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      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 CLANG_CODEGEN_EHSCOPESTACK_H
     17 #define CLANG_CODEGEN_EHSCOPESTACK_H
     18 
     19 #include "clang/Basic/LLVM.h"
     20 #include "llvm/ADT/SmallVector.h"
     21 #include "llvm/IR/BasicBlock.h"
     22 #include "llvm/IR/Value.h"
     23 #include "llvm/IR/Instructions.h"
     24 
     25 namespace clang {
     26 namespace CodeGen {
     27 
     28 class 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.
     36 struct 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 
     55 template <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.
     65 template <class T> struct DominatingValue : InvariantValue<T> {};
     66 
     67 template <class T, bool mightBeInstruction =
     68             llvm::is_base_of<llvm::Value, T>::value &&
     69             !llvm::is_base_of<llvm::Constant, T>::value &&
     70             !llvm::is_base_of<llvm::BasicBlock, T>::value>
     71 struct DominatingPointer;
     72 template <class T> struct DominatingPointer<T,false> : InvariantValue<T*> {};
     73 // template <class T> struct DominatingPointer<T,true> at end of file
     74 
     75 template <class T> struct DominatingValue<T*> : DominatingPointer<T> {};
     76 
     77 enum CleanupKind {
     78   EHCleanup = 0x1,
     79   NormalCleanup = 0x2,
     80   NormalAndEHCleanup = EHCleanup | NormalCleanup,
     81 
     82   InactiveCleanup = 0x4,
     83   InactiveEHCleanup = EHCleanup | InactiveCleanup,
     84   InactiveNormalCleanup = NormalCleanup | InactiveCleanup,
     85   InactiveNormalAndEHCleanup = NormalAndEHCleanup | InactiveCleanup
     86 };
     87 
     88 /// A stack of scopes which respond to exceptions, including cleanups
     89 /// and catch blocks.
     90 class EHScopeStack {
     91 public:
     92   /// A saved depth on the scope stack.  This is necessary because
     93   /// pushing scopes onto the stack invalidates iterators.
     94   class stable_iterator {
     95     friend class EHScopeStack;
     96 
     97     /// Offset from StartOfData to EndOfBuffer.
     98     ptrdiff_t Size;
     99 
    100     stable_iterator(ptrdiff_t Size) : Size(Size) {}
    101 
    102   public:
    103     static stable_iterator invalid() { return stable_iterator(-1); }
    104     stable_iterator() : Size(-1) {}
    105 
    106     bool isValid() const { return Size >= 0; }
    107 
    108     /// Returns true if this scope encloses I.
    109     /// Returns false if I is invalid.
    110     /// This scope must be valid.
    111     bool encloses(stable_iterator I) const { return Size <= I.Size; }
    112 
    113     /// Returns true if this scope strictly encloses I: that is,
    114     /// if it encloses I and is not I.
    115     /// Returns false is I is invalid.
    116     /// This scope must be valid.
    117     bool strictlyEncloses(stable_iterator I) const { return Size < I.Size; }
    118 
    119     friend bool operator==(stable_iterator A, stable_iterator B) {
    120       return A.Size == B.Size;
    121     }
    122     friend bool operator!=(stable_iterator A, stable_iterator B) {
    123       return A.Size != B.Size;
    124     }
    125   };
    126 
    127   /// Information for lazily generating a cleanup.  Subclasses must be
    128   /// POD-like: cleanups will not be destructed, and they will be
    129   /// allocated on the cleanup stack and freely copied and moved
    130   /// around.
    131   ///
    132   /// Cleanup implementations should generally be declared in an
    133   /// anonymous namespace.
    134   class Cleanup {
    135     // Anchor the construction vtable.
    136     virtual void anchor();
    137   public:
    138     /// Generation flags.
