1 //===-- EHScopeStack.h - Stack for cleanup IR generation --------*- C++ -*-===//
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
7 //===----------------------------------------------------------------------===//
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.
13 //===----------------------------------------------------------------------===//
15 #ifndef LLVM_CLANG_LIB_CODEGEN_EHSCOPESTACK_H
16 #define LLVM_CLANG_LIB_CODEGEN_EHSCOPESTACK_H
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"
28 class CodeGenFunction;
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.
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;
42 /// The ultimate destination of the branch.
44 /// This can be set to null to indicate that this fixup was
45 /// successfully resolved.
46 llvm::BasicBlock *Destination;
48 /// The destination index value.
49 unsigned DestinationIndex;
51 /// The initial branch of the fixup.
52 llvm::BranchInst *InitialBranch;
55 template <class T> struct InvariantValue {
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; }
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> {};
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
75 template <class T> struct DominatingValue<T*> : DominatingPointer<T> {};
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, ).
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, ...).
86 NormalAndEHCleanup = EHCleanup | NormalCleanup,
88 InactiveCleanup = 0x4,
89 InactiveEHCleanup = EHCleanup | InactiveCleanup,
90 InactiveNormalCleanup = NormalCleanup | InactiveCleanup,
91 InactiveNormalAndEHCleanup = NormalAndEHCleanup | InactiveCleanup,
94 NormalEHLifetimeMarker = LifetimeMarker | NormalAndEHCleanup,
97 /// A stack of scopes which respond to exceptions, including cleanups
101 /* Should switch to alignof(uint64_t) instead of 8, when EHCleanupScope can */
102 enum { ScopeStackAlignment = 8 };
104 /// A saved depth on the scope stack. This is necessary because
105 /// pushing scopes onto the stack invalidates iterators.
106 class stable_iterator {
107 friend class EHScopeStack;
109 /// Offset from StartOfData to EndOfBuffer.
112 stable_iterator(ptrdiff_t Size) : Size(Size) {}
115 static stable_iterator invalid() { return stable_iterator(-1); }
116 stable_iterator() : Size(-1) {}
118 bool isValid() const { return Size >= 0; }
120 /// Returns true if this scope encloses I.
121 /// Returns false if I is invalid.
122 /// This scope must be valid.
123 bool encloses(stable_iterator I) const { return Size <= I.Size; }
125 /// Returns true if this scope strictly encloses I: that is,
126 /// if it encloses I and is not I.
127 /// Returns false is I is invalid.
128 /// This scope must be valid.
129 bool strictlyEncloses(stable_iterator I) const { return Size < I.Size; }
131 friend bool operator==(stable_iterator A, stable_iterator B) {
132 return A.Size == B.Size;
134 friend bool operator!=(stable_iterator A, stable_iterator B) {
135 return A.Size != B.Size;
139 /// Information for lazily generating a cleanup. Subclasses must be
140 /// POD-like: cleanups will not be destructed, and they will be
141 /// allocated on the cleanup stack and freely copied and moved
144 /// Cleanup implementations should generally be declared in an
145 /// anonymous namespace.
147 // Anchor the construction vtable.
148 virtual void anchor();
151 ~Cleanup() = default;
154 Cleanup(const Cleanup &) = default;
155 Cleanup(Cleanup &&) {}
158 /// Generation flags.
162 F_IsNormalCleanupKind = 0x2,
163 F_IsEHCleanupKind = 0x4
168 Flags() : flags(0) {}
170 /// isForEH - true if the current emission is for an EH cleanup.
171 bool isForEHCleanup() const { return flags & F_IsForEH; }
172 bool isForNormalCleanup() const { return !isForEHCleanup(); }
173 void setIsForEHCleanup() { flags |= F_IsForEH; }
175 bool isNormalCleanupKind() const { return flags & F_IsNormalCleanupKind; }
176 void setIsNormalCleanupKind() { flags |= F_IsNormalCleanupKind; }
178 /// isEHCleanupKind - true if the cleanup was pushed as an EH
180 bool isEHCleanupKind() const { return flags & F_IsEHCleanupKind; }
181 void setIsEHCleanupKind() { flags |= F_IsEHCleanupKind; }
185 /// Emit the cleanup. For normal cleanups, this is run in the
186 /// same EH context as when the cleanup was pushed, i.e. the
187 /// immediately-enclosing context of the cleanup scope. For
188 /// EH cleanups, this is run in a terminate context.
