(CGF.LoadComplexFromAddr(Cast, /*volatile*/ false), 1018 ParamAddr, /*volatile*/ false); 1019 } else { 1020 unsigned Alignment = 1021 CGF.getContext().getDeclAlign(&CatchParam).getQuantity(); 1022 llvm::Value *ExnLoad = CGF.Builder.CreateLoad(Cast, "exn.scalar"); 1023 CGF.EmitStoreOfScalar(ExnLoad, ParamAddr, /*volatile*/ false, Alignment, 1024 CatchType); 1025 } 1026 return; 1027 } 1028 1029 // FIXME: this *really* needs to be done via a proper, Sema-emitted 1030 // initializer expression. 1031 1032 CXXRecordDecl *RD = CatchType.getTypePtr()->getAsCXXRecordDecl(); 1033 assert(RD && "aggregate catch type was not a record!"); 1034 1035 const llvm::Type *PtrTy = LLVMCatchTy->getPointerTo(0); // addrspace 0 ok 1036 1037 const Expr *copyExpr = CatchParam.getInit(); 1038 if (!copyExpr) { 1039 llvm::Value *AdjustedExn = CallBeginCatch(CGF, Exn, true); 1040 llvm::Value *Cast = CGF.Builder.CreateBitCast(AdjustedExn, PtrTy); 1041 CGF.EmitAggregateCopy(ParamAddr, Cast, CatchType); 1042 return; 1043 } 1044 1045 // We have to call __cxa_get_exception_ptr to get the adjusted 1046 // pointer before copying. 1047 llvm::CallInst *rawAdjustedExn = 1048 CGF.Builder.CreateCall(getGetExceptionPtrFn(CGF), Exn); 1049 rawAdjustedExn->setDoesNotThrow(); 1050 1051 // Cast that to the appropriate type. 1052 llvm::Value *adjustedExn = CGF.Builder.CreateBitCast(rawAdjustedExn, PtrTy); 1053 1054 // The copy expression is defined in terms of an OpaqueValueExpr. 1055 // Find it and map it to the adjusted expression. 1056 CodeGenFunction::OpaqueValueMapping 1057 opaque(CGF, OpaqueValueExpr::findInCopyConstruct(copyExpr), adjustedExn); 1058 1059 // Call the copy ctor in a terminate scope. 1060 CGF.EHStack.pushTerminate(); 1061 1062 // Perform the copy construction. 1063 CGF.EmitAggExpr(copyExpr, AggValueSlot::forAddr(ParamAddr, false, false)); 1064 1065 // Leave the terminate scope. 1066 CGF.EHStack.popTerminate(); 1067 1068 // Undo the opaque value mapping. 1069 opaque.pop(); 1070 1071 // Finally we can call __cxa_begin_catch. 1072 CallBeginCatch(CGF, Exn, true); 1073} 1074 1075/// Begins a catch statement by initializing the catch variable and 1076/// calling __cxa_begin_catch. 1077static void BeginCatch(CodeGenFunction &CGF, const CXXCatchStmt *S) { 1078 // We have to be very careful with the ordering of cleanups here: 1079 // C++ [except.throw]p4: 1080 // The destruction [of the exception temporary] occurs 1081 // immediately after the destruction of the object declared in 1082 // the exception-declaration in the handler. 1083 // 1084 // So the precise ordering is: 1085 // 1. Construct catch variable. 1086 // 2. __cxa_begin_catch 1087 // 3. Enter __cxa_end_catch cleanup 1088 // 4. Enter dtor cleanup 1089 // 1090 // We do this by initializing the exception variable with a 1091 // "special initializer", InitCatchParam. Delegation sequence: 1092 // - ExitCXXTryStmt opens a RunCleanupsScope 1093 // - EmitLocalBlockVarDecl creates the variable and debug info 1094 // - InitCatchParam initializes the variable from the exception 1095 // - CallBeginCatch calls __cxa_begin_catch 1096 // - CallBeginCatch enters the __cxa_end_catch cleanup 1097 // - EmitLocalBlockVarDecl enters the variable destructor cleanup 1098 // - EmitCXXTryStmt emits the code for the catch body 1099 // - EmitCXXTryStmt close the RunCleanupsScope 1100 1101 VarDecl *CatchParam = S->getExceptionDecl(); 1102 if (!CatchParam) { 1103 llvm::Value *Exn = CGF.Builder.CreateLoad(CGF.getExceptionSlot(), "exn"); 1104 CallBeginCatch(CGF, Exn, true); 1105 return; 1106 } 1107 1108 // Emit the local. 