1 //===-- EHScopeStack.h - Stack for cleanup IR generation --------*- C++ -*-===// 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 // These classes should be the minimum interface required for other parts of 11 // CodeGen to emit cleanups. The implementation is in CGCleanup.cpp and other 12 // implemenentation details that are not widely needed are in CGCleanup.h. 13 // 14 //===----------------------------------------------------------------------===// 15 16 #ifndef LLVM_CLANG_LIB_CODEGEN_EHSCOPESTACK_H 17 #define LLVM_CLANG_LIB_CODEGEN_EHSCOPESTACK_H 18 19 #include "clang/Basic/LLVM.h" 20 #include "llvm/ADT/STLExtras.h" 21 #include "llvm/ADT/SmallVector.h" 22 #include "llvm/IR/BasicBlock.h" 23 #include "llvm/IR/Instructions.h" 24 #include "llvm/IR/Value.h" 25 26 namespace clang { 27 namespace CodeGen { 28 29 class CodeGenFunction; 30 31 /// A branch fixup. These are required when emitting a goto to a 32 /// label which hasn't been emitted yet. The goto is optimistically 33 /// emitted as a branch to the basic block for the label, and (if it 34 /// occurs in a scope with non-trivial cleanups) a fixup is added to 35 /// the innermost cleanup. When a (normal) cleanup is popped, any 36 /// unresolved fixups in that scope are threaded through the cleanup. 37 struct BranchFixup { 38 /// The block containing the terminator which needs to be modified 39 /// into a switch if this fixup is resolved into the current scope. 40 /// If null, LatestBranch points directly to the destination. 41 llvm::BasicBlock *OptimisticBranchBlock; 42 43 /// The ultimate destination of the branch. 44 /// 45 /// This can be set to null to indicate that this fixup was 46 /// successfully resolved. 47 llvm::BasicBlock *Destination; 48 49 /// The destination index value. 50 unsigned DestinationIndex; 51 52 /// The initial branch of the fixup. 53 llvm::BranchInst *InitialBranch; 54 }; 55 56 template <class T> struct InvariantValue { 57 typedef T type; 58 typedef T saved_type; needsSavingInvariantValue59 static bool needsSaving(type value) { return false; } saveInvariantValue60 static saved_type save(CodeGenFunction &CGF, type value) { return value; } restoreInvariantValue61 static type restore(CodeGenFunction &CGF, saved_type value) { return value; } 62 }; 63 64 /// A metaprogramming class for ensuring that a value will dominate an 65 /// arbitrary position in a function. 66 template <class T> struct DominatingValue : InvariantValue<T> {}; 67 68 template <class T, bool mightBeInstruction = 69 std::is_base_of<llvm::Value, T>::value && 70 !std::is_base_of<llvm::Constant, T>::value && 71 !std::is_base_of<llvm::BasicBlock, T>::value> 72 struct DominatingPointer; 73 template <class T> struct DominatingPointer<T,false> : InvariantValue<T*> {}; 74 // template <class T> struct DominatingPointer<T,true> at end of file 75 76 template <class T> struct DominatingValue<T*> : DominatingPointer<T> {}; 77 78 enum CleanupKind : unsigned { 79 /// Denotes a cleanup that should run when a scope is exited using exceptional 80 /// control flow (a throw statement leading to stack unwinding, ). 81 EHCleanup = 0x1, 82 83 /// Denotes a cleanup that should run when a scope is exited using normal 84 /// control flow (falling off the end of the scope, return, goto, ...). 85 NormalCleanup = 0x2, 86 87 NormalAndEHCleanup = EHCleanup | NormalCleanup, 88 89 InactiveCleanup = 0x4, 90 InactiveEHCleanup = EHCleanup | InactiveCleanup, 91 InactiveNormalCleanup = NormalCleanup | InactiveCleanup, 92 InactiveNormalAndEHCleanup = NormalAndEHCleanup | InactiveCleanup, 93 94 LifetimeMarker = 0x8, 95 NormalEHLifetimeMarker = LifetimeMarker | NormalAndEHCleanup, 96 }; 97 98 /// A stack of scopes which respond to exceptions, including cleanups 99 /// and catch blocks. 