clang  3.8.0
EHScopeStack.h
Go to the documentation of this file.
1 //===-- EHScopeStack.h - Stack for cleanup IR generation --------*- C++ -*-===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // These classes should be the minimum interface required for other parts of
11 // CodeGen to emit cleanups. The implementation is in CGCleanup.cpp and other
12 // implemenentation details that are not widely needed are in CGCleanup.h.
13 //
14 //===----------------------------------------------------------------------===//
15 
16 #ifndef LLVM_CLANG_LIB_CODEGEN_EHSCOPESTACK_H
17 #define LLVM_CLANG_LIB_CODEGEN_EHSCOPESTACK_H
18 
19 #include "clang/Basic/LLVM.h"
20 #include "llvm/ADT/STLExtras.h"
21 #include "llvm/ADT/SmallVector.h"
22 #include "llvm/IR/BasicBlock.h"
23 #include "llvm/IR/Instructions.h"
24 #include "llvm/IR/Value.h"
25 
26 namespace clang {
27 namespace CodeGen {
28 
29 class CodeGenFunction;
30 
31 /// A branch fixup. These are required when emitting a goto to a
32 /// label which hasn't been emitted yet. The goto is optimistically
33 /// emitted as a branch to the basic block for the label, and (if it
34 /// occurs in a scope with non-trivial cleanups) a fixup is added to
35 /// the innermost cleanup. When a (normal) cleanup is popped, any
36 /// unresolved fixups in that scope are threaded through the cleanup.
37 struct BranchFixup {
38  /// The block containing the terminator which needs to be modified
39  /// into a switch if this fixup is resolved into the current scope.
40  /// If null, LatestBranch points directly to the destination.
41  llvm::BasicBlock *OptimisticBranchBlock;
42 
43  /// The ultimate destination of the branch.
44  ///
45  /// This can be set to null to indicate that this fixup was
46  /// successfully resolved.
47  llvm::BasicBlock *Destination;
48 
49  /// The destination index value.
50  unsigned DestinationIndex;
51 
52  /// The initial branch of the fixup.
53  llvm::BranchInst *InitialBranch;
54 };
55 
56 template <class T> struct InvariantValue {
57  typedef T type;
58  typedef T saved_type;
59  static bool needsSaving(type value) { return false; }
60  static saved_type save(CodeGenFunction &CGF, type value) { return value; }
61  static type restore(CodeGenFunction &CGF, saved_type value) { return value; }
62 };
63 
64 /// A metaprogramming class for ensuring that a value will dominate an
65 /// arbitrary position in a function.
66 template <class T> struct DominatingValue : InvariantValue<T> {};
67 
68 template <class T, bool mightBeInstruction =
69  std::is_base_of<llvm::Value, T>::value &&
70  !std::is_base_of<llvm::Constant, T>::value &&
71  !std::is_base_of<llvm::BasicBlock, T>::value>
73 template <class T> struct DominatingPointer<T,false> : InvariantValue<T*> {};
74 // template <class T> struct DominatingPointer<T,true> at end of file
75 
76 template <class T> struct DominatingValue<T*> : DominatingPointer<T> {};
77 
78 enum CleanupKind : unsigned {
79  /// Denotes a cleanup that should run when a scope is exited using exceptional
80  /// control flow (a throw statement leading to stack unwinding, ).
81  EHCleanup = 0x1,
82 
83  /// Denotes a cleanup that should run when a scope is exited using normal
84  /// control flow (falling off the end of the scope, return, goto, ...).
86 
88 
93 };
94 
95 /// A stack of scopes which respond to exceptions, including cleanups
96 /// and catch blocks.
97 class EHScopeStack {
98 public:
99  /* Should switch to alignof(uint64_t) instead of 8, when EHCleanupScope can */
100  enum { ScopeStackAlignment = 8 };
101 
102  /// A saved depth on the scope stack. This is necessary because
103  /// pushing scopes onto the stack invalidates iterators.
105  friend class EHScopeStack;
106 
107  /// Offset from StartOfData to EndOfBuffer.