1109 CGF.EmitAutoVarDecl(*CatchParam, &InitCatchParam); 1110} 1111 1112namespace { 1113 struct CallRethrow : EHScopeStack::Cleanup { 1114 void Emit(CodeGenFunction &CGF, bool IsForEH) { 1115 CGF.EmitCallOrInvoke(getReThrowFn(CGF), 0, 0); 1116 } 1117 }; 1118} 1119 1120void CodeGenFunction::ExitCXXTryStmt(const CXXTryStmt &S, bool IsFnTryBlock) { 1121 unsigned NumHandlers = S.getNumHandlers(); 1122 EHCatchScope &CatchScope = cast<EHCatchScope>(*EHStack.begin()); 1123 assert(CatchScope.getNumHandlers() == NumHandlers); 1124 1125 // Copy the handler blocks off before we pop the EH stack. Emitting 1126 // the handlers might scribble on this memory. 1127 llvm::SmallVector<EHCatchScope::Handler, 8> Handlers(NumHandlers); 1128 memcpy(Handlers.data(), CatchScope.begin(), 1129 NumHandlers * sizeof(EHCatchScope::Handler)); 1130 EHStack.popCatch(); 1131 1132 // The fall-through block. 1133 llvm::BasicBlock *ContBB = createBasicBlock("try.cont"); 1134 1135 // We just emitted the body of the try; jump to the continue block. 1136 if (HaveInsertPoint()) 1137 Builder.CreateBr(ContBB); 1138 1139 // Determine if we need an implicit rethrow for all these catch handlers. 1140 bool ImplicitRethrow = false; 1141 if (IsFnTryBlock) 1142 ImplicitRethrow = isa<CXXDestructorDecl>(CurCodeDecl) || 1143 isa<CXXConstructorDecl>(CurCodeDecl); 1144 1145 for (unsigned I = 0; I != NumHandlers; ++I) { 1146 llvm::BasicBlock *CatchBlock = Handlers[I].Block; 1147 EmitBlock(CatchBlock); 1148 1149 // Catch the exception if this isn't a catch-all. 1150 const CXXCatchStmt *C = S.getHandler(I); 1151 1152 // Enter a cleanup scope, including the catch variable and the 1153 // end-catch. 1154 RunCleanupsScope CatchScope(*this); 1155 1156 // Initialize the catch variable and set up the cleanups. 1157 BeginCatch(*this, C); 1158 1159 // If there's an implicit rethrow, push a normal "cleanup" to call 1160 // _cxa_rethrow. This needs to happen before __cxa_end_catch is 1161 // called, and so it is pushed after BeginCatch. 1162 if (ImplicitRethrow) 1163 EHStack.pushCleanup<CallRethrow>(NormalCleanup); 1164 1165 // Perform the body of the catch. 1166 EmitStmt(C->getHandlerBlock()); 1167 1168 // Fall out through the catch cleanups. 1169 CatchScope.ForceCleanup(); 1170 1171 // Branch out of the try. 1172 if (HaveInsertPoint()) 1173 Builder.CreateBr(ContBB); 1174 } 1175 1176 EmitBlock(ContBB); 1177} 1178 1179namespace { 1180 struct CallEndCatchForFinally : EHScopeStack::Cleanup { 1181 llvm::Value *ForEHVar; 1182 llvm::Value *EndCatchFn; 1183 CallEndCatchForFinally(llvm::Value *ForEHVar, llvm::Value *EndCatchFn) 1184 : ForEHVar(ForEHVar), EndCatchFn(EndCatchFn) {} 1185 1186 void Emit(CodeGenFunction &CGF, bool IsForEH) { 1187 llvm::BasicBlock *EndCatchBB = CGF.createBasicBlock("finally.endcatch"); 1188 llvm::BasicBlock *CleanupContBB = 1189 CGF.createBasicBlock("finally.cleanup.cont"); 1190 1191 llvm::Value *ShouldEndCatch = 1192 CGF.Builder.CreateLoad(ForEHVar, "finally.endcatch"); 1193 CGF.Builder.CreateCondBr(ShouldEndCatch, EndCatchBB, CleanupContBB); 1194 