    139     class Flags {
    140       enum {
    141         F_IsForEH             = 0x1,
    142         F_IsNormalCleanupKind = 0x2,
    143         F_IsEHCleanupKind     = 0x4
    144       };
    145       unsigned flags;
    146 
    147     public:
    148       Flags() : flags(0) {}
    149 
    150       /// isForEH - true if the current emission is for an EH cleanup.
    151       bool isForEHCleanup() const { return flags & F_IsForEH; }
    152       bool isForNormalCleanup() const { return !isForEHCleanup(); }
    153       void setIsForEHCleanup() { flags |= F_IsForEH; }
    154 
    155       bool isNormalCleanupKind() const { return flags & F_IsNormalCleanupKind; }
    156       void setIsNormalCleanupKind() { flags |= F_IsNormalCleanupKind; }
    157 
    158       /// isEHCleanupKind - true if the cleanup was pushed as an EH
    159       /// cleanup.
    160       bool isEHCleanupKind() const { return flags & F_IsEHCleanupKind; }
    161       void setIsEHCleanupKind() { flags |= F_IsEHCleanupKind; }
    162     };
    163 
    164     // Provide a virtual destructor to suppress a very common warning
    165     // that unfortunately cannot be suppressed without this.  Cleanups
    166     // should not rely on this destructor ever being called.
    167     virtual ~Cleanup() {}
    168 
    169     /// Emit the cleanup.  For normal cleanups, this is run in the
    170     /// same EH context as when the cleanup was pushed, i.e. the
    171     /// immediately-enclosing context of the cleanup scope.  For
    172     /// EH cleanups, this is run in a terminate context.
    173     ///
    174     // \param flags cleanup kind.
    175     virtual void Emit(CodeGenFunction &CGF, Flags flags) = 0;
    176   };
    177 
    178   /// ConditionalCleanupN stores the saved form of its N parameters,
    179   /// then restores them and performs the cleanup.
    180   template <class T, class A0>
    181   class ConditionalCleanup1 : public Cleanup {
    182     typedef typename DominatingValue<A0>::saved_type A0_saved;
    183     A0_saved a0_saved;
    184 
    185     void Emit(CodeGenFunction &CGF, Flags flags) {
    186       A0 a0 = DominatingValue<A0>::restore(CGF, a0_saved);
    187       T(a0).Emit(CGF, flags);
    188     }
    189 
    190   public:
    191     ConditionalCleanup1(A0_saved a0)
    192       : a0_saved(a0) {}
    193   };
    194 
    195   template <class T, class A0, class A1>
    196   class ConditionalCleanup2 : public Cleanup {
    197     typedef typename DominatingValue<A0>::saved_type A0_saved;
    198     typedef typename DominatingValue<A1>::saved_type A1_saved;
    199     A0_saved a0_saved;
    200     A1_saved a1_saved;
    201 
    202     void Emit(CodeGenFunction &CGF, Flags flags) {
    203       A0 a0 = DominatingValue<A0>::restore(CGF, a0_saved);
    204       A1 a1 = DominatingValue<A1>::restore(CGF, a1_saved);
    205       T(a0, a1).Emit(CGF, flags);
    206     }
    207 
    208   public:
    209     ConditionalCleanup2(A0_saved a0, A1_saved a1)
    210       : a0_saved(a0), a1_saved(a1) {}
    211   };
    212 
    213   template <class T, class A0, class A1, class A2>
    214   class ConditionalCleanup3 : public Cleanup {
    215     typedef typename DominatingValue<A0>::saved_type A0_saved;
    216     typedef typename DominatingValue<A1>::saved_type A1_saved;
    217     typedef typename DominatingValue<A2>::saved_type A2_saved;
    218     A0_saved a0_saved;
    219     A1_saved a1_saved;
    220     A2_saved a2_saved;
    221 
    222     void Emit(CodeGenFunction &CGF, Flags flags) {
    223       A0 a0 = DominatingValue<A0>::restore(CGF, a0_saved);
    224       A1 a1 = DominatingValue<A1>::restore(CGF, a1_saved);
