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
25namespace clang {
26namespace CodeGen {
27
28class 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.
36struct 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
55template <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.
65template <class T> struct DominatingValue : InvariantValue<T> {};
66
67template <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>
71struct DominatingPointer;
72template <class T> struct DominatingPointer<T,false> : InvariantValue<T*> {};
73// template <class T> struct DominatingPointer<T,true> at end of file
74
75template <class T> struct DominatingValue<T*> : DominatingPointer<T> {};
76
77enum 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.
94class EHScopeStack {
95public:
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 Cleanup() = default;
152
153 virtual bool isRedundantBeforeReturn() { return false; }
154
155 /// Generation flags.
156 class Flags {
157 enum {
158 F_IsForEH = 0x1,
159 F_IsNormalCleanupKind = 0x2,
160 F_IsEHCleanupKind = 0x4,
161 F_HasExitSwitch = 0x8,
162 };
163 unsigned flags;
164
165 public:
166 Flags() : flags(0) {}
167
168 /// isForEH - true if the current emission is for an EH cleanup.
169 bool isForEHCleanup() const { return flags & F_IsForEH; }
170 bool isForNormalCleanup() const { return !isForEHCleanup(); }
171 void setIsForEHCleanup() { flags |= F_IsForEH; }
172
173 bool isNormalCleanupKind() const { return flags & F_IsNormalCleanupKind; }
174 void setIsNormalCleanupKind() { flags |= F_IsNormalCleanupKind; }
175
176 /// isEHCleanupKind - true if the cleanup was pushed as an EH
177 /// cleanup.
178 bool isEHCleanupKind() const { return flags & F_IsEHCleanupKind; }
179 void setIsEHCleanupKind() { flags |= F_IsEHCleanupKind; }
180
181 bool hasExitSwitch() const { return flags & F_HasExitSwitch; }
182 void setHasExitSwitch() { flags |= F_HasExitSwitch; }
183 };
184
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.
189 ///
190 // \param flags cleanup kind.
191 virtual void Emit(CodeGenFunction &CGF, Flags flags) = 0;
192 };
193
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;
199 SavedTuple Saved;
200
201 template <std::size_t... Is>
202 T restore(CodeGenFunction &CGF, std::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))...};
206 }
207
208 void Emit(CodeGenFunction &CGF, Flags flags) override {
209 restore(CGF, std::index_sequence_for<As...>()).Emit(CGF, flags);
210 }
211
212 public:
213 ConditionalCleanup(typename DominatingValue<As>::saved_type... A)
214 : Saved(A...) {}
215
216 ConditionalCleanup(SavedTuple Tuple) : Saved(std::move(Tuple)) {}
217 };
218
219private:
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.
223
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.
227 char *StartOfBuffer;
228
229 /// The end of the buffer.
230 char *EndOfBuffer;
231
232 /// The first valid entry in the buffer.
233 char *StartOfData;
234
235 /// The innermost normal cleanup on the stack.
236 stable_iterator InnermostNormalCleanup;
237
238 /// The innermost EH scope on the stack.
239 stable_iterator InnermostEHScope;
240
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.
245 ///
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.
250 ///
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
254 /// goto foo;
255 /// A a;
256 /// foo:
257 /// bar();
258 SmallVector<BranchFixup, 8> BranchFixups;
259
260 char *allocate(size_t Size);
261 void deallocate(size_t Size);
262
263 void *pushCleanup(CleanupKind K, size_t DataSize);
264
265public:
266 EHScopeStack() : StartOfBuffer(nullptr), EndOfBuffer(nullptr),
267 StartOfData(nullptr), InnermostNormalCleanup(stable_end()),
268 InnermostEHScope(stable_end()) {}
269 ~EHScopeStack() { delete[] StartOfBuffer; }
270
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...);
277 (void) Obj;
278 }
279
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));
287 (void) Obj;
288 }
289
290 // Feel free to add more variants of the following:
291
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.
297 ///
298 /// The data stored in the extra storage must obey the same
299 /// restrictions as normal cleanup member data.
300 ///
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...);
309 }
310
311 void pushCopyOfCleanup(CleanupKind Kind, const void *Cleanup, size_t Size) {
312 void *Buffer = pushCleanup(Kind, Size);
313 std::memcpy(Buffer, Cleanup, Size);
314 }
315
316 /// Pops a cleanup scope off the stack. This is private to CGCleanup.cpp.
317 void popCleanup();
318
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
321 /// set on it.
322 class EHCatchScope *pushCatch(unsigned NumHandlers);
323
324 /// Pops a catch scope off the stack. This is private to CGException.cpp.
325 void popCatch();
326
327 /// Push an exceptions filter on the stack.
328 class EHFilterScope *pushFilter(unsigned NumFilters);
329
330 /// Pops an exceptions filter off the stack.
331 void popFilter();
332
333 /// Push a terminate handler on the stack.
334 void pushTerminate();
335
336 /// Pops a terminate handler off the stack.
337 void popTerminate();
338
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;
342
343 /// Determines whether the exception-scopes stack is empty.
344 bool empty() const { return StartOfData == EndOfBuffer; }
345
346 bool requiresLandingPad() const;
347
348 /// Determines whether there are any normal cleanups on the stack.
349 bool hasNormalCleanups() const {
350 return InnermostNormalCleanup != stable_end();
351 }
352
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;
357 }
358 stable_iterator getInnermostActiveNormalCleanup() const;
359
360 stable_iterator getInnermostEHScope() const {
361 return InnermostEHScope;
362 }
363
364
365 /// An unstable reference to a scope-stack depth. Invalidated by
366 /// pushes but not pops.
367 class iterator;
368
369 /// Returns an iterator pointing to the innermost EH scope.
370 iterator begin() const;
371
372 /// Returns an iterator pointing to the outermost EH scope.
373 iterator end() const;
374
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
377 /// stack.
378 stable_iterator stable_begin() const {
379 return stable_iterator(EndOfBuffer - StartOfData);
380 }
381
382 /// Create a stable reference to the bottom of the EH stack.
383 static stable_iterator stable_end() {
384 return stable_iterator(0);
385 }
386
387 /// Translates an iterator into a stable_iterator.
388 stable_iterator stabilize(iterator it) const;
389
390 /// Turn a stable reference to a scope depth into a unstable pointer
391 /// to the EH stack.
392 iterator find(stable_iterator save) const;
393
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();
399 }
400
401 unsigned getNumBranchFixups() const { return BranchFixups.size(); }
402 BranchFixup &getBranchFixup(unsigned I) {
403 assert(I < getNumBranchFixups());
404 return BranchFixups[I];
405 }
406
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();
411
412 /// Clears the branch-fixups list. This should only be called by
413 /// ResolveAllBranchFixups.
414 void clearFixups() { BranchFixups.clear(); }
415};
416
417} // namespace CodeGen
418} // namespace clang
419
420#endif
421