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,
89 NormalEHLifetimeMarker = LifetimeMarker | NormalAndEHCleanup,
92 /// A stack of scopes which respond to exceptions, including cleanups
96 /* Should switch to alignof(uint64_t) instead of 8, when EHCleanupScope can */
97 enum { ScopeStackAlignment = 8 };
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;
104 /// Offset from StartOfData to EndOfBuffer.
107 stable_iterator(ptrdiff_t Size) : Size(Size) {}
110 static stable_iterator invalid() { return stable_iterator(-1); }
111 stable_iterator() : Size(-1) {}
113 bool isValid() const { return Size >= 0; }
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; }
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; }
126 friend bool operator==(stable_iterator A, stable_iterator B) {
127 return A.Size == B.Size;
129 friend bool operator!=(stable_iterator A, stable_iterator B) {
130 return A.Size != B.Size;
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
139 /// Cleanup implementations should generally be declared in an
140 /// anonymous namespace.
142 // Anchor the construction vtable.
143 virtual void anchor();
146 ~Cleanup() = default;
149 Cleanup(const Cleanup &) = default;
150 Cleanup(Cleanup &&) {}
153 /// Generation flags.
157 F_IsNormalCleanupKind = 0x2,
158 F_IsEHCleanupKind = 0x4,
159 F_HasExitSwitch = 0x8,
164 Flags() : flags(0) {}
166 /// isForEH - true if the current emission is for an EH cleanup.
167 bool isForEHCleanup() const { return flags & F_IsForEH; }
168 bool isForNormalCleanup() const { return !isForEHCleanup(); }
169 void setIsForEHCleanup() { flags |= F_IsForEH; }
171 bool isNormalCleanupKind() const { return flags & F_IsNormalCleanupKind; }
172 void setIsNormalCleanupKind() { flags |= F_IsNormalCleanupKind; }
174 /// isEHCleanupKind - true if the cleanup was pushed as an EH
176 bool isEHCleanupKind() const { return flags & F_IsEHCleanupKind; }
177 void setIsEHCleanupKind() { flags |= F_IsEHCleanupKind; }
179 bool hasExitSwitch() const { return flags & F_HasExitSwitch; }
180 void setHasExitSwitch() { flags |= F_HasExitSwitch; }
183 /// Emit the cleanup. For normal cleanups, this is run in the
184 /// same EH context as when the cleanup was pushed, i.e. the
185 /// immediately-enclosing context of the cleanup scope. For
186 /// EH cleanups, this is run in a terminate context.
188 // \param flags cleanup kind.
189 virtual void Emit(CodeGenFunction &CGF, Flags flags) = 0;
192 /// ConditionalCleanup stores the saved form of its parameters,
193 /// then restores them and performs the cleanup.
194 template <class T, class... As>
195 class ConditionalCleanup final : public Cleanup {
196 typedef std::tuple<typename DominatingValue<As>::saved_type...> SavedTuple;
199 template <std::size_t... Is>
200 T restore(CodeGenFunction &CGF, std::index_sequence<Is...>) {
201 // It's important that the restores are emitted in order. The braced init
202 // list guarantees that.
203 return T{DominatingValue<As>::restore(CGF, std::get<Is>(Saved))...};
206 void Emit(CodeGenFunction &CGF, Flags flags) override {
207 restore(CGF, std::index_sequence_for<As...>()).Emit(CGF, flags);
211 ConditionalCleanup(typename DominatingValue<As>::saved_type... A)
214 ConditionalCleanup(SavedTuple Tuple) : Saved(std::move(Tuple)) {}
218 // The implementation for this class is in CGException.h and
219 // CGException.cpp; the definition is here because it's used as a
220 // member of CodeGenFunction.
222 /// The start of the scope-stack buffer, i.e. the allocated pointer
223 /// for the buffer. All of these pointers are either simultaneously
224 /// null or simultaneously valid.
227 /// The end of the buffer.
230 /// The first valid entry in the buffer.
233 /// The innermost normal cleanup on the stack.
234 stable_iterator InnermostNormalCleanup;
236 /// The innermost EH scope on the stack.
237 stable_iterator InnermostEHScope;
239 /// The current set of branch fixups. A branch fixup is a jump to
240 /// an as-yet unemitted label, i.e. a label for which we don't yet
241 /// know the EH stack depth. Whenever we pop a cleanup, we have
242 /// to thread all the current branch fixups through it.
244 /// Fixups are recorded as the Use of the respective branch or
245 /// switch statement. The use points to the final destination.
246 /// When popping out of a cleanup, these uses are threaded through
247 /// the cleanup and adjusted to point to the new cleanup.
249 /// Note that branches are allowed to jump into protected scopes
250 /// in certain situations; e.g. the following code is legal:
251 /// struct A { ~A(); }; // trivial ctor, non-trivial dtor
256 SmallVector<BranchFixup, 8> BranchFixups;
258 char *allocate(size_t Size);
259 void deallocate(size_t Size);
261 void *pushCleanup(CleanupKind K, size_t DataSize);
264 EHScopeStack() : StartOfBuffer(nullptr), EndOfBuffer(nullptr),
265 StartOfData(nullptr), InnermostNormalCleanup(stable_end()),
266 InnermostEHScope(stable_end()) {}
267 ~EHScopeStack() { delete[] StartOfBuffer; }
269 /// Push a lazily-created cleanup on the stack.