108  ptrdiff_t Size;
109 
110  stable_iterator(ptrdiff_t Size) : Size(Size) {}
111 
112  public:
113  static stable_iterator invalid() { return stable_iterator(-1); }
114  stable_iterator() : Size(-1) {}
115 
116  bool isValid() const { return Size >= 0; }
117 
118  /// Returns true if this scope encloses I.
119  /// Returns false if I is invalid.
120  /// This scope must be valid.
121  bool encloses(stable_iterator I) const { return Size <= I.Size; }
122 
123  /// Returns true if this scope strictly encloses I: that is,
124  /// if it encloses I and is not I.
125  /// Returns false is I is invalid.
126  /// This scope must be valid.
127  bool strictlyEncloses(stable_iterator I) const { return Size < I.Size; }
128 
130  return A.Size == B.Size;
131  }
133  return A.Size != B.Size;
134  }
135  };
136 
137  /// Information for lazily generating a cleanup. Subclasses must be
138  /// POD-like: cleanups will not be destructed, and they will be
139  /// allocated on the cleanup stack and freely copied and moved
140  /// around.
141  ///
142  /// Cleanup implementations should generally be declared in an
143  /// anonymous namespace.
144  class Cleanup {
145  // Anchor the construction vtable.
146  virtual void anchor();
147 
148  protected:
149  ~Cleanup() = default;
150 
151  public:
152  Cleanup(const Cleanup &) = default;
154  Cleanup() = default;
155 
156  /// Generation flags.
157  class Flags {
158  enum {
159  F_IsForEH = 0x1,
160  F_IsNormalCleanupKind = 0x2,
161  F_IsEHCleanupKind = 0x4
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 
182 
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.
187  ///
188  // \param flags cleanup kind.
189  virtual void Emit(CodeGenFunction &CGF, Flags flags) = 0;
190  };
191 
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;
197  SavedTuple Saved;
198 
199  template <std::size_t... Is>
200  T restore(CodeGenFunction &CGF, llvm::index_sequence<Is...>) {
201  // It's important that the restores are emitted in order. The braced init
202  // list guarentees that.
203  return T{DominatingValue<As>::restore(CGF, std::get<Is>(Saved))...};
204  }
205 
206  void Emit(CodeGenFunction &CGF, Flags flags) override {
207  restore(CGF, llvm::index_sequence_for<As...>()).Emit(CGF, flags);
208  }
209 
210  public:
212  : Saved(A...) {}
213 
214  ConditionalCleanup(SavedTuple Tuple) : Saved(std::move(Tuple)) {}
215  };
216 
217 private:
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.
221 
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.
225  char *StartOfBuffer;
226 
227  /// The end of the buffer.
228  char *EndOfBuffer;
229 
230  /// The first valid entry in the buffer.
231  char *StartOfData;
232 
233  /// The innermost normal cleanup on the stack.
234  stable_iterator InnermostNormalCleanup;
235 
236  /// The innermost EH scope on the stack.
237  stable_iterator InnermostEHScope;
238 
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.
243  ///
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.
248  ///
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
252  /// goto foo;
253  /// A a;
254  /// foo:
255  /// bar();
256  SmallVector<BranchFixup, 8> BranchFixups;
257 
258  char *allocate(size_t Size);
259  void deallocate(size_t Size);
260 
261  void *pushCleanup(CleanupKind K, size_t DataSize);
262 
263 public:
264  EHScopeStack() : StartOfBuffer(nullptr), EndOfBuffer(nullptr),
265  StartOfData(nullptr), InnermostNormalCleanup(stable_end()),
266  InnermostEHScope(stable_end()) {}
267  ~EHScopeStack() { delete[] StartOfBuffer; }
268 
269  /// Push a lazily-created cleanup on the stack.
270  template <class T, class... As> void pushCleanup(CleanupKind Kind, As... A) {
271  static_assert(llvm::AlignOf<T>::Alignment <= ScopeStackAlignment,
272  "Cleanup's alignment is too large.");
273  void *Buffer = pushCleanup(Kind, sizeof(T));
274  Cleanup *Obj = new (Buffer) T(A...);
275  (void) Obj;
276  }
277 
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(llvm::AlignOf<T>::Alignment <= ScopeStackAlignment,
282  "Cleanup's alignment is too large.");
283  void *Buffer = pushCleanup(Kind, sizeof(T));
284  Cleanup *Obj = new (Buffer) T(std::move(A));
285  (void) Obj;
286  }
287 
288  // Feel free to add more variants of the following:
289 
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.