100 class EHScopeStack { 101 public: 102 /* Should switch to alignof(uint64_t) instead of 8, when EHCleanupScope can */ 103 enum { ScopeStackAlignment = 8 }; 104 105 /// A saved depth on the scope stack. This is necessary because 106 /// pushing scopes onto the stack invalidates iterators. 107 class stable_iterator { 108 friend class EHScopeStack; 109 110 /// Offset from StartOfData to EndOfBuffer. 111 ptrdiff_t Size; 112 113 stable_iterator(ptrdiff_t Size) : Size(Size) {} 114 115 public: 116 static stable_iterator invalid() { return stable_iterator(-1); } 117 stable_iterator() : Size(-1) {} 118 119 bool isValid() const { return Size >= 0; } 120 121 /// Returns true if this scope encloses I. 122 /// Returns false if I is invalid. 123 /// This scope must be valid. 124 bool encloses(stable_iterator I) const { return Size <= I.Size; } 125 126 /// Returns true if this scope strictly encloses I: that is, 127 /// if it encloses I and is not I. 128 /// Returns false is I is invalid. 129 /// This scope must be valid. 130 bool strictlyEncloses(stable_iterator I) const { return Size < I.Size; } 131 132 friend bool operator==(stable_iterator A, stable_iterator B) { 133 return A.Size == B.Size; 134 } 135 friend bool operator!=(stable_iterator A, stable_iterator B) { 136 return A.Size != B.Size; 137 } 138 }; 139 140 /// Information for lazily generating a cleanup. Subclasses must be 141 /// POD-like: cleanups will not be destructed, and they will be 142 /// allocated on the cleanup stack and freely copied and moved 143 /// around. 144 /// 145 /// Cleanup implementations should generally be declared in an 146 /// anonymous namespace. 147 class Cleanup { 148 // Anchor the construction vtable. 149 virtual void anchor(); 150 151 protected: 152 ~Cleanup() = default; 153 154 public: 155 Cleanup(const Cleanup &) = default; 156 Cleanup(Cleanup &&) {} 157 Cleanup() = default; 158 159 /// Generation flags. 160 class Flags { 161 enum { 162 F_IsForEH = 0x1, 163 F_IsNormalCleanupKind = 0x2, 164 F_IsEHCleanupKind = 0x4 165 }; 166 unsigned flags; 167 168 public: 169 Flags() : flags(0) {} 170 171 /// isForEH - true if the current emission is for an EH cleanup. 172 bool isForEHCleanup() const { return flags & F_IsForEH; } 173 bool isForNormalCleanup() const { return !isForEHCleanup(); } 174 void setIsForEHCleanup() { flags |= F_IsForEH; } 175 176 bool isNormalCleanupKind() const { return flags & F_IsNormalCleanupKind; } 177 void setIsNormalCleanupKind() { flags |= F_IsNormalCleanupKind; } 178 179 /// isEHCleanupKind - true if the cleanup was pushed as an EH 180 /// cleanup. 181 bool isEHCleanupKind() const { return flags & F_IsEHCleanupKind; } 182 void setIsEHCleanupKind() { flags |= F_IsEHCleanupKind; } 183 }; 184 185 186 /// Emit the cleanup. For normal cleanups, this is run in the 187 /// same EH context as when the cleanup was pushed, i.e. the 188 /// immediately-enclosing context of the cleanup scope. For 189 /// EH cleanups, this is run in a terminate context. 190 /// 191 // \param flags cleanup kind. 192 virtual void Emit(CodeGenFunction &CGF, Flags flags) = 0; 193 }; 194 195 /// ConditionalCleanup stores the saved form of its parameters, 196 /// then restores them and performs the cleanup. 197 template <class T, class... As> 198 class ConditionalCleanup final : public Cleanup { 199 typedef std::tuple<typename DominatingValue<As>::saved_type...> SavedTuple; 200 SavedTuple Saved; 201 202 template <std::size_t... Is> 203 T restore(CodeGenFunction &CGF, llvm::index_sequence<Is...>) { 204 // It's important that the restores are emitted in order. The braced init 205 // list guarentees that. 206 return T{DominatingValue<As>::restore(CGF, std::get<Is>(Saved))...}; 207 } 208 209 void Emit(CodeGenFunction &CGF, Flags flags) override { 210 restore(CGF, llvm::index_sequence_for<As...