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  InactiveCleanup = 0x4,
89  InactiveEHCleanup = EHCleanup | InactiveCleanup,
90  InactiveNormalCleanup = NormalCleanup | InactiveCleanup,
91  InactiveNormalAndEHCleanup = NormalAndEHCleanup | InactiveCleanup,
92
93  LifetimeMarker = 0x8,
94  NormalEHLifetimeMarker = LifetimeMarker | NormalAndEHCleanup,
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    Cleanup() = default;
157
158    /// Generation flags.
159    class Flags {
160      enum {
161        F_IsForEH             = 0x1,
162        F_IsNormalCleanupKind = 0x2,
163        F_IsEHCleanupKind     = 0x4
164      };
165      unsigned flags;
166
167    public:
168      Flags() : flags(0) {}
169
170      /// isForEH - true if the current emission is for an EH cleanup.
171      bool isForEHCleanup() const { return flags & F_IsForEH; }
172      bool isForNormalCleanup() const { return !isForEHCleanup(); }
173      void setIsForEHCleanup() { flags |= F_IsForEH; }
174
175      bool isNormalCleanupKind() const { return flags & F_IsNormalCleanupKind; }
176      void setIsNormalCleanupKind() { flags |= F_IsNormalCleanupKind; }
177
178      /// isEHCleanupKind - true if the cleanup was pushed as an EH
179      /// cleanup.
180      bool isEHCleanupKind() const { return flags & F_IsEHCleanupKind; }
181      void setIsEHCleanupKind() { flags |= F_IsEHCleanupKind; }
182    };
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