1 //===-- EHScopeStack.h - Stack for cleanup IR generation --------*- C++ -*-===// 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 // These classes should be the minimum interface required for other parts of 10 // CodeGen to emit cleanups. The implementation is in CGCleanup.cpp and other 11 // implemenentation details that are not widely needed are in CGCleanup.h. 12 // 13 //===----------------------------------------------------------------------===// 14 15 #ifndef LLVM_CLANG_LIB_CODEGEN_EHSCOPESTACK_H 16 #define LLVM_CLANG_LIB_CODEGEN_EHSCOPESTACK_H 17 18 #include "clang/Basic/LLVM.h" 19 #include "llvm/ADT/STLExtras.h" 20 #include "llvm/ADT/SmallVector.h" 21 #include "llvm/IR/BasicBlock.h" 22 #include "llvm/IR/Instructions.h" 23 #include "llvm/IR/Value.h" 24 25 namespace clang { 26 namespace CodeGen { 27 28 class CodeGenFunction; 29 30 /// A branch fixup. These are required when emitting a goto to a 31 /// label which hasn't been emitted yet. The goto is optimistically 32 /// emitted as a branch to the basic block for the label, and (if it 33 /// occurs in a scope with non-trivial cleanups) a fixup is added to 34 /// the innermost cleanup. When a (normal) cleanup is popped, any 35 /// unresolved fixups in that scope are threaded through the cleanup. 36 struct BranchFixup { 37 /// The block containing the terminator which needs to be modified 38 /// into a switch if this fixup is resolved into the current scope. 39 /// If null, LatestBranch points directly to the destination. 40 llvm::BasicBlock *OptimisticBranchBlock; 41 42 /// The ultimate destination of the branch. 43 /// 44 /// This can be set to null to indicate that this fixup was 45 /// successfully resolved. 46 llvm::BasicBlock *Destination; 47 48 /// The destination index value. 49 unsigned DestinationIndex; 50 51 /// The initial branch of the fixup. 52 llvm::BranchInst *InitialBranch; 53 }; 54 55 template <class T> struct InvariantValue { 56 typedef T type; 57 typedef T saved_type; 58 static bool needsSaving(type value) { return false; } 59 static saved_type save(CodeGenFunction &CGF, type value) { return value; } 60 static type restore(CodeGenFunction &CGF, saved_type value) { return value; } 61 }; 62 63 /// A metaprogramming class for ensuring that a value will dominate an 64 /// arbitrary position in a function. 65 template <class T> struct DominatingValue : InvariantValue<T> {}; 66 67 template <class T, bool mightBeInstruction = 68 std::is_base_of<llvm::Value, T>::value && 69 !std::is_base_of<llvm::Constant, T>::value && 70 !std::is_base_of<llvm::BasicBlock, T>::value> 71 struct DominatingPointer; 72 template <class T> struct DominatingPointer<T,false> : InvariantValue<T*> {}; 73 // template <class T> struct DominatingPointer<T,true> at end of file 74 75 template <class T> struct DominatingValue<T*> : DominatingPointer<T> {}; 76 77 enum CleanupKind : unsigned { 78 /// Denotes a cleanup that should run when a scope is exited using exceptional 79 /// control flow (a throw statement leading to stack unwinding, ). 80 EHCleanup = 0x1, 81 82 /// Denotes a cleanup that should run when a scope is exited using normal 83 /// control flow (falling off the end of the scope, return, goto, ...). 84 NormalCleanup = 0x2, 85 86 NormalAndEHCleanup = EHCleanup | NormalCleanup, 87 88 LifetimeMarker = 0x8, 89 NormalEHLifetimeMarker = LifetimeMarker | NormalAndEHCleanup, 90 }; 91 92 /// A stack of scopes which respond to exceptions, including cleanups 93 /// and catch blocks. 94 class EHScopeStack { 95 public: 96 /* Should switch to alignof(uint64_t) instead of 8, when EHCleanupScope can */ 97 enum { ScopeStackAlignment = 8 }; 98 99 /// A saved depth on the scope stack. This is necessary because 100 /// pushing scopes onto the stack invalidates iterators. 101 class stable_iterator { 102 friend class EHScopeStack; 103 104 /// Offset from StartOfData to EndOfBuffer. 