295  ///
296  /// The data stored in the extra storage must obey the same
297  /// restrictions as normal cleanup member data.
298  ///
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(llvm::AlignOf<T>::Alignment <= 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...);
307  }
308 
309  void pushCopyOfCleanup(CleanupKind Kind, const void *Cleanup, size_t Size) {
310  void *Buffer = pushCleanup(Kind, Size);
311  std::memcpy(Buffer, Cleanup, Size);
312  }
313 
314  /// Pops a cleanup scope off the stack. This is private to CGCleanup.cpp.
315  void popCleanup();
316 
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
319  /// set on it.
320  class EHCatchScope *pushCatch(unsigned NumHandlers);
321 
322  /// Pops a catch scope off the stack. This is private to CGException.cpp.
323  void popCatch();
324 
325  /// Push an exceptions filter on the stack.
326  class EHFilterScope *pushFilter(unsigned NumFilters);
327 
328  /// Pops an exceptions filter off the stack.
329  void popFilter();
330 
331  /// Push a terminate handler on the stack.
332  void pushTerminate();
333 
334  /// Pops a terminate handler off the stack.
335  void popTerminate();
336 
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;
340 
341  /// Determines whether the exception-scopes stack is empty.
342  bool empty() const { return StartOfData == EndOfBuffer; }
343 
344  bool requiresLandingPad() const {
345  return InnermostEHScope != stable_end();
346  }
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.
356  return InnermostNormalCleanup;
357  }
358  stable_iterator getInnermostActiveNormalCleanup() const;
359 
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.
379  return stable_iterator(EndOfBuffer - StartOfData);
380  }
381 
382  /// Create a stable reference to the bottom of the EH stack.
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.
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(); }
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
void pushTerminate()
Push a terminate handler on the stack.
Definition: CGCleanup.cpp:243
iterator end() const
Returns an iterator pointing to the outermost EH scope.
Definition: CGCleanup.h:570
ConditionalCleanup(typename DominatingValue< As >::saved_type...A)
Definition: EHScopeStack.h:211
void pushCleanup(CleanupKind Kind, As...A)
Push a lazily-created cleanup on the stack.
Definition: EHScopeStack.h:270
static stable_iterator stable_end()
Create a stable reference to the bottom of the EH stack.
Definition: EHScopeStack.h:383
std::unique_ptr< llvm::MemoryBuffer > Buffer
static saved_type save(CodeGenFunction &CGF, type value)
Definition: EHScopeStack.h:60
T * pushCleanupWithExtra(CleanupKind Kind, size_t N, As...A)
Push a cleanup with non-constant storage requirements on the stack.
Definition: EHScopeStack.h:302
void pushCleanupTuple(CleanupKind Kind, std::tuple< As...> A)
Push a lazily-created cleanup on the stack. Tuple version.
Definition: EHScopeStack.h:280
A scope which attempts to handle some, possibly all, types of exceptions.
Definition: CGCleanup.h:153
stable_iterator stabilize(iterator it) const
Translates an iterator into a stable_iterator.
Definition: CGCleanup.h:597
ConditionalCleanup stores the saved form of its parameters, then restores them and performs the clean...
Definition: EHScopeStack.h:195
CodeGenFunction - This class organizes the per-function state that is used while generating LLVM code...
Denotes a cleanup that should run when a scope is exited using exceptional control flow (a throw stat...
Definition: EHScopeStack.h:81
A metaprogramming class for ensuring that a value will dominate an arbitrary position in a function...
Definition: EHScopeStack.h:66
class EHCatchScope * pushCatch(unsigned NumHandlers)
Push a set of catch handlers on the stack.
Definition: CGCleanup.cpp:235
iterator begin() const
Returns an iterator pointing to the innermost EH scope.
Definition: CGCleanup.h:566
BranchFixup & getBranchFixup(unsigned I)
Definition: EHScopeStack.h:402
Forward-declares and imports various common LLVM datatypes that clang wants to use unqualified...
