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

source code of clang/lib/CodeGen/EHScopeStack.h