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 // FakeUse needs to be recognized as a special cleanup similar to lifetime
92 // markers chiefly to be ignored in most contexts.
93 FakeUse = 0x10,
94 NormalFakeUse = FakeUse | NormalCleanup,
95};
96
97/// A stack of scopes which respond to exceptions, including cleanups
98/// and catch blocks.
99class EHScopeStack {
100public:
101 /* Should switch to alignof(uint64_t) instead of 8, when EHCleanupScope can */
102 enum { ScopeStackAlignment = 8 };
103
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;
108
109 /// Offset from StartOfData to EndOfBuffer.
110 ptrdiff_t Size;
111
112 stable_iterator(ptrdiff_t Size) : Size(Size) {}
113
114 public:
115 static stable_iterator invalid() { return stable_iterator(-1); }
116 stable_iterator() : Size(-1) {}
117
118 bool isValid() const { return Size >= 0; }
119
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; }
124
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; }
130
131 friend bool operator==(stable_iterator A, stable_iterator B) {
132 return A.Size == B.Size;
133 }
134 friend bool operator!=(stable_iterator A, stable_iterator B) {
135 return A.Size != B.Size;
136 }
137 };
138
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
142 /// around.
143 ///
144 /// Cleanup implementations should generally be declared in an
145 /// anonymous namespace.
146 class Cleanup {
147 // Anchor the construction vtable.
148 virtual void anchor();
149
150 protected:
151 ~Cleanup() = default;
152
153 public:
154 Cleanup(const Cleanup &) = default;
155 Cleanup(Cleanup &&) {}
156
157 // The copy and move assignment operator is defined as deleted pending
158 // further motivation.
159 Cleanup &operator=(const Cleanup &) = delete;
160 Cleanup &operator=(Cleanup &&) = delete;
161
162 Cleanup() = default;
163
164 virtual bool isRedundantBeforeReturn() { return false; }
165
166 /// Generation flags.
167 class Flags {
168 enum {
169 F_IsForEH = 0x1,
170 F_IsNormalCleanupKind = 0x2,
171 F_IsEHCleanupKind = 0x4,
172 F_HasExitSwitch = 0x8,
173 };
174 unsigned flags = 0;
175
176 public:
177 Flags() = default;
178
179 /// isForEH - true if the current emission is for an EH cleanup.
180 bool isForEHCleanup() const { return flags & F_IsForEH; }
181 bool isForNormalCleanup() const { return !isForEHCleanup(); }
182 void setIsForEHCleanup() { flags |= F_IsForEH; }
183
184 bool isNormalCleanupKind() const { return flags & F_IsNormalCleanupKind; }
185 void setIsNormalCleanupKind() { flags |= F_IsNormalCleanupKind; }
186
187 /// isEHCleanupKind - true if the cleanup was pushed as an EH
188 /// cleanup.
189 bool isEHCleanupKind() const { return flags & F_IsEHCleanupKind; }
190 void setIsEHCleanupKind() { flags |= F_IsEHCleanupKind; }
191
192 bool hasExitSwitch() const { return flags & F_HasExitSwitch; }
193 void setHasExitSwitch() { flags |= F_HasExitSwitch; }
194 };
195
196 /// Emit the cleanup. For normal cleanups, this is run in the
197 /// same EH context as when the cleanup was pushed, i.e. the
198 /// immediately-enclosing context of the cleanup scope. For
199 /// EH cleanups, this is run in a terminate context.
200 ///
201 // \param flags cleanup kind.
202 virtual void Emit(CodeGenFunction &CGF, Flags flags) = 0;
203 };
204
205 /// ConditionalCleanup stores the saved form of its parameters,
206 /// then restores them and performs the cleanup.
207 template <class T, class... As>
208 class ConditionalCleanup final : public Cleanup {
209 typedef std::tuple<typename DominatingValue<As>::saved_type...> SavedTuple;
210 SavedTuple Saved;
211
212 template <std::size_t... Is>
213 T restore(CodeGenFunction &CGF, std::index_sequence<Is...>) {
214 // It's important that the restores are emitted in order. The braced init
215 // list guarantees that.
