1 //===-- EHScopeStack.h - Stack for cleanup IR generation --------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
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.
14 //===----------------------------------------------------------------------===//
16 #ifndef LLVM_CLANG_LIB_CODEGEN_EHSCOPESTACK_H
17 #define LLVM_CLANG_LIB_CODEGEN_EHSCOPESTACK_H
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"
29 class CodeGenFunction;
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.
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;
43 /// The ultimate destination of the branch.
45 /// This can be set to null to indicate that this fixup was
46 /// successfully resolved.
47 llvm::BasicBlock *Destination;
49 /// The destination index value.
50 unsigned DestinationIndex;
52 /// The initial branch of the fixup.
53 llvm::BranchInst *InitialBranch;
56 template <class T> struct InvariantValue {
59 static bool needsSaving(type value) { return false; }
60 static saved_type save(CodeGenFunction &CGF, type value) { return value; }
61 static type restore(CodeGenFunction &CGF, saved_type value) { return value; }
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> {};
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
76 template <class T> struct DominatingValue<T*> : DominatingPointer<T> {};
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, ).
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, ...).
87 NormalAndEHCleanup = EHCleanup | NormalCleanup,
89 InactiveCleanup = 0x4,
90 InactiveEHCleanup = EHCleanup | InactiveCleanup,
91 InactiveNormalCleanup = NormalCleanup | InactiveCleanup,
92 InactiveNormalAndEHCleanup = NormalAndEHCleanup | InactiveCleanup,
95 NormalEHLifetimeMarker = LifetimeMarker | NormalAndEHCleanup,
98 /// A stack of scopes which respond to exceptions, including cleanups
102 /* Should switch to alignof(uint64_t) instead of 8, when EHCleanupScope can */
103 enum { ScopeStackAlignment = 8 };
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;
110 /// Offset from StartOfData to EndOfBuffer.
113 stable_iterator(ptrdiff_t Size) : Size(Size) {}
116 static stable_iterator invalid() { return stable_iterator(-1); }
117 stable_iterator() : Size(-1) {}
119 bool isValid() const { return Size >= 0; }
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; }
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; }
132 friend bool operator==(stable_iterator A, stable_iterator B) {
133 return A.Size == B.Size;
135 friend bool operator!=(stable_iterator A, stable_iterator B) {
136 return A.Size != B.Size;
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
145 /// Cleanup implementations should generally be declared in an
146 /// anonymous namespace.
148 // Anchor the construction vtable.
149 virtual void anchor();
152 ~Cleanup() = default;
155 Cleanup(const Cleanup &) = default;
156 Cleanup(Cleanup &&) {}
159 /// Generation flags.
163 F_IsNormalCleanupKind = 0x2,
164 F_IsEHCleanupKind = 0x4
169 Flags() : flags(0) {}
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; }
176 bool isNormalCleanupKind() const { return flags & F_IsNormalCleanupKind; }
177 void setIsNormalCleanupKind() { flags |= F_IsNormalCleanupKind; }
179 /// isEHCleanupKind - true if the cleanup was pushed as an EH
181 bool isEHCleanupKind() const { return flags & F_IsEHCleanupKind; }
182 void setIsEHCleanupKind() { flags |= F_IsEHCleanupKind; }
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.
191 // \param flags cleanup kind.
192 virtual void Emit(CodeGenFunction &CGF, Flags flags) = 0;
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;
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))...};
209 void Emit(CodeGenFunction &CGF, Flags flags) override {
210 restore(CGF, llvm::index_sequence_for<As...>()).Emit(CGF, flags);
214 ConditionalCleanup(typename DominatingValue<As>::saved_type... A)
217 ConditionalCleanup(SavedTuple Tuple) : Saved(std::move(Tuple)) {}
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.
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.
230 /// The end of the buffer.
233 /// The first valid entry in the buffer.
236 /// The innermost normal cleanup on the stack.
