clang/lib/CodeGen/EHScopeStack.h

   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
  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             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>
  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 : 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.
  94 class EHScopeStack {
  95 public:
  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     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:
 213     ConditionalCleanup(typename DominatingValue<As>::saved_type... A)
 214         : Saved(A...) {}
 215
 216     ConditionalCleanup(SavedTuple Tuple) : Saved(std::move(Tuple)) {}
 217   };
 218
 219 private:
 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
 268 public:
 269   EHScopeStack()
 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.
 361   stable_iterator getInnermostNormalCleanup() const {
 362     return InnermostNormalCleanup;
 363   }
 364   stable_iterator getInnermostActiveNormalCleanup() const;
 365
 366   stable_iterator getInnermostEHScope() const {
 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.
 384   stable_iterator stable_begin() const {
 385     return stable_iterator(EndOfBuffer - StartOfData);
 386   }
 387
 388   /// Create a stable reference to the bottom of the EH stack.
 389   static stable_iterator stable_end() {
 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.
 401   BranchFixup &addBranchFixup() {
 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(); }
 408   BranchFixup &getBranchFixup(unsigned I) {
 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