clang 17.0.0git
EHScopeStack.h
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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.
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.
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>
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, ...).
85
87
90};
91
92/// A stack of scopes which respond to exceptions, including cleanups
93/// and catch blocks.
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.
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
127 return A.Size == B.Size;
128 }
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;
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:
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 CGF this Stack belong to
242 CodeGenFunction* CGF;
243
244 /// The current set of branch fixups. A branch fixup is a jump to
245 /// an as-yet unemitted label, i.e. a label for which we don't yet
246 /// know the EH stack depth. Whenever we pop a cleanup, we have
247 /// to thread all the current branch fixups through it.
248 ///
249 /// Fixups are recorded as the Use of the respective branch or
250 /// switch statement. The use points to the final destination.
251 /// When popping out of a cleanup, these uses are threaded through
252 /// the cleanup and adjusted to point to the new cleanup.
253 ///
254 /// Note that branches are allowed to jump into protected scopes
255 /// in certain situations; e.g. the following code is legal:
256 /// struct A { ~A(); }; // trivial ctor, non-trivial dtor
257 /// goto foo;
258 /// A a;
259 /// foo:
260 /// bar();
261 SmallVector<BranchFixup, 8> BranchFixups;
262
263 char *allocate(size_t Size);
264 void deallocate(size_t Size);
265
266 void *pushCleanup(CleanupKind K, size_t DataSize);
267
268public:
270 : StartOfBuffer(nullptr), EndOfBuffer(nullptr), StartOfData(nullptr),
271 InnermostNormalCleanup(stable_end()), InnermostEHScope(stable_end()),
272 CGF(nullptr) {}
273 ~EHScopeStack() { delete[] StartOfBuffer; }
274
275 /// Push a lazily-created cleanup on the stack.
276 template <class T, class... As> void pushCleanup(CleanupKind Kind, As... A) {
277 static_assert(alignof(T) <= ScopeStackAlignment,
278 "Cleanup's alignment is too large.");
279 void *Buffer = pushCleanup(Kind, sizeof(T));
280 Cleanup *Obj = new (Buffer) T(A...);
281 (void) Obj;
282 }
283
284 /// Push a lazily-created cleanup on the stack. Tuple version.
285 template <class T, class... As>
286 void pushCleanupTuple(CleanupKind Kind, std::tuple<As...> A) {
287 static_assert(alignof(T) <= ScopeStackAlignment,
288 "Cleanup's alignment is too large.");
289 void *Buffer = pushCleanup(Kind, sizeof(T));
290 Cleanup *Obj = new (Buffer) T(std::move(A));
291 (void) Obj;
292 }
293
294 // Feel free to add more variants of the following:
295
296 /// Push a cleanup with non-constant storage requirements on the
297 /// stack. The cleanup type must provide an additional static method:
298 /// static size_t getExtraSize(size_t);
299 /// The argument to this method will be the value N, which will also
300 /// be passed as the first argument to the constructor.
301 ///
302 /// The data stored in the extra storage must obey the same
303 /// restrictions as normal cleanup member data.
304 ///
305 /// The pointer returned from this method is valid until the cleanup
306 /// stack is modified.
307 template <class T, class... As>
308 T *pushCleanupWithExtra(CleanupKind Kind, size_t N, As... A) {
309 static_assert(alignof(T) <= ScopeStackAlignment,
310 "Cleanup's alignment is too large.");
311 void *Buffer = pushCleanup(Kind, sizeof(T) + T::getExtraSize(N));
312 return new (Buffer) T(N, A...);
313 }
314
315 void pushCopyOfCleanup(CleanupKind Kind, const void *Cleanup, size_t Size) {
316 void *Buffer = pushCleanup(Kind, Size);
317 std::memcpy(Buffer, Cleanup, Size);
318 }
319
320 void setCGF(CodeGenFunction *inCGF) { CGF = inCGF; }
321
322 /// Pops a cleanup scope off the stack. This is private to CGCleanup.cpp.
323 void popCleanup();
324
325 /// Push a set of catch handlers on the stack. The catch is
326 /// uninitialized and will need to have the given number of handlers
327 /// set on it.
328 class EHCatchScope *pushCatch(unsigned NumHandlers);
329
330 /// Pops a catch scope off the stack. This is private to CGException.cpp.
331 void popCatch();
332
333 /// Push an exceptions filter on the stack.
334 class EHFilterScope *pushFilter(unsigned NumFilters);
335
336 /// Pops an exceptions filter off the stack.
337 void popFilter();
338
339 /// Push a terminate handler on the stack.
340 void pushTerminate();
341
342 /// Pops a terminate handler off the stack.