CGF.EmitBlock(EndCatchBB); 1195 CGF.EmitCallOrInvoke(EndCatchFn, 0, 0); // catch-all, so might throw 1196 CGF.EmitBlock(CleanupContBB); 1197 } 1198 }; 1199 1200 struct PerformFinally : EHScopeStack::Cleanup { 1201 const Stmt *Body; 1202 llvm::Value *ForEHVar; 1203 llvm::Value *EndCatchFn; 1204 llvm::Value *RethrowFn; 1205 llvm::Value *SavedExnVar; 1206 1207 PerformFinally(const Stmt *Body, llvm::Value *ForEHVar, 1208 llvm::Value *EndCatchFn, 1209 llvm::Value *RethrowFn, llvm::Value *SavedExnVar) 1210 : Body(Body), ForEHVar(ForEHVar), EndCatchFn(EndCatchFn), 1211 RethrowFn(RethrowFn), SavedExnVar(SavedExnVar) {} 1212 1213 void Emit(CodeGenFunction &CGF, bool IsForEH) { 1214 // Enter a cleanup to call the end-catch function if one was provided. 1215 if (EndCatchFn) 1216 CGF.EHStack.pushCleanup<CallEndCatchForFinally>(NormalAndEHCleanup, 1217 ForEHVar, EndCatchFn); 1218 1219 // Save the current cleanup destination in case there are 1220 // cleanups in the finally block. 1221 llvm::Value *SavedCleanupDest = 1222 CGF.Builder.CreateLoad(CGF.getNormalCleanupDestSlot(), 1223 "cleanup.dest.saved"); 1224 1225 // Emit the finally block. 1226 CGF.EmitStmt(Body); 1227 1228 // If the end of the finally is reachable, check whether this was 1229 // for EH. If so, rethrow. 1230 if (CGF.HaveInsertPoint()) { 1231 llvm::BasicBlock *RethrowBB = CGF.createBasicBlock("finally.rethrow"); 1232 llvm::BasicBlock *ContBB = CGF.createBasicBlock("finally.cont"); 1233 1234 llvm::Value *ShouldRethrow = 1235 CGF.Builder.CreateLoad(ForEHVar, "finally.shouldthrow"); 1236 CGF.Builder.CreateCondBr(ShouldRethrow, RethrowBB, ContBB); 1237 1238 CGF.EmitBlock(RethrowBB); 1239 if (SavedExnVar) { 1240 llvm::Value *Args[] = { CGF.Builder.CreateLoad(SavedExnVar) }; 1241 CGF.EmitCallOrInvoke(RethrowFn, Args, Args+1); 1242 } else { 1243 CGF.EmitCallOrInvoke(RethrowFn, 0, 0); 1244 } 1245 CGF.Builder.CreateUnreachable(); 1246 1247 CGF.EmitBlock(ContBB); 1248 1249 // Restore the cleanup destination. 1250 CGF.Builder.CreateStore(SavedCleanupDest, 1251 CGF.getNormalCleanupDestSlot()); 1252 } 1253 1254 // Leave the end-catch cleanup. As an optimization, pretend that 1255 // the fallthrough path was inaccessible; we've dynamically proven 1256 // that we're not in the EH case along that path. 1257 if (EndCatchFn) { 1258 CGBuilderTy::InsertPoint SavedIP = CGF.Builder.saveAndClearIP(); 1259 CGF.PopCleanupBlock(); 1260 CGF.Builder.restoreIP(SavedIP); 1261 } 1262 1263 // Now make sure we actually have an insertion point or the 1264 // cleanup gods will hate us. 1265 CGF.EnsureInsertPoint(); 1266 } 1267 }; 1268} 1269 1270/// Enters a finally block for an implementation using zero-cost 1271/// exceptions. This is mostly general, but hard-codes some 1272/// language/ABI-specific behavior in the catch-all sections. 1273CodeGenFunction::FinallyInfo 1274CodeGenFunction::EnterFinallyBlock(const Stmt *Body, 1275 llvm::Constant *BeginCatchFn, 1276 llvm::Constant *EndCatchFn, 1277 llvm::Constant *RethrowFn) { 1278 assert((BeginCatchFn != 0) == (EndCatchFn != 0) && 1279 "begin/end catch functions not paired"); 1280 assert(RethrowFn && "rethrow function is required"); 1281 1282 // The rethrow function has one of the following two types: 1283 // void (*)() 1284 // void (*)(void*) 1285 // In the latter case we need to pass it the exception object. 