>()).Emit(CGF, flags); 211 } 212 213 public: 214 ConditionalCleanup(typename DominatingValue<As>::saved_type... A) 215 : Saved(A...) {} 216 217 ConditionalCleanup(SavedTuple Tuple) : Saved(std::move(Tuple)) {} 218 }; 219 220 private: 221 // The implementation for this class is in CGException.h and 222 // CGException.cpp; the definition is here because it's used as a 223 // member of CodeGenFunction. 224 225 /// The start of the scope-stack buffer, i.e. the allocated pointer 226 /// for the buffer. All of these pointers are either simultaneously 227 /// null or simultaneously valid. 228 char *StartOfBuffer; 229 230 /// The end of the buffer. 231 char *EndOfBuffer; 232 233 /// The first valid entry in the buffer. 234 char *StartOfData; 235 236 /// The innermost normal cleanup on the stack. 237 stable_iterator InnermostNormalCleanup; 238 239 /// The innermost EH scope on the stack. 240 stable_iterator InnermostEHScope; 241 242 /// The current set of branch fixups. A branch fixup is a jump to 243 /// an as-yet unemitted label, i.e. a label for which we don't yet 244 /// know the EH stack depth. Whenever we pop a cleanup, we have 245 /// to thread all the current branch fixups through it. 246 /// 247 /// Fixups are recorded as the Use of the respective branch or 248 /// switch statement. The use points to the final destination. 249 /// When popping out of a cleanup, these uses are threaded through 250 /// the cleanup and adjusted to point to the new cleanup. 251 /// 252 /// Note that branches are allowed to jump into protected scopes 253 /// in certain situations; e.g. the following code is legal: 254 /// struct A { ~A(); }; // trivial ctor, non-trivial dtor 255 /// goto foo; 256 /// A a; 257 /// foo: 258 /// bar(); 259 SmallVector<BranchFixup, 8> BranchFixups; 260 261 char *allocate(size_t Size); 262 void deallocate(size_t Size); 263 264 void *pushCleanup(CleanupKind K, size_t DataSize); 265 266 public: 267 EHScopeStack() : StartOfBuffer(nullptr), EndOfBuffer(nullptr), 268 StartOfData(nullptr), InnermostNormalCleanup(stable_end()), 269 InnermostEHScope(stable_end()) {} 270 ~EHScopeStack() { delete[] StartOfBuffer; } 271 272 /// Push a lazily-created cleanup on the stack. 273 template <class T, class... As> void pushCleanup(CleanupKind Kind, As... A) { 274 static_assert(llvm::AlignOf<T>::Alignment <= ScopeStackAlignment, 275 "Cleanup's alignment is too large."); 276 void *Buffer = pushCleanup(Kind, sizeof(T)); 277 Cleanup *Obj = new (Buffer) T(A...); 278 (void) Obj; 279 } 280 281 /// Push a lazily-created cleanup on the stack. Tuple version. 282 template <class T, class... As> 283 void pushCleanupTuple(CleanupKind Kind, std::tuple<As...> A) { 284 static_assert(llvm::AlignOf<T>::Alignment <= ScopeStackAlignment, 285 "Cleanup's alignment is too large."); 286 void *Buffer = pushCleanup(Kind, sizeof(T)); 287 Cleanup *Obj = new (Buffer) T(std::move(A)); 288 (void) Obj; 289 } 290 291 // Feel free to add more variants of the following: 292 293 /// Push a cleanup with non-constant storage requirements on the 294 /// stack. The cleanup type must provide an additional static method: 295 /// static size_t getExtraSize(size_t); 296 /// The argument to this method will be the value N, which will also 297 /// be passed as the first argument to the constructor. 298 /// 299 /// The data stored in the extra storage must obey the same 300 /// restrictions as normal cleanup member data. 301 /// 302 /// The pointer returned from this method is valid until the cleanup 303 /// stack is modified. 