    225       A2 a2 = DominatingValue<A2>::restore(CGF, a2_saved);
    226       T(a0, a1, a2).Emit(CGF, flags);
    227     }
    228 
    229   public:
    230     ConditionalCleanup3(A0_saved a0, A1_saved a1, A2_saved a2)
    231       : a0_saved(a0), a1_saved(a1), a2_saved(a2) {}
    232   };
    233 
    234   template <class T, class A0, class A1, class A2, class A3>
    235   class ConditionalCleanup4 : public Cleanup {
    236     typedef typename DominatingValue<A0>::saved_type A0_saved;
    237     typedef typename DominatingValue<A1>::saved_type A1_saved;
    238     typedef typename DominatingValue<A2>::saved_type A2_saved;
    239     typedef typename DominatingValue<A3>::saved_type A3_saved;
    240     A0_saved a0_saved;
    241     A1_saved a1_saved;
    242     A2_saved a2_saved;
    243     A3_saved a3_saved;
    244 
    245     void Emit(CodeGenFunction &CGF, Flags flags) {
    246       A0 a0 = DominatingValue<A0>::restore(CGF, a0_saved);
    247       A1 a1 = DominatingValue<A1>::restore(CGF, a1_saved);
    248       A2 a2 = DominatingValue<A2>::restore(CGF, a2_saved);
    249       A3 a3 = DominatingValue<A3>::restore(CGF, a3_saved);
    250       T(a0, a1, a2, a3).Emit(CGF, flags);
    251     }
    252 
    253   public:
    254     ConditionalCleanup4(A0_saved a0, A1_saved a1, A2_saved a2, A3_saved a3)
    255       : a0_saved(a0), a1_saved(a1), a2_saved(a2), a3_saved(a3) {}
    256   };
    257 
    258 private:
    259   // The implementation for this class is in CGException.h and
    260   // CGException.cpp; the definition is here because it's used as a
    261   // member of CodeGenFunction.
    262 
    263   /// The start of the scope-stack buffer, i.e. the allocated pointer
    264   /// for the buffer.  All of these pointers are either simultaneously
    265   /// null or simultaneously valid.
    266   char *StartOfBuffer;
    267 
    268   /// The end of the buffer.
    269   char *EndOfBuffer;
    270 
    271   /// The first valid entry in the buffer.
    272   char *StartOfData;
    273 
    274   /// The innermost normal cleanup on the stack.
    275   stable_iterator InnermostNormalCleanup;
    276 
    277   /// The innermost EH scope on the stack.
    278   stable_iterator InnermostEHScope;
    279 
    280   /// The current set of branch fixups.  A branch fixup is a jump to
    281   /// an as-yet unemitted label, i.e. a label for which we don't yet
    282   /// know the EH stack depth.  Whenever we pop a cleanup, we have
    283   /// to thread all the current branch fixups through it.
    284   ///
    285   /// Fixups are recorded as the Use of the respective branch or
    286   /// switch statement.  The use points to the final destination.
    287   /// When popping out of a cleanup, these uses are threaded through
    288   /// the cleanup and adjusted to point to the new cleanup.
    289   ///
    290   /// Note that branches are allowed to jump into protected scopes
    291   /// in certain situations;  e.g. the following code is legal:
    292   ///     struct A { ~A(); }; // trivial ctor, non-trivial dtor
    293   ///     goto foo;
    294   ///     A a;
    295   ///    foo:
    296   ///     bar();
    297   SmallVector<BranchFixup, 8> BranchFixups;
    298 
    299   char *allocate(size_t Size);
    300 
    301   void *pushCleanup(CleanupKind K, size_t DataSize);
    302 
    303 public:
    304   EHScopeStack() : StartOfBuffer(0), EndOfBuffer(0), StartOfData(0),
    305                    InnermostNormalCleanup(stable_end()),
    306                    InnermostEHScope(stable_end()) {}
    307   ~EHScopeStack() { delete[] StartOfBuffer; }
    308 
    309   // Variadic templates would make this not terrible.