1286 // But we can't use the exception slot because the @finally might 1287 // have a landing pad (which would overwrite the exception slot). 1288 const llvm::FunctionType *RethrowFnTy = 1289 cast<llvm::FunctionType>( 1290 cast<llvm::PointerType>(RethrowFn->getType()) 1291 ->getElementType()); 1292 llvm::Value *SavedExnVar = 0; 1293 if (RethrowFnTy->getNumParams()) 1294 SavedExnVar = CreateTempAlloca(Builder.getInt8PtrTy(), "finally.exn"); 1295 1296 // A finally block is a statement which must be executed on any edge 1297 // out of a given scope. Unlike a cleanup, the finally block may 1298 // contain arbitrary control flow leading out of itself. In 1299 // addition, finally blocks should always be executed, even if there 1300 // are no catch handlers higher on the stack. Therefore, we 1301 // surround the protected scope with a combination of a normal 1302 // cleanup (to catch attempts to break out of the block via normal 1303 // control flow) and an EH catch-all (semantically "outside" any try 1304 // statement to which the finally block might have been attached). 1305 // The finally block itself is generated in the context of a cleanup 1306 // which conditionally leaves the catch-all. 1307 1308 FinallyInfo Info; 1309 1310 // Jump destination for performing the finally block on an exception 1311 // edge. We'll never actually reach this block, so unreachable is 1312 // fine. 1313 JumpDest RethrowDest = getJumpDestInCurrentScope(getUnreachableBlock()); 1314 1315 // Whether the finally block is being executed for EH purposes. 1316 llvm::AllocaInst *ForEHVar = CreateTempAlloca(Builder.getInt1Ty(), 1317 "finally.for-eh"); 1318 InitTempAlloca(ForEHVar, llvm::ConstantInt::getFalse(getLLVMContext())); 1319 1320 // Enter a normal cleanup which will perform the @finally block. 1321 EHStack.pushCleanup<PerformFinally>(NormalCleanup, Body, 1322 ForEHVar, EndCatchFn, 1323 RethrowFn, SavedExnVar); 1324 1325 // Enter a catch-all scope. 1326 llvm::BasicBlock *CatchAllBB = createBasicBlock("finally.catchall"); 1327 CGBuilderTy::InsertPoint SavedIP = Builder.saveIP(); 1328 Builder.SetInsertPoint(CatchAllBB); 1329 1330 // If there's a begin-catch function, call it. 1331 if (BeginCatchFn) { 1332 Builder.CreateCall(BeginCatchFn, Builder.CreateLoad(getExceptionSlot())) 1333 ->setDoesNotThrow(); 1334 } 1335 1336 // If we need to remember the exception pointer to rethrow later, do so. 1337 if (SavedExnVar) { 1338 llvm::Value *SavedExn = Builder.CreateLoad(getExceptionSlot()); 1339 Builder.CreateStore(SavedExn, SavedExnVar); 1340 } 1341 1342 // Tell the finally block that we're in EH. 1343 Builder.CreateStore(llvm::ConstantInt::getTrue(getLLVMContext()), ForEHVar); 1344 1345 // Thread a jump through the finally cleanup. 1346 EmitBranchThroughCleanup(RethrowDest); 1347 1348 Builder.restoreIP(SavedIP); 1349 1350 EHCatchScope *CatchScope = EHStack.pushCatch(1); 1351 CatchScope->setCatchAllHandler(0, CatchAllBB); 1352 1353 return Info; 1354} 1355 1356void CodeGenFunction::ExitFinallyBlock(FinallyInfo &Info) { 1357 // Leave the finally catch-all. 1358 EHCatchScope &Catch = cast<EHCatchScope>(*EHStack.begin()); 1359 llvm::BasicBlock *CatchAllBB = Catch.getHandler(0).Block; 1360 EHStack.popCatch(); 1361 1362 // And leave the normal cleanup. 