A stack of scopes which respond to exceptions, including cleanups and catch blocks.
Definition: EHScopeStack.h:97
Denotes a cleanup that should run when a scope is exited using normal control flow (falling off the e...
Definition: EHScopeStack.h:85
void popFilter()
Pops an exceptions filter off the stack.
Definition: CGCleanup.cpp:226
detail::InMemoryDirectory::const_iterator I
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:590
unsigned getNumBranchFixups() const
Definition: EHScopeStack.h:401
static type restore(CodeGenFunction &CGF, saved_type value)
Definition: EHScopeStack.h:61
llvm::BranchInst * InitialBranch
The initial branch of the fixup.
Definition: EHScopeStack.h:53
bool empty() const
Determines whether the exception-scopes stack is empty.
Definition: EHScopeStack.h:342
void clearFixups()
Clears the branch-fixups list.
Definition: EHScopeStack.h:414
stable_iterator stable_begin() const
Create a stable reference to the top of the EH stack.
Definition: EHScopeStack.h:378
bool containsOnlyLifetimeMarkers(stable_iterator Old) const
Definition: CGCleanup.cpp:149
void popCleanup()
Pops a cleanup scope off the stack. This is private to CGCleanup.cpp.
Definition: CGCleanup.cpp:193
llvm::BasicBlock * OptimisticBranchBlock
The block containing the terminator which needs to be modified into a switch if this fixup is resolve...
Definition: EHScopeStack.h:41
void popCatch()
Pops a catch scope off the stack. This is private to CGException.cpp.
Definition: CGCleanup.h:574
#define false
Definition: stdbool.h:33
llvm::BasicBlock * Destination
The ultimate destination of the branch.
Definition: EHScopeStack.h:47
Kind
A saved depth on the scope stack.
Definition: EHScopeStack.h:104
static bool needsSaving(type value)
Definition: EHScopeStack.h:59
void pushCopyOfCleanup(CleanupKind Kind, const void *Cleanup, size_t Size)
Definition: EHScopeStack.h:309
unsigned DestinationIndex
The destination index value.
Definition: EHScopeStack.h:50
virtual void Emit(CodeGenFunction &CGF, Flags flags)=0
Emit the cleanup.
friend bool operator==(stable_iterator A, stable_iterator B)
Definition: EHScopeStack.h:129
__SIZE_TYPE__ size_t
Definition: stddef.h:62
Represents a template argument.
Definition: TemplateBase.h:40
class EHFilterScope * pushFilter(unsigned NumFilters)
Push an exceptions filter on the stack.
Definition: CGCleanup.cpp:218
bool encloses(stable_iterator I) const
Returns true if this scope encloses I.
Definition: EHScopeStack.h:121
BranchFixup & addBranchFixup()
Add a branch fixup to the current cleanup scope.
Definition: EHScopeStack.h:395
void popNullFixups()
Pops lazily-removed fixups from the end of the list.
Definition: CGCleanup.cpp:254
friend bool operator!=(stable_iterator A, stable_iterator B)
Definition: EHScopeStack.h:132
bool isEHCleanupKind() const
isEHCleanupKind - true if the cleanup was pushed as an EH cleanup.
Definition: EHScopeStack.h:178
__PTRDIFF_TYPE__ ptrdiff_t
Definition: stddef.h:51
stable_iterator getInnermostActiveNormalCleanup() const
Definition: CGCleanup.cpp:161
void popTerminate()
Pops a terminate handler off the stack.
Definition: CGCleanup.h:582
bool hasNormalCleanups() const
Determines whether there are any normal cleanups on the stack.
Definition: EHScopeStack.h:349
stable_iterator getInnermostEHScope() const
Definition: EHScopeStack.h:360
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:127
stable_iterator getInnermostNormalCleanup() const
Returns the innermost normal cleanup on the stack, or stable_end() if there are no normal cleanups...
Definition: EHScopeStack.h:355
An exceptions scope which filters exceptions thrown through it.
Definition: CGCleanup.h:438
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:144
bool requiresLandingPad() const
Definition: EHScopeStack.h:344