304 template <class T, class... As> 305 T *pushCleanupWithExtra(CleanupKind Kind, size_t N, As... A) { 306 static_assert(llvm::AlignOf<T>::Alignment <= ScopeStackAlignment, 307 "Cleanup's alignment is too large."); 308 void *Buffer = pushCleanup(Kind, sizeof(T) + T::getExtraSize(N)); 309 return new (Buffer) T(N, A...); 310 } 311 312 void pushCopyOfCleanup(CleanupKind Kind, const void *Cleanup, size_t Size) { 313 void *Buffer = pushCleanup(Kind, Size); 314 std::memcpy(Buffer, Cleanup, Size); 315 } 316 317 /// Pops a cleanup scope off the stack. This is private to CGCleanup.cpp. 318 void popCleanup(); 319 320 /// Push a set of catch handlers on the stack. The catch is 321 /// uninitialized and will need to have the given number of handlers 322 /// set on it. 323 class EHCatchScope *pushCatch(unsigned NumHandlers); 324 325 /// Pops a catch scope off the stack. This is private to CGException.cpp. 326 void popCatch(); 327 328 /// Push an exceptions filter on the stack. 329 class EHFilterScope *pushFilter(unsigned NumFilters); 330 331 /// Pops an exceptions filter off the stack. 332 void popFilter(); 333 334 /// Push a terminate handler on the stack. 335 void pushTerminate(); 336 337 /// Pops a terminate handler off the stack. 338 void popTerminate(); 339 340 // Returns true iff the current scope is either empty or contains only 341 // lifetime markers, i.e. no real cleanup code 342 bool containsOnlyLifetimeMarkers(stable_iterator Old) const; 343 344 /// Determines whether the exception-scopes stack is empty. 345 bool empty() const { return StartOfData == EndOfBuffer; } 346 347 bool requiresLandingPad() const; 348 349 /// Determines whether there are any normal cleanups on the stack. 350 bool hasNormalCleanups() const { 351 return InnermostNormalCleanup != stable_end(); 352 } 353 354 /// Returns the innermost normal cleanup on the stack, or 355 /// stable_end() if there are no normal cleanups. 356 stable_iterator getInnermostNormalCleanup() const { 357 return InnermostNormalCleanup; 358 } 359 stable_iterator getInnermostActiveNormalCleanup() const; 360 361 stable_iterator getInnermostEHScope() const { 362 return InnermostEHScope; 363 } 364 365 366 /// An unstable reference to a scope-stack depth. Invalidated by 367 /// pushes but not pops. 368 class iterator; 369 370 /// Returns an iterator pointing to the innermost EH scope. 371 iterator begin() const; 372 373 /// Returns an iterator pointing to the outermost EH scope. 374 iterator end() const; 375 376 /// Create a stable reference to the top of the EH stack. The 377 /// returned reference is valid until that scope is popped off the 378 /// stack. 379 stable_iterator stable_begin() const { 380 return stable_iterator(EndOfBuffer - StartOfData); 381 } 382 383 /// Create a stable reference to the bottom of the EH stack. 384 static stable_iterator stable_end() { 385 return stable_iterator(0); 386 } 387 388 /// Translates an iterator into a stable_iterator. 389 stable_iterator stabilize(iterator it) const; 390 391 /// Turn a stable reference to a scope depth into a unstable pointer 392 /// to the EH stack. 393 iterator find(stable_iterator save) const; 394 395 /// Add a branch fixup to the current cleanup scope. 396 BranchFixup &addBranchFixup() { 397 assert(hasNormalCleanups() && "adding fixup in scope without cleanups"); 398 BranchFixups.push_back(BranchFixup()); 399 return BranchFixups.back(); 400 } 401 402 unsigned getNumBranchFixups() const { return BranchFixups.size(); } 403 BranchFixup &getBranchFixup(unsigned I) { 404 assert(I < getNumBranchFixups()); 405 return BranchFixups[I]; 406 } 407 408 /// Pops lazily-removed fixups from the end of the list. This 409 /// should only be called by procedures which have just popped a 410 /// cleanup or resolved one or more fixups. 411 void popNullFixups(); 412 413 /// Clears the branch-fixups list. This should only be called by 414 /// ResolveAllBranchFixups. 415 void clearFixups() { BranchFixups.clear(); } 416 }; 417 418 } // namespace CodeGen 419 } // namespace clang 420 421 #endif 422