1363 PopCleanupBlock(); 1364 1365 CGBuilderTy::InsertPoint SavedIP = Builder.saveAndClearIP(); 1366 EmitBlock(CatchAllBB, true); 1367 1368 Builder.restoreIP(SavedIP); 1369} 1370 1371llvm::BasicBlock *CodeGenFunction::getTerminateLandingPad() { 1372 if (TerminateLandingPad) 1373 return TerminateLandingPad; 1374 1375 CGBuilderTy::InsertPoint SavedIP = Builder.saveAndClearIP(); 1376 1377 // This will get inserted at the end of the function. 1378 TerminateLandingPad = createBasicBlock("terminate.lpad"); 1379 Builder.SetInsertPoint(TerminateLandingPad); 1380 1381 // Tell the backend that this is a landing pad. 1382 llvm::CallInst *Exn = 1383 Builder.CreateCall(CGM.getIntrinsic(llvm::Intrinsic::eh_exception), "exn"); 1384 Exn->setDoesNotThrow(); 1385 1386 const EHPersonality &Personality = EHPersonality::get(CGM.getLangOptions()); 1387 1388 // Tell the backend what the exception table should be: 1389 // nothing but a catch-all. 1390 llvm::Value *Args[3] = { Exn, getOpaquePersonalityFn(CGM, Personality), 1391 getCatchAllValue(*this) }; 1392 Builder.CreateCall(CGM.getIntrinsic(llvm::Intrinsic::eh_selector), 1393 Args, Args+3, "eh.selector") 1394 ->setDoesNotThrow(); 1395 1396 llvm::CallInst *TerminateCall = Builder.CreateCall(getTerminateFn(*this)); 1397 TerminateCall->setDoesNotReturn(); 1398 TerminateCall->setDoesNotThrow(); 1399 Builder.CreateUnreachable(); 1400 1401 // Restore the saved insertion state. 1402 Builder.restoreIP(SavedIP); 1403 1404 return TerminateLandingPad; 1405} 1406 1407llvm::BasicBlock *CodeGenFunction::getTerminateHandler() { 1408 if (TerminateHandler) 1409 return TerminateHandler; 1410 1411 CGBuilderTy::InsertPoint SavedIP = Builder.saveAndClearIP(); 1412 1413 // Set up the terminate handler. This block is inserted at the very 1414 // end of the function by FinishFunction. 1415 TerminateHandler = createBasicBlock("terminate.handler"); 1416 Builder.SetInsertPoint(TerminateHandler); 1417 llvm::CallInst *TerminateCall = Builder.CreateCall(getTerminateFn(*this)); 1418 TerminateCall->setDoesNotReturn(); 1419 TerminateCall->setDoesNotThrow(); 1420 Builder.CreateUnreachable(); 1421 1422 // Restore the saved insertion state. 1423 Builder.restoreIP(SavedIP); 1424 1425 return TerminateHandler; 1426} 1427 1428CodeGenFunction::UnwindDest CodeGenFunction::getRethrowDest() { 1429 if (RethrowBlock.isValid()) return RethrowBlock; 1430 1431 CGBuilderTy::InsertPoint SavedIP = Builder.saveIP(); 1432 1433 // We emit a jump to a notional label at the outermost unwind state. 1434 llvm::BasicBlock *Unwind = createBasicBlock("eh.resume"); 1435 Builder.SetInsertPoint(Unwind); 1436 1437 const EHPersonality &Personality = EHPersonality::get(CGM.getLangOptions()); 1438 1439 // This can always be a call because we necessarily didn't find 1440 // anything on the EH stack which needs our help. 1441 llvm::StringRef RethrowName = Personality.getCatchallRethrowFnName(); 1442 llvm::Constant *RethrowFn; 1443 if (!RethrowName.empty()) 1444 RethrowFn = getCatchallRethrowFn(*this, RethrowName); 1445 else 1446 RethrowFn = getUnwindResumeOrRethrowFn(); 1447 1448 Builder.CreateCall(RethrowFn, Builder.CreateLoad(getExceptionSlot())) 1449 ->setDoesNotReturn(); 1450 Builder.CreateUnreachable(); 1451 1452 Builder.restoreIP(SavedIP); 1453 1454 RethrowBlock = UnwindDest(Unwind, EHStack.stable_end(), 0); 1455 return RethrowBlock; 1456} 1457 1458