343 void popTerminate();
344
345 // Returns true iff the current scope is either empty or contains only
346 // lifetime markers, i.e. no real cleanup code
347 bool containsOnlyLifetimeMarkers(stable_iterator Old) const;
348
349 /// Determines whether the exception-scopes stack is empty.
350 bool empty() const { return StartOfData == EndOfBuffer; }
351
352 bool requiresLandingPad() const;
353
354 /// Determines whether there are any normal cleanups on the stack.
355 bool hasNormalCleanups() const {
356 return InnermostNormalCleanup != stable_end();
357 }
358
359 /// Returns the innermost normal cleanup on the stack, or
360 /// stable_end() if there are no normal cleanups.
362 return InnermostNormalCleanup;
363 }
364 stable_iterator getInnermostActiveNormalCleanup() const;
365
367 return InnermostEHScope;
368 }
369
370
371 /// An unstable reference to a scope-stack depth. Invalidated by
372 /// pushes but not pops.
373 class iterator;
374
375 /// Returns an iterator pointing to the innermost EH scope.
376 iterator begin() const;
377
378 /// Returns an iterator pointing to the outermost EH scope.
379 iterator end() const;
380
381 /// Create a stable reference to the top of the EH stack. The
382 /// returned reference is valid until that scope is popped off the
383 /// stack.
385 return stable_iterator(EndOfBuffer - StartOfData);
386 }
387
388 /// Create a stable reference to the bottom of the EH stack.
390 return stable_iterator(0);
391 }
392
393 /// Translates an iterator into a stable_iterator.
394 stable_iterator stabilize(iterator it) const;
395
396 /// Turn a stable reference to a scope depth into a unstable pointer
397 /// to the EH stack.
398 iterator find(stable_iterator save) const;
399
400 /// Add a branch fixup to the current cleanup scope.
402 assert(hasNormalCleanups() && "adding fixup in scope without cleanups");
403 BranchFixups.push_back(BranchFixup());
404 return BranchFixups.back();
405 }
406
407 unsigned getNumBranchFixups() const { return BranchFixups.size(); }
409 assert(I < getNumBranchFixups());
410 return BranchFixups[I];
411 }
412
413 /// Pops lazily-removed fixups from the end of the list. This
414 /// should only be called by procedures which have just popped a
415 /// cleanup or resolved one or more fixups.
416 void popNullFixups();
417
418 /// Clears the branch-fixups list. This should only be called by
419 /// ResolveAllBranchFixups.
420 void clearFixups() { BranchFixups.clear(); }
421};
422
423} // namespace CodeGen
424} // namespace clang
425
426#endif
Forward-declares and imports various common LLVM datatypes that clang wants to use unqualified.
CodeGenFunction - This class organizes the per-function state that is used while generating LLVM code...
A scope which attempts to handle some, possibly all, types of exceptions.
Definition: CGCleanup.h:146
An exceptions scope which filters exceptions thrown through it.
Definition: CGCleanup.h:437
bool isEHCleanupKind() const
isEHCleanupKind - true if the cleanup was pushed as an EH cleanup.
Definition: EHScopeStack.h:178
bool isForEHCleanup() const
isForEH - true if the current emission is for an EH cleanup.
Definition: EHScopeStack.h:169
Information for lazily generating a cleanup.
Definition: EHScopeStack.h:141
virtual void Emit(CodeGenFunction &CGF, Flags flags)=0
Emit the cleanup.
Cleanup(const Cleanup &)=default
ConditionalCleanup stores the saved form of its parameters, then restores them and performs the clean...
Definition: EHScopeStack.h:197
ConditionalCleanup(typename DominatingValue< As >::saved_type... A)
Definition: EHScopeStack.h:213
A saved depth on the scope stack.
Definition: EHScopeStack.h:101
bool encloses(stable_iterator I) const
Returns true if this scope encloses I.
Definition: EHScopeStack.h:118
bool strictlyEncloses(stable_iterator I) const
Returns true if this scope strictly encloses I: that is, if it encloses I and is not I.
Definition: EHScopeStack.h:124
friend bool operator==(stable_iterator A, stable_iterator B)
Definition: EHScopeStack.h:126
friend bool operator!=(stable_iterator A, stable_iterator B)
Definition: EHScopeStack.h:129
A stack of scopes which respond to exceptions, including cleanups and catch blocks.
Definition: EHScopeStack.h:94
class EHFilterScope * pushFilter(unsigned NumFilters)
Push an exceptions filter on the stack.
Definition: CGCleanup.cpp:242
BranchFixup & getBranchFixup(unsigned I)
Definition: EHScopeStack.h:408
stable_iterator getInnermostNormalCleanup() const
Returns the innermost normal cleanup on the stack, or stable_end() if there are no normal cleanups.