105 ptrdiff_t Size; 106 107 stable_iterator(ptrdiff_t Size) : Size(Size) {} 108 109 public: 110 static stable_iterator invalid() { return stable_iterator(-1); } 111 stable_iterator() : Size(-1) {} 112 113 bool isValid() const { return Size >= 0; } 114 115 /// Returns true if this scope encloses I. 116 /// Returns false if I is invalid. 117 /// This scope must be valid. 118 bool encloses(stable_iterator I) const { return Size <= I.Size; } 119 120 /// Returns true if this scope strictly encloses I: that is, 121 /// if it encloses I and is not I. 122 /// Returns false is I is invalid. 123 /// This scope must be valid. 124 bool strictlyEncloses(stable_iterator I) const { return Size < I.Size; } 125 126 friend bool operator==(stable_iterator A, stable_iterator B) { 127 return A.Size == B.Size; 128 } 129 friend bool operator!=(stable_iterator A, stable_iterator B) { 130 return A.Size != B.Size; 131 } 132 }; 133 134 /// Information for lazily generating a cleanup. Subclasses must be 135 /// POD-like: cleanups will not be destructed, and they will be 136 /// allocated on the cleanup stack and freely copied and moved 137 /// around. 138 /// 139 /// Cleanup implementations should generally be declared in an 140 /// anonymous namespace. 141 class Cleanup { 142 // Anchor the construction vtable. 143 virtual void anchor(); 144 145 protected: 146 ~Cleanup() = default; 147 148 public: 149 Cleanup(const Cleanup &) = default; 150 Cleanup(Cleanup &&) {} 151 152 // The copy and move assignment operator is defined as deleted pending 153 // further motivation. 154 Cleanup &operator=(const Cleanup &) = delete; 155 Cleanup &operator=(Cleanup &&) = delete; 156 157 Cleanup() = default; 158 159 virtual bool isRedundantBeforeReturn() { return false; } 160 161 /// Generation flags. 162 class Flags { 163 enum { 164 F_IsForEH = 0x1, 165 F_IsNormalCleanupKind = 0x2, 166 F_IsEHCleanupKind = 0x4, 167 F_HasExitSwitch = 0x8, 168 }; 169 unsigned flags; 170 171 public: 172 Flags() : flags(0) {} 173 174 /// isForEH - true if the current emission is for an EH cleanup. 175 bool isForEHCleanup() const { return flags & F_IsForEH; } 176 bool isForNormalCleanup() const { return !isForEHCleanup(); } 177 void setIsForEHCleanup() { flags |= F_IsForEH; } 178 179 bool isNormalCleanupKind() const { return flags & F_IsNormalCleanupKind; } 180 void setIsNormalCleanupKind() { flags |= F_IsNormalCleanupKind; } 181 182 /// isEHCleanupKind - true if the cleanup was pushed as an EH 183 /// cleanup. 184 bool isEHCleanupKind() const { return flags & F_IsEHCleanupKind; } 185 void setIsEHCleanupKind() { flags |= F_IsEHCleanupKind; } 186 187 bool hasExitSwitch() const { return flags & F_HasExitSwitch; } 188 void setHasExitSwitch() { flags |= F_HasExitSwitch; } 189 }; 190 191 /// Emit the cleanup. For normal cleanups, this is run in the 192 /// same EH context as when the cleanup was pushed, i.e. the 193 /// immediately-enclosing context of the cleanup scope. For 194 /// EH cleanups, this is run in a terminate context. 195 /// 196 // \param flags cleanup kind. 197 virtual void Emit(CodeGenFunction &CGF, Flags flags) = 0; 198 }; 199 200 /// ConditionalCleanup stores the saved form of its parameters, 201 /// then restores them and performs the cleanup. 202 template <class T, class... As> 203 class ConditionalCleanup final : public Cleanup { 204 typedef std::tuple<typename DominatingValue<As>::saved_type...> SavedTuple; 205 SavedTuple Saved; 206 207 template <std::size_t... Is> 208 T restore(CodeGenFunction &CGF, std::index_sequence<Is...>) { 209 // It's important that the restores are emitted in order. The braced init 210 // list guarantees that. 211 return T{DominatingValue<As>::restore(CGF, std::get<Is>(Saved))...}; 212 } 213 214 void Emit(CodeGenFunction &CGF, Flags flags) override { 215 restore(CGF, std::index_sequence_for<As...