237 stable_iterator InnermostNormalCleanup;
239 /// The innermost EH scope on the stack.
240 stable_iterator InnermostEHScope;
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.
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.
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
259 SmallVector<BranchFixup, 8> BranchFixups;
261 char *allocate(size_t Size);
262 void deallocate(size_t Size);
264 void *pushCleanup(CleanupKind K, size_t DataSize);
267 EHScopeStack() : StartOfBuffer(nullptr), EndOfBuffer(nullptr),
268 StartOfData(nullptr), InnermostNormalCleanup(stable_end()),
269 InnermostEHScope(stable_end()) {}
270 ~EHScopeStack() { delete[] StartOfBuffer; }
272 /// Push a lazily-created cleanup on the stack.
273 template <class T, class... As> void pushCleanup(CleanupKind Kind, As... A) {
274 static_assert(alignof(T) <= ScopeStackAlignment,
275 "Cleanup's alignment is too large.");
276 void *Buffer = pushCleanup(Kind, sizeof(T));
277 Cleanup *Obj = new (Buffer) T(A...);
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(alignof(T) <= ScopeStackAlignment,
285 "Cleanup's alignment is too large.");
286 void *Buffer = pushCleanup(Kind, sizeof(T));
287 Cleanup *Obj = new (Buffer) T(std::move(A));
291 // Feel free to add more variants of the following:
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.
299 /// The data stored in the extra storage must obey the same
300 /// restrictions as normal cleanup member data.
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(alignof(T) <= 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...);
312 void pushCopyOfCleanup(CleanupKind Kind, const void *Cleanup, size_t Size) {
313 void *Buffer = pushCleanup(Kind, Size);
314 std::memcpy(Buffer, Cleanup, Size);
317 /// Pops a cleanup scope off the stack. This is private to CGCleanup.cpp.
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
323 class EHCatchScope *pushCatch(unsigned NumHandlers);
325 /// Pops a catch scope off the stack. This is private to CGException.cpp.
328 /// Push an exceptions filter on the stack.
329 class EHFilterScope *pushFilter(unsigned NumFilters);
331 /// Pops an exceptions filter off the stack.
334 /// Push a terminate handler on the stack.
335 void pushTerminate();
337 /// Pops a terminate handler off the stack.
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;
344 /// Determines whether the exception-scopes stack is empty.
345 bool empty() const { return StartOfData == EndOfBuffer; }
347 bool requiresLandingPad() const;
349 /// Determines whether there are any normal cleanups on the stack.
350 bool hasNormalCleanups() const {
351 return InnermostNormalCleanup != stable_end();
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;
359 stable_iterator getInnermostActiveNormalCleanup() const;
361 stable_iterator getInnermostEHScope() const {
362 return InnermostEHScope;
366 /// An unstable reference to a scope-stack depth. Invalidated by
367 /// pushes but not pops.
370 /// Returns an iterator pointing to the innermost EH scope.
371 iterator begin() const;
373 /// Returns an iterator pointing to the outermost EH scope.
374 iterator end() const;
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
379 stable_iterator stable_begin() const {
380 return stable_iterator(EndOfBuffer - StartOfData);
383 /// Create a stable reference to the bottom of the EH stack.
384 static stable_iterator stable_end() {
385 return stable_iterator(0);
388 /// Translates an iterator into a stable_iterator.
389 stable_iterator stabilize(iterator it) const;
391 /// Turn a stable reference to a scope depth into a unstable pointer
393 iterator find(stable_iterator save) const;
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();
402 unsigned getNumBranchFixups() const { return BranchFixups.size(); }
403 BranchFixup &getBranchFixup(unsigned I) {
404 assert(I < getNumBranchFixups());
405 return BranchFixups[I];
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();
413 /// Clears the branch-fixups list. This should only be called by
414 /// ResolveAllBranchFixups.
415 void clearFixups() { BranchFixups.clear(); }
418 } // namespace CodeGen