190 // \param flags cleanup kind.
191 virtual void Emit(CodeGenFunction &CGF, Flags flags) = 0;
194 /// ConditionalCleanup stores the saved form of its parameters,
195 /// then restores them and performs the cleanup.
196 template <class T, class... As>
197 class ConditionalCleanup final : public Cleanup {
198 typedef std::tuple<typename DominatingValue<As>::saved_type...> SavedTuple;
201 template <std::size_t... Is>
202 T restore(CodeGenFunction &CGF, llvm::index_sequence<Is...>) {
203 // It's important that the restores are emitted in order. The braced init
204 // list guarantees that.
205 return T{DominatingValue<As>::restore(CGF, std::get<Is>(Saved))...};
208 void Emit(CodeGenFunction &CGF, Flags flags) override {
209 restore(CGF, llvm::index_sequence_for<As...>()).Emit(CGF, flags);
213 ConditionalCleanup(typename DominatingValue<As>::saved_type... A)
216 ConditionalCleanup(SavedTuple Tuple) : Saved(std::move(Tuple)) {}
220 // The implementation for this class is in CGException.h and
221 // CGException.cpp; the definition is here because it's used as a
222 // member of CodeGenFunction.
224 /// The start of the scope-stack buffer, i.e. the allocated pointer
225 /// for the buffer. All of these pointers are either simultaneously
226 /// null or simultaneously valid.
229 /// The end of the buffer.
232 /// The first valid entry in the buffer.
235 /// The innermost normal cleanup on the stack.
236 stable_iterator InnermostNormalCleanup;
238 /// The innermost EH scope on the stack.
239 stable_iterator InnermostEHScope;
241 /// The current set of branch fixups. A branch fixup is a jump to
242 /// an as-yet unemitted label, i.e. a label for which we don't yet
243 /// know the EH stack depth. Whenever we pop a cleanup, we have
244 /// to thread all the current branch fixups through it.
246 /// Fixups are recorded as the Use of the respective branch or
247 /// switch statement. The use points to the final destination.
248 /// When popping out of a cleanup, these uses are threaded through
249 /// the cleanup and adjusted to point to the new cleanup.
251 /// Note that branches are allowed to jump into protected scopes
252 /// in certain situations; e.g. the following code is legal:
253 /// struct A { ~A(); }; // trivial ctor, non-trivial dtor
258 SmallVector<BranchFixup, 8> BranchFixups;
260 char *allocate(size_t Size);
261 void deallocate(size_t Size);
263 void *pushCleanup(CleanupKind K, size_t DataSize);
266 EHScopeStack() : StartOfBuffer(nullptr), EndOfBuffer(nullptr),
267 StartOfData(nullptr), InnermostNormalCleanup(stable_end()),
268 InnermostEHScope(stable_end()) {}
269 ~EHScopeStack() { delete[] StartOfBuffer; }
271 /// Push a lazily-created cleanup on the stack.
272 template <class T, class... As> void pushCleanup(CleanupKind Kind, As... A) {
273 static_assert(alignof(T) <= ScopeStackAlignment,
274 "Cleanup's alignment is too large.");
275 void *Buffer = pushCleanup(Kind, sizeof(T));
276 Cleanup *Obj = new (Buffer) T(A...);
280 /// Push a lazily-created cleanup on the stack. Tuple version.
281 template <class T, class... As>
282 void pushCleanupTuple(CleanupKind Kind, std::tuple<As...> A) {
283 static_assert(alignof(T) <= ScopeStackAlignment,
284 "Cleanup's alignment is too large.");
285 void *Buffer = pushCleanup(Kind, sizeof(T));
286 Cleanup *Obj = new (Buffer) T(std::move(A));
290 // Feel free to add more variants of the following:
292 /// Push a cleanup with non-constant storage requirements on the
293 /// stack. The cleanup type must provide an additional static method:
294 /// static size_t getExtraSize(size_t);
295 /// The argument to this method will be the value N, which will also
296 /// be passed as the first argument to the constructor.