Definition: EHScopeStack.h:361
void setCGF(CodeGenFunction *inCGF)
Definition: EHScopeStack.h:320
stable_iterator stable_begin() const
Create a stable reference to the top of the EH stack.
Definition: EHScopeStack.h:384
unsigned getNumBranchFixups() const
Definition: EHScopeStack.h:407
void popCleanup()
Pops a cleanup scope off the stack. This is private to CGCleanup.cpp.
Definition: CGCleanup.cpp:217
stable_iterator getInnermostEHScope() const
Definition: EHScopeStack.h:366
void pushCopyOfCleanup(CleanupKind Kind, const void *Cleanup, size_t Size)
Definition: EHScopeStack.h:315
bool containsOnlyLifetimeMarkers(stable_iterator Old) const
Definition: CGCleanup.cpp:144
bool empty() const
Determines whether the exception-scopes stack is empty.
Definition: EHScopeStack.h:350
void pushCleanup(CleanupKind Kind, As... A)
Push a lazily-created cleanup on the stack.
Definition: EHScopeStack.h:276
T * pushCleanupWithExtra(CleanupKind Kind, size_t N, As... A)
Push a cleanup with non-constant storage requirements on the stack.
Definition: EHScopeStack.h:308
iterator end() const
Returns an iterator pointing to the outermost EH scope.
Definition: CGCleanup.h:555
void popFilter()
Pops an exceptions filter off the stack.
Definition: CGCleanup.cpp:250
iterator begin() const
Returns an iterator pointing to the innermost EH scope.
Definition: CGCleanup.h:551
BranchFixup & addBranchFixup()
Add a branch fixup to the current cleanup scope.
Definition: EHScopeStack.h:401
void popCatch()
Pops a catch scope off the stack. This is private to CGException.cpp.
Definition: CGCleanup.h:559
class EHCatchScope * pushCatch(unsigned NumHandlers)
Push a set of catch handlers on the stack.
Definition: CGCleanup.cpp:259
iterator find(stable_iterator save) const
Turn a stable reference to a scope depth into a unstable pointer to the EH stack.
Definition: CGCleanup.h:575
void popNullFixups()
Pops lazily-removed fixups from the end of the list.
Definition: CGCleanup.cpp:278
bool hasNormalCleanups() const
Determines whether there are any normal cleanups on the stack.
Definition: EHScopeStack.h:355
stable_iterator getInnermostActiveNormalCleanup() const
Definition: CGCleanup.cpp:170
stable_iterator stabilize(iterator it) const
Translates an iterator into a stable_iterator.
Definition: CGCleanup.h:582
static stable_iterator stable_end()
Create a stable reference to the bottom of the EH stack.
Definition: EHScopeStack.h:389
void clearFixups()
Clears the branch-fixups list.
Definition: EHScopeStack.h:420
void popTerminate()
Pops a terminate handler off the stack.
Definition: CGCleanup.h:567
void pushTerminate()
Push a terminate handler on the stack.
Definition: CGCleanup.cpp:267
void pushCleanupTuple(CleanupKind Kind, std::tuple< As... > A)
Push a lazily-created cleanup on the stack. Tuple version.
Definition: EHScopeStack.h:286
@ NormalCleanup
Denotes a cleanup that should run when a scope is exited using normal control flow (falling off the e...
Definition: EHScopeStack.h:84
@ EHCleanup
Denotes a cleanup that should run when a scope is exited using exceptional control flow (a throw stat...
Definition: EHScopeStack.h:80
Definition: Format.h:4664
__PTRDIFF_TYPE__ ptrdiff_t
A signed integer type that is the result of subtracting two pointers.
#define false
Definition: stdbool.h:22
unsigned DestinationIndex
The destination index value.
Definition: EHScopeStack.h:49
llvm::BasicBlock * Destination
The ultimate destination of the branch.
Definition: EHScopeStack.h:46
llvm::BasicBlock * OptimisticBranchBlock
The block containing the terminator which needs to be modified into a switch if this fixup is resolve...
Definition: EHScopeStack.h:40
llvm::BranchInst * InitialBranch
The initial branch of the fixup.
Definition: EHScopeStack.h:52
A metaprogramming class for ensuring that a value will dominate an arbitrary position in a function.
Definition: EHScopeStack.h:65
static bool needsSaving(type value)
Definition: EHScopeStack.h:58
static type restore(CodeGenFunction &CGF, saved_type value)
Definition: EHScopeStack.h:60
static saved_type save(CodeGenFunction &CGF, type value)
Definition: EHScopeStack.h:59