270 template <class T, class... As> void pushCleanup(CleanupKind Kind, As... A) {
271 static_assert(alignof(T) <= ScopeStackAlignment,
272 "Cleanup's alignment is too large.");
273 void *Buffer = pushCleanup(Kind, sizeof(T));
274 Cleanup *Obj = new (Buffer) T(A...);
278 /// Push a lazily-created cleanup on the stack. Tuple version.
279 template <class T, class... As>
280 void pushCleanupTuple(CleanupKind Kind, std::tuple<As...> A) {
281 static_assert(alignof(T) <= ScopeStackAlignment,
282 "Cleanup's alignment is too large.");
283 void *Buffer = pushCleanup(Kind, sizeof(T));
284 Cleanup *Obj = new (Buffer) T(std::move(A));
288 // Feel free to add more variants of the following:
290 /// Push a cleanup with non-constant storage requirements on the
291 /// stack. The cleanup type must provide an additional static method:
292 /// static size_t getExtraSize(size_t);
293 /// The argument to this method will be the value N, which will also
294 /// be passed as the first argument to the constructor.
296 /// The data stored in the extra storage must obey the same
297 /// restrictions as normal cleanup member data.
299 /// The pointer returned from this method is valid until the cleanup
300 /// stack is modified.
301 template <class T, class... As>
302 T *pushCleanupWithExtra(CleanupKind Kind, size_t N, As... A) {
303 static_assert(alignof(T) <= ScopeStackAlignment,
304 "Cleanup's alignment is too large.");
305 void *Buffer = pushCleanup(Kind, sizeof(T) + T::getExtraSize(N));
306 return new (Buffer) T(N, A...);
309 void pushCopyOfCleanup(CleanupKind Kind, const void *Cleanup, size_t Size) {
310 void *Buffer = pushCleanup(Kind, Size);
311 std::memcpy(Buffer, Cleanup, Size);
314 /// Pops a cleanup scope off the stack. This is private to CGCleanup.cpp.
317 /// Push a set of catch handlers on the stack. The catch is
318 /// uninitialized and will need to have the given number of handlers
320 class EHCatchScope *pushCatch(unsigned NumHandlers);
322 /// Pops a catch scope off the stack. This is private to CGException.cpp.
325 /// Push an exceptions filter on the stack.
326 class EHFilterScope *pushFilter(unsigned NumFilters);
328 /// Pops an exceptions filter off the stack.
331 /// Push a terminate handler on the stack.
332 void pushTerminate();
334 /// Pops a terminate handler off the stack.
337 // Returns true iff the current scope is either empty or contains only
338 // lifetime markers, i.e. no real cleanup code
339 bool containsOnlyLifetimeMarkers(stable_iterator Old) const;
341 /// Determines whether the exception-scopes stack is empty.
342 bool empty() const { return StartOfData == EndOfBuffer; }
344 bool requiresLandingPad() const;
346 /// Determines whether there are any normal cleanups on the stack.
347 bool hasNormalCleanups() const {
348 return InnermostNormalCleanup != stable_end();
351 /// Returns the innermost normal cleanup on the stack, or
352 /// stable_end() if there are no normal cleanups.
353 stable_iterator getInnermostNormalCleanup() const {
354 return InnermostNormalCleanup;
356 stable_iterator getInnermostActiveNormalCleanup() const;
358 stable_iterator getInnermostEHScope() const {
359 return InnermostEHScope;
363 /// An unstable reference to a scope-stack depth. Invalidated by
364 /// pushes but not pops.
367 /// Returns an iterator pointing to the innermost EH scope.
368 iterator begin() const;
370 /// Returns an iterator pointing to the outermost EH scope.
371 iterator end() const;
373 /// Create a stable reference to the top of the EH stack. The
374 /// returned reference is valid until that scope is popped off the
376 stable_iterator stable_begin() const {
377 return stable_iterator(EndOfBuffer - StartOfData);
380 /// Create a stable reference to the bottom of the EH stack.
381 static stable_iterator stable_end() {
382 return stable_iterator(0);
385 /// Translates an iterator into a stable_iterator.
386 stable_iterator stabilize(iterator it) const;
388 /// Turn a stable reference to a scope depth into a unstable pointer
390 iterator find(stable_iterator save) const;
392 /// Add a branch fixup to the current cleanup scope.
393 BranchFixup &addBranchFixup() {
394 assert(hasNormalCleanups() && "adding fixup in scope without cleanups");
395 BranchFixups.push_back(BranchFixup());
396 return BranchFixups.back();
399 unsigned getNumBranchFixups() const { return BranchFixups.size(); }
400 BranchFixup &getBranchFixup(unsigned I) {
401 assert(I < getNumBranchFixups());
402 return BranchFixups[I];
405 /// Pops lazily-removed fixups from the end of the list. This
406 /// should only be called by procedures which have just popped a
407 /// cleanup or resolved one or more fixups.
408 void popNullFixups();
410 /// Clears the branch-fixups list. This should only be called by
411 /// ResolveAllBranchFixups.
412 void clearFixups() { BranchFixups.clear(); }
415 } // namespace CodeGen