>()).Emit(CGF, flags); 216 } 217 218 public: 219 ConditionalCleanup(typename DominatingValue<As>::saved_type... A) 220 : Saved(A...) {} 221 222 ConditionalCleanup(SavedTuple Tuple) : Saved(std::move(Tuple)) {} 223 }; 224 225 private: 226 // The implementation for this class is in CGException.h and 227 // CGException.cpp; the definition is here because it's used as a 228 // member of CodeGenFunction. 229 230 /// The start of the scope-stack buffer, i.e. the allocated pointer 231 /// for the buffer. All of these pointers are either simultaneously 232 /// null or simultaneously valid. 233 char *StartOfBuffer; 234 235 /// The end of the buffer. 236 char *EndOfBuffer; 237 238 /// The first valid entry in the buffer. 239 char *StartOfData; 240 241 /// The innermost normal cleanup on the stack. 242 stable_iterator InnermostNormalCleanup; 243 244 /// The innermost EH scope on the stack. 245 stable_iterator InnermostEHScope; 246 247 /// The CGF this Stack belong to 248 CodeGenFunction* CGF; 249 250 /// The current set of branch fixups. A branch fixup is a jump to 251 /// an as-yet unemitted label, i.e. a label for which we don't yet 252 /// know the EH stack depth. Whenever we pop a cleanup, we have 253 /// to thread all the current branch fixups through it. 254 /// 255 /// Fixups are recorded as the Use of the respective branch or 256 /// switch statement. The use points to the final destination. 257 /// When popping out of a cleanup, these uses are threaded through 258 /// the cleanup and adjusted to point to the new cleanup. 259 /// 260 /// Note that branches are allowed to jump into protected scopes 261 /// in certain situations; e.g. the following code is legal: 262 /// struct A { ~A(); }; // trivial ctor, non-trivial dtor 263 /// goto foo; 264 /// A a; 265 /// foo: 266 /// bar(); 267 SmallVector<BranchFixup, 8> BranchFixups; 268 269 char *allocate(size_t Size); 270 void deallocate(size_t Size); 271 272 void *pushCleanup(CleanupKind K, size_t DataSize); 273 274 public: 275 EHScopeStack() 276 : StartOfBuffer(nullptr), EndOfBuffer(nullptr), StartOfData(nullptr), 277 InnermostNormalCleanup(stable_end()), InnermostEHScope(stable_end()), 278 CGF(nullptr) {} 279 ~EHScopeStack() { delete[] StartOfBuffer; } 280 281 EHScopeStack(const EHScopeStack &) = delete; 282 EHScopeStack &operator=(const EHScopeStack &) = delete; 283 284 /// Push a lazily-created cleanup on the stack. 285 template <class T, class... As> void pushCleanup(CleanupKind Kind, As... A) { 286 static_assert(alignof(T) <= ScopeStackAlignment, 287 "Cleanup's alignment is too large."); 288 void *Buffer = pushCleanup(Kind, sizeof(T)); 289 Cleanup *Obj = new (Buffer) T(A...); 290 (void) Obj; 291 } 292 293 /// Push a lazily-created cleanup on the stack. Tuple version. 294 template <class T, class... As> 295 void pushCleanupTuple(CleanupKind Kind, std::tuple<As...> A) { 296 static_assert(alignof(T) <= ScopeStackAlignment, 297 "Cleanup's alignment is too large."); 298 void *Buffer = pushCleanup(Kind, sizeof(T)); 299 Cleanup *Obj = new (Buffer) T(std::move(A)); 300 (void) Obj; 301 } 302 303 // Feel free to add more variants of the following: 304 305 /// Push a cleanup with non-constant storage requirements on the 306 /// stack. The cleanup type must provide an additional static method: 307 /// static size_t getExtraSize(size_t); 308 /// The argument to this method will be the value N, which will also 309 /// be passed as the first argument to the constructor. 310 /// 311 /// The data stored in the extra storage must obey the same 312 /// restrictions as normal cleanup member data. 313 /// 314 /// The pointer returned from this method is valid until the cleanup 315 /// stack is modified. 