298 /// The data stored in the extra storage must obey the same
299 /// restrictions as normal cleanup member data.
301 /// The pointer returned from this method is valid until the cleanup
302 /// stack is modified.
303 template <class T, class... As>
304 T *pushCleanupWithExtra(CleanupKind Kind, size_t N, As... A) {
305 static_assert(alignof(T) <= ScopeStackAlignment,
306 "Cleanup's alignment is too large.");
307 void *Buffer = pushCleanup(Kind, sizeof(T) + T::getExtraSize(N));
308 return new (Buffer) T(N, A...);
311 void pushCopyOfCleanup(CleanupKind Kind, const void *Cleanup, size_t Size) {
312 void *Buffer = pushCleanup(Kind, Size);
313 std::memcpy(Buffer, Cleanup, Size);
316 /// Pops a cleanup scope off the stack. This is private to CGCleanup.cpp.
319 /// Push a set of catch handlers on the stack. The catch is
320 /// uninitialized and will need to have the given number of handlers
322 class EHCatchScope *pushCatch(unsigned NumHandlers);
324 /// Pops a catch scope off the stack. This is private to CGException.cpp.
327 /// Push an exceptions filter on the stack.
328 class EHFilterScope *pushFilter(unsigned NumFilters);
330 /// Pops an exceptions filter off the stack.
333 /// Push a terminate handler on the stack.
334 void pushTerminate();
336 /// Pops a terminate handler off the stack.
339 // Returns true iff the current scope is either empty or contains only
340 // lifetime markers, i.e. no real cleanup code
341 bool containsOnlyLifetimeMarkers(stable_iterator Old) const;
343 /// Determines whether the exception-scopes stack is empty.
344 bool empty() const { return StartOfData == EndOfBuffer; }
346 bool requiresLandingPad() const;
348 /// Determines whether there are any normal cleanups on the stack.
349 bool hasNormalCleanups() const {
350 return InnermostNormalCleanup != stable_end();
353 /// Returns the innermost normal cleanup on the stack, or
354 /// stable_end() if there are no normal cleanups.
355 stable_iterator getInnermostNormalCleanup() const {
356 return InnermostNormalCleanup;
358 stable_iterator getInnermostActiveNormalCleanup() const;
360 stable_iterator getInnermostEHScope() const {
361 return InnermostEHScope;
365 /// An unstable reference to a scope-stack depth. Invalidated by
366 /// pushes but not pops.
369 /// Returns an iterator pointing to the innermost EH scope.
370 iterator begin() const;
372 /// Returns an iterator pointing to the outermost EH scope.
373 iterator end() const;
375 /// Create a stable reference to the top of the EH stack. The
376 /// returned reference is valid until that scope is popped off the
378 stable_iterator stable_begin() const {
379 return stable_iterator(EndOfBuffer - StartOfData);
382 /// Create a stable reference to the bottom of the EH stack.
383 static stable_iterator stable_end() {
384 return stable_iterator(0);
387 /// Translates an iterator into a stable_iterator.
388 stable_iterator stabilize(iterator it) const;
390 /// Turn a stable reference to a scope depth into a unstable pointer
392 iterator find(stable_iterator save) const;
394 /// Add a branch fixup to the current cleanup scope.
395 BranchFixup &addBranchFixup() {
396 assert(hasNormalCleanups() && "adding fixup in scope without cleanups");
397 BranchFixups.push_back(BranchFixup());
398 return BranchFixups.back();
401 unsigned getNumBranchFixups() const { return BranchFixups.size(); }
402 BranchFixup &getBranchFixup(unsigned I) {
403 assert(I < getNumBranchFixups());
404 return BranchFixups[I];
407 /// Pops lazily-removed fixups from the end of the list. This
408 /// should only be called by procedures which have just popped a
409 /// cleanup or resolved one or more fixups.
410 void popNullFixups();
412 /// Clears the branch-fixups list. This should only be called by
413 /// ResolveAllBranchFixups.
414 void clearFixups() { BranchFixups.clear(); }
417 } // namespace CodeGen