216 return T{DominatingValue<As>::restore(CGF, std::get<Is>(Saved))...};
217 }
218
219 void Emit(CodeGenFunction &CGF, Flags flags) override {
220 restore(CGF, std::index_sequence_for<As...>()).Emit(CGF, flags);
221 }
222
223 public:
224 ConditionalCleanup(typename DominatingValue<As>::saved_type... A)
225 : Saved(A...) {}
226
227 ConditionalCleanup(SavedTuple Tuple) : Saved(std::move(Tuple)) {}
228 };
229
230private:
231 // The implementation for this class is in CGException.h and
232 // CGException.cpp; the definition is here because it's used as a
233 // member of CodeGenFunction.
234
235 /// The start of the scope-stack buffer, i.e. the allocated pointer
236 /// for the buffer. All of these pointers are either simultaneously
237 /// null or simultaneously valid.
238 char *StartOfBuffer;
239
240 /// The end of the buffer.
241 char *EndOfBuffer;
242
243 /// The first valid entry in the buffer.
244 char *StartOfData;
245
246 /// The innermost normal cleanup on the stack.
247 stable_iterator InnermostNormalCleanup;
248
249 /// The innermost EH scope on the stack.
250 stable_iterator InnermostEHScope;
251
252 /// The CGF this Stack belong to
253 CodeGenFunction* CGF;
254
255 /// The current set of branch fixups. A branch fixup is a jump to
256 /// an as-yet unemitted label, i.e. a label for which we don't yet
257 /// know the EH stack depth. Whenever we pop a cleanup, we have
258 /// to thread all the current branch fixups through it.
259 ///
260 /// Fixups are recorded as the Use of the respective branch or
261 /// switch statement. The use points to the final destination.
262 /// When popping out of a cleanup, these uses are threaded through
263 /// the cleanup and adjusted to point to the new cleanup.
264 ///
265 /// Note that branches are allowed to jump into protected scopes
266 /// in certain situations; e.g. the following code is legal:
267 /// struct A { ~A(); }; // trivial ctor, non-trivial dtor
268 /// goto foo;
269 /// A a;
270 /// foo:
271 /// bar();
272 SmallVector<BranchFixup, 8> BranchFixups;
273
274 char *allocate(size_t Size);
275 void deallocate(size_t Size);
276
277 void *pushCleanup(CleanupKind K, size_t DataSize);
278
279public:
280 EHScopeStack()
281 : StartOfBuffer(nullptr), EndOfBuffer(nullptr), StartOfData(nullptr),
282 InnermostNormalCleanup(stable_end()), InnermostEHScope(stable_end()),
283 CGF(nullptr) {}
284 ~EHScopeStack() { delete[] StartOfBuffer; }
285
286 EHScopeStack(const EHScopeStack &) = delete;
287 EHScopeStack &operator=(const EHScopeStack &) = delete;
288
289 /// Push a lazily-created cleanup on the stack.
290 template <class T, class... As> void pushCleanup(CleanupKind Kind, As... A) {
291 static_assert(alignof(T) <= ScopeStackAlignment,
292 "Cleanup's alignment is too large.");
293 void *Buffer = pushCleanup(K: Kind, DataSize: sizeof(T));
294 Cleanup *Obj = new (Buffer) T(A...);
295 (void) Obj;
296 }
297
298 /// Push a lazily-created cleanup on the stack. Tuple version.
299 template <class T, class... As>
300 void pushCleanupTuple(CleanupKind Kind, std::tuple<As...> A) {
301 static_assert(alignof(T) <= ScopeStackAlignment,
302 "Cleanup's alignment is too large.");
303 void *Buffer = pushCleanup(K: Kind, DataSize: sizeof(T));
304 Cleanup *Obj = new (Buffer) T(std::move(A));
305 (void) Obj;
306 }
307
308 // Feel free to add more variants of the following:
309
310 /// Push a cleanup with non-constant storage requirements on the
311 /// stack. The cleanup type must provide an additional static method:
312 /// static size_t getExtraSize(size_t);
313 /// The argument to this method will be the value N, which will also
314 /// be passed as the first argument to the constructor.
315 ///
316 /// The data stored in the extra storage must obey the same
317 /// restrictions as normal cleanup member data.
318 ///
319 /// The pointer returned from this method is valid until the cleanup
320 /// stack is modified.