316 template <class T, class... As> 317 T *pushCleanupWithExtra(CleanupKind Kind, size_t N, As... A) { 318 static_assert(alignof(T) <= ScopeStackAlignment, 319 "Cleanup's alignment is too large."); 320 void *Buffer = pushCleanup(Kind, sizeof(T) + T::getExtraSize(N)); 321 return new (Buffer) T(N, A...); 322 } 323 324 void pushCopyOfCleanup(CleanupKind Kind, const void *Cleanup, size_t Size) { 325 void *Buffer = pushCleanup(Kind, Size); 326 std::memcpy(Buffer, Cleanup, Size); 327 } 328 329 void setCGF(CodeGenFunction *inCGF) { CGF = inCGF; } 330 331 /// Pops a cleanup scope off the stack. This is private to CGCleanup.cpp. 332 void popCleanup(); 333 334 /// Push a set of catch handlers on the stack. The catch is 335 /// uninitialized and will need to have the given number of handlers 336 /// set on it. 337 class EHCatchScope *pushCatch(unsigned NumHandlers); 338 339 /// Pops a catch scope off the stack. This is private to CGException.cpp. 340 void popCatch(); 341 342 /// Push an exceptions filter on the stack. 343 class EHFilterScope *pushFilter(unsigned NumFilters); 344 345 /// Pops an exceptions filter off the stack. 346 void popFilter(); 347 348 /// Push a terminate handler on the stack. 349 void pushTerminate(); 350 351 /// Pops a terminate handler off the stack. 352 void popTerminate(); 353 354 // Returns true iff the current scope is either empty or contains only 355 // lifetime markers, i.e. no real cleanup code 356 bool containsOnlyLifetimeMarkers(stable_iterator Old) const; 357 358 /// Determines whether the exception-scopes stack is empty. 359 bool empty() const { return StartOfData == EndOfBuffer; } 360 361 bool requiresLandingPad() const; 362 363 /// Determines whether there are any normal cleanups on the stack. 364 bool hasNormalCleanups() const { 365 return InnermostNormalCleanup != stable_end(); 366 } 367 368 /// Returns the innermost normal cleanup on the stack, or 369 /// stable_end() if there are no normal cleanups. 370 stable_iterator getInnermostNormalCleanup() const { 371 return InnermostNormalCleanup; 372 } 373 stable_iterator getInnermostActiveNormalCleanup() const; 374 375 stable_iterator getInnermostEHScope() const { 376 return InnermostEHScope; 377 } 378 379 380 /// An unstable reference to a scope-stack depth. Invalidated by 381 /// pushes but not pops. 382 class iterator; 383 384 /// Returns an iterator pointing to the innermost EH scope. 385 iterator begin() const; 386 387 /// Returns an iterator pointing to the outermost EH scope. 388 iterator end() const; 389 390 /// Create a stable reference to the top of the EH stack. The 391 /// returned reference is valid until that scope is popped off the 392 /// stack. 393 stable_iterator stable_begin() const { 394 return stable_iterator(EndOfBuffer - StartOfData); 395 } 396 397 /// Create a stable reference to the bottom of the EH stack. 398 static stable_iterator stable_end() { 399 return stable_iterator(0); 400 } 401 402 /// Translates an iterator into a stable_iterator. 403 stable_iterator stabilize(iterator it) const; 404 405 /// Turn a stable reference to a scope depth into a unstable pointer 406 /// to the EH stack. 407 iterator find(stable_iterator save) const; 408 409 /// Add a branch fixup to the current cleanup scope. 410 BranchFixup &addBranchFixup() { 411 assert(hasNormalCleanups() && "adding fixup in scope without cleanups"); 412 BranchFixups.push_back(BranchFixup()); 413 return BranchFixups.back(); 414 } 415 416 unsigned getNumBranchFixups() const { return BranchFixups.size(); } 417 BranchFixup &getBranchFixup(unsigned I) { 418 assert(I < getNumBranchFixups()); 419 return BranchFixups[I]; 420 } 421 422 /// Pops lazily-removed fixups from the end of the list. This 423 /// should only be called by procedures which have just popped a 424 /// cleanup or resolved one or more fixups. 425 void popNullFixups(); 426 427 /// Clears the branch-fixups list. This should only be called by 428 /// ResolveAllBranchFixups. 429 void clearFixups() { BranchFixups.clear(); } 430 }; 431 432 } // namespace CodeGen 433 } // namespace clang 434 435 #endif 436