    310 
    311   /// Push a lazily-created cleanup on the stack.
    312   template <class T>
    313   void pushCleanup(CleanupKind Kind) {
    314     void *Buffer = pushCleanup(Kind, sizeof(T));
    315     Cleanup *Obj = new(Buffer) T();
    316     (void) Obj;
    317   }
    318 
    319   /// Push a lazily-created cleanup on the stack.
    320   template <class T, class A0>
    321   void pushCleanup(CleanupKind Kind, A0 a0) {
    322     void *Buffer = pushCleanup(Kind, sizeof(T));
    323     Cleanup *Obj = new(Buffer) T(a0);
    324     (void) Obj;
    325   }
    326 
    327   /// Push a lazily-created cleanup on the stack.
    328   template <class T, class A0, class A1>
    329   void pushCleanup(CleanupKind Kind, A0 a0, A1 a1) {
    330     void *Buffer = pushCleanup(Kind, sizeof(T));
    331     Cleanup *Obj = new(Buffer) T(a0, a1);
    332     (void) Obj;
    333   }
    334 
    335   /// Push a lazily-created cleanup on the stack.
    336   template <class T, class A0, class A1, class A2>
    337   void pushCleanup(CleanupKind Kind, A0 a0, A1 a1, A2 a2) {
    338     void *Buffer = pushCleanup(Kind, sizeof(T));
    339     Cleanup *Obj = new(Buffer) T(a0, a1, a2);
    340     (void) Obj;
    341   }
    342 
    343   /// Push a lazily-created cleanup on the stack.
    344   template <class T, class A0, class A1, class A2, class A3>
    345   void pushCleanup(CleanupKind Kind, A0 a0, A1 a1, A2 a2, A3 a3) {
    346     void *Buffer = pushCleanup(Kind, sizeof(T));
    347     Cleanup *Obj = new(Buffer) T(a0, a1, a2, a3);
    348     (void) Obj;
    349   }
    350 
    351   /// Push a lazily-created cleanup on the stack.
    352   template <class T, class A0, class A1, class A2, class A3, class A4>
    353   void pushCleanup(CleanupKind Kind, A0 a0, A1 a1, A2 a2, A3 a3, A4 a4) {
    354     void *Buffer = pushCleanup(Kind, sizeof(T));
    355     Cleanup *Obj = new(Buffer) T(a0, a1, a2, a3, a4);
    356     (void) Obj;
    357   }
    358 
    359   // Feel free to add more variants of the following:
    360 
    361   /// Push a cleanup with non-constant storage requirements on the
    362   /// stack.  The cleanup type must provide an additional static method:
    363   ///   static size_t getExtraSize(size_t);
    364   /// The argument to this method will be the value N, which will also
    365   /// be passed as the first argument to the constructor.
    366   ///
    367   /// The data stored in the extra storage must obey the same
    368   /// restrictions as normal cleanup member data.
    369   ///
    370   /// The pointer returned from this method is valid until the cleanup
    371   /// stack is modified.
    372   template <class T, class A0, class A1, class A2>
    373   T *pushCleanupWithExtra(CleanupKind Kind, size_t N, A0 a0, A1 a1, A2 a2) {
    374     void *Buffer = pushCleanup(Kind, sizeof(T) + T::getExtraSize(N));
    375     return new (Buffer) T(N, a0, a1, a2);
    376   }
    377 
    378   void pushCopyOfCleanup(CleanupKind Kind, const void *Cleanup, size_t Size) {
    379     void *Buffer = pushCleanup(Kind, Size);
    380     std::memcpy(Buffer, Cleanup, Size);
    381   }
    382 
    383   /// Pops a cleanup scope off the stack.  This is private to CGCleanup.cpp.