321 template <class T, class... As>
322 T *pushCleanupWithExtra(CleanupKind Kind, size_t N, As... A) {
323 static_assert(alignof(T) <= ScopeStackAlignment,
324 "Cleanup's alignment is too large.");
325 void *Buffer = pushCleanup(Kind, sizeof(T) + T::getExtraSize(N));
326 return new (Buffer) T(N, A...);
327 }
328
329 void pushCopyOfCleanup(CleanupKind Kind, const void *Cleanup, size_t Size) {
330 void *Buffer = pushCleanup(K: Kind, DataSize: Size);
331 std::memcpy(dest: Buffer, src: Cleanup, n: Size);
332 }
333
334 void setCGF(CodeGenFunction *inCGF) { CGF = inCGF; }
335
336 /// Pops a cleanup scope off the stack. This is private to CGCleanup.cpp.
337 void popCleanup();
338
339 /// Push a set of catch handlers on the stack. The catch is
340 /// uninitialized and will need to have the given number of handlers
341 /// set on it.
342 class EHCatchScope *pushCatch(unsigned NumHandlers);
343
344 /// Pops a catch scope off the stack. This is private to CGException.cpp.
345 void popCatch();
346
347 /// Push an exceptions filter on the stack.
348 class EHFilterScope *pushFilter(unsigned NumFilters);
349
350 /// Pops an exceptions filter off the stack.
351 void popFilter();
352
353 /// Push a terminate handler on the stack.
354 void pushTerminate();
355
356 /// Pops a terminate handler off the stack.
357 void popTerminate();
358
359 // Returns true iff the current scope is either empty or contains only
360 // noop cleanups, i.e. lifetime markers and fake uses.
361 bool containsOnlyNoopCleanups(stable_iterator Old) const;
362
363 /// Determines whether the exception-scopes stack is empty.
364 bool empty() const { return StartOfData == EndOfBuffer; }
365
366 bool requiresLandingPad() const;
367
368 /// Determines whether there are any normal cleanups on the stack.
369 bool hasNormalCleanups() const {
370 return InnermostNormalCleanup != stable_end();
371 }
372
373 /// Returns the innermost normal cleanup on the stack, or
374 /// stable_end() if there are no normal cleanups.
375 stable_iterator getInnermostNormalCleanup() const {
376 return InnermostNormalCleanup;
377 }
378 stable_iterator getInnermostActiveNormalCleanup() const;
379
380 stable_iterator getInnermostEHScope() const {
381 return InnermostEHScope;
382 }
383
384
385 /// An unstable reference to a scope-stack depth. Invalidated by
386 /// pushes but not pops.
387 class iterator;
388
389 /// Returns an iterator pointing to the innermost EH scope.
390 iterator begin() const;
391
392 /// Returns an iterator pointing to the outermost EH scope.
393 iterator end() const;
394
395 /// Create a stable reference to the top of the EH stack. The
396 /// returned reference is valid until that scope is popped off the
397 /// stack.
398 stable_iterator stable_begin() const {
399 return stable_iterator(EndOfBuffer - StartOfData);
400 }
401
402 /// Create a stable reference to the bottom of the EH stack.
403 static stable_iterator stable_end() {
404 return stable_iterator(0);
405 }
406
407 /// Translates an iterator into a stable_iterator.
408 stable_iterator stabilize(iterator it) const;
409
410 /// Turn a stable reference to a scope depth into a unstable pointer
411 /// to the EH stack.
412 iterator find(stable_iterator save) const;
413
414 /// Add a branch fixup to the current cleanup scope.
415 BranchFixup &addBranchFixup() {
416 assert(hasNormalCleanups() && "adding fixup in scope without cleanups");
417 BranchFixups.push_back(Elt: BranchFixup());
418 return BranchFixups.back();
419 }
420
421 unsigned getNumBranchFixups() const { return BranchFixups.size(); }
422 BranchFixup &getBranchFixup(unsigned I) {
423 assert(I < getNumBranchFixups());
424 return BranchFixups[I];
425 }
426
427 /// Pops lazily-removed fixups from the end of the list. This
428 /// should only be called by procedures which have just popped a
429 /// cleanup or resolved one or more fixups.
430 void popNullFixups();
431
432 /// Clears the branch-fixups list. This should only be called by
433 /// ResolveAllBranchFixups.
434 void clearFixups() { BranchFixups.clear(); }
435};
436
437} // namespace CodeGen
438} // namespace clang
439
440#endif
441