    384   void popCleanup();
    385 
    386   /// Push a set of catch handlers on the stack.  The catch is
    387   /// uninitialized and will need to have the given number of handlers
    388   /// set on it.
    389   class EHCatchScope *pushCatch(unsigned NumHandlers);
    390 
    391   /// Pops a catch scope off the stack.  This is private to CGException.cpp.
    392   void popCatch();
    393 
    394   /// Push an exceptions filter on the stack.
    395   class EHFilterScope *pushFilter(unsigned NumFilters);
    396 
    397   /// Pops an exceptions filter off the stack.
    398   void popFilter();
    399 
    400   /// Push a terminate handler on the stack.
    401   void pushTerminate();
    402 
    403   /// Pops a terminate handler off the stack.
    404   void popTerminate();
    405 
    406   /// Determines whether the exception-scopes stack is empty.
    407   bool empty() const { return StartOfData == EndOfBuffer; }
    408 
    409   bool requiresLandingPad() const {
    410     return InnermostEHScope != stable_end();
    411   }
    412 
    413   /// Determines whether there are any normal cleanups on the stack.
    414   bool hasNormalCleanups() const {
    415     return InnermostNormalCleanup != stable_end();
    416   }
    417 
    418   /// Returns the innermost normal cleanup on the stack, or
    419   /// stable_end() if there are no normal cleanups.
    420   stable_iterator getInnermostNormalCleanup() const {
    421     return InnermostNormalCleanup;
    422   }
    423   stable_iterator getInnermostActiveNormalCleanup() const;
    424 
    425   stable_iterator getInnermostEHScope() const {
    426     return InnermostEHScope;
    427   }
    428 
    429   stable_iterator getInnermostActiveEHScope() const;
    430 
    431   /// An unstable reference to a scope-stack depth.  Invalidated by
    432   /// pushes but not pops.
    433   class iterator;
    434 
    435   /// Returns an iterator pointing to the innermost EH scope.
    436   iterator begin() const;
    437 
    438   /// Returns an iterator pointing to the outermost EH scope.
    439   iterator end() const;
    440 
    441   /// Create a stable reference to the top of the EH stack.  The
    442   /// returned reference is valid until that scope is popped off the
    443   /// stack.
    444   stable_iterator stable_begin() const {
    445     return stable_iterator(EndOfBuffer - StartOfData);
    446   }
    447 
    448   /// Create a stable reference to the bottom of the EH stack.
    449   static stable_iterator stable_end() {
    450     return stable_iterator(0);
    451   }
    452 
    453   /// Translates an iterator into a stable_iterator.
    454   stable_iterator stabilize(iterator it) const;
    455 
    456   /// Turn a stable reference to a scope depth into a unstable pointer
    457   /// to the EH stack.
    458   iterator find(stable_iterator save) const;
    459 
    460   /// Removes the cleanup pointed to by the given stable_iterator.
    461   void removeCleanup(stable_iterator save);
    462 
    463   /// Add a branch fixup to the current cleanup scope.
    464   BranchFixup &addBranchFixup() {
    465     assert(hasNormalCleanups() && "adding fixup in scope without cleanups");
    466     BranchFixups.push_back(BranchFixup());
    467     return BranchFixups.back();
    468   }
    469 
    470   unsigned getNumBranchFixups() const { return BranchFixups.size(); }
    471   BranchFixup &getBranchFixup(unsigned I) {
    472     assert(I < getNumBranchFixups());
    473     return BranchFixups[I];
    474   }
    475 
    476   /// Pops lazily-removed fixups from the end of the list.  This
    477   /// should only be called by procedures which have just popped a
    478   /// cleanup or resolved one or more fixups.
    479   void popNullFixups();
    480 
    481   /// Clears the branch-fixups list.  This should only be called by
    482   /// ResolveAllBranchFixups.
    483   void clearFixups() { BranchFixups.clear(); }
    484 };
    485 
    486 } // namespace CodeGen
    487 } // namespace clang
    488 
    489 #endif
    490