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
 152     // The copy and move assignment operator is defined as deleted pending
 153     // further motivation.
 154     Cleanup &operator=(const Cleanup &) = delete;
 155     Cleanup &operator=(Cleanup &&) = delete;
 156
 157     Cleanup() = default;
 158
 159     virtual bool isRedundantBeforeReturn() { return false; }
 160
 161     /// Generation flags.
 162     class Flags {
 163       enum {
 164         F_IsForEH = 0x1,
 165         F_IsNormalCleanupKind = 0x2,
 166         F_IsEHCleanupKind = 0x4,
 167         F_HasExitSwitch = 0x8,
 168       };
 169       unsigned flags = 0;
 170
 171     public:
 172       Flags() = default;
 173
 174       /// isForEH - true if the current emission is for an EH cleanup.
 175       bool isForEHCleanup() const { return flags & F_IsForEH; }
 176       bool isForNormalCleanup() const { return !isForEHCleanup(); }
 177       void setIsForEHCleanup() { flags |= F_IsForEH; }
 178
 179       bool isNormalCleanupKind() const { return flags & F_IsNormalCleanupKind; }
 180       void setIsNormalCleanupKind() { flags |= F_IsNormalCleanupKind; }
 181
 182       /// isEHCleanupKind - true if the cleanup was pushed as an EH
 183       /// cleanup.
 184       bool isEHCleanupKind() const { return flags & F_IsEHCleanupKind; }
 185       void setIsEHCleanupKind() { flags |= F_IsEHCleanupKind; }
 186
 187       bool hasExitSwitch() const { return flags & F_HasExitSwitch; }
 188       void setHasExitSwitch() { flags |= F_HasExitSwitch; }
 189     };
 190
 191     /// Emit the cleanup.  For normal cleanups, this is run in the
 192     /// same EH context as when the cleanup was pushed, i.e. the
 193     /// immediately-enclosing context of the cleanup scope.  For
 194     /// EH cleanups, this is run in a terminate context.
 195     ///
 196     // \param flags cleanup kind.
 197     virtual void Emit(CodeGenFunction &CGF, Flags flags) = 0;
 198   };
 199
 200   /// ConditionalCleanup stores the saved form of its parameters,
 201   /// then restores them and performs the cleanup.
 202   template <class T, class... As>
 203   class ConditionalCleanup final : public Cleanup {
 204     typedef std::tuple<typename DominatingValue<As>::saved_type...> SavedTuple;
 205     SavedTuple Saved;
 206
 207     template <std::size_t... Is>
 208     T restore(CodeGenFunction &CGF, std::index_sequence<Is...>) {
 209       // It's important that the restores are emitted in order. The braced init
 210       // list guarantees that.
 211       return T{DominatingValue<As>::restore(CGF, std::get<Is>(Saved))...};
 212     }
 213
 214     void Emit(CodeGenFunction &CGF, Flags flags) override {
 215       restore(CGF, std::index_sequence_for<As...>()).Emit(CGF, flags);
 216     }
 217
 218   public:
 219     ConditionalCleanup(typename DominatingValue<As>::saved_type... A)
 220         : Saved(A...) {}
 221
 222     ConditionalCleanup(SavedTuple Tuple) : Saved(std::move(Tuple)) {}
 223   };
 224
 225 private:
 226   // The implementation for this class is in CGException.h and
 227   // CGException.cpp; the definition is here because it's used as a
 228   // member of CodeGenFunction.
 229
 230   /// The start of the scope-stack buffer, i.e. the allocated pointer
 231   /// for the buffer.  All of these pointers are either simultaneously
 232   /// null or simultaneously valid.
 233   char *StartOfBuffer;
 234
 235   /// The end of the buffer.
 236   char *EndOfBuffer;
 237
 238   /// The first valid entry in the buffer.
 239   char *StartOfData;
 240
 241   /// The innermost normal cleanup on the stack.
 242   stable_iterator InnermostNormalCleanup;
 243
 244   /// The innermost EH scope on the stack.
 245   stable_iterator InnermostEHScope;
 246
 247   /// The CGF this Stack belong to
 248   CodeGenFunction* CGF;
 249
 250   /// The current set of branch fixups.  A branch fixup is a jump to
 251   /// an as-yet unemitted label, i.e. a label for which we don't yet
 252   /// know the EH stack depth.  Whenever we pop a cleanup, we have
 253   /// to thread all the current branch fixups through it.
 254   ///
 255   /// Fixups are recorded as the Use of the respective branch or
 256   /// switch statement.  The use points to the final destination.
 257   /// When popping out of a cleanup, these uses are threaded through
 258   /// the cleanup and adjusted to point to the new cleanup.
 259   ///
 260   /// Note that branches are allowed to jump into protected scopes
 261   /// in certain situations;  e.g. the following code is legal:
 262   ///     struct A { ~A(); }; // trivial ctor, non-trivial dtor
 263   ///     goto foo;
 264   ///     A a;
 265   ///    foo:
 266   ///     bar();
 267   SmallVector<BranchFixup, 8> BranchFixups;
 268
 269   char *allocate(size_t Size);
 270   void deallocate(size_t Size);
 271
 272   void *pushCleanup(CleanupKind K, size_t DataSize);
 273
 274 public:
 275   EHScopeStack()
 276     : StartOfBuffer(nullptr), EndOfBuffer(nullptr), StartOfData(nullptr),
 277       InnermostNormalCleanup(stable_end()), InnermostEHScope(stable_end()),
 278       CGF(nullptr) {}
 279   ~EHScopeStack() { delete[] StartOfBuffer; }
 280
 281   EHScopeStack(const EHScopeStack &) = delete;
 282   EHScopeStack &operator=(const EHScopeStack &) = delete;
 283
 284   /// Push a lazily-created cleanup on the stack.
 285   template <class T, class... As> void pushCleanup(CleanupKind Kind, As... A) {
 286     static_assert(alignof(T) <= ScopeStackAlignment,
 287                   "Cleanup's alignment is too large.");
 288     void *Buffer = pushCleanup(Kind, sizeof(T));
 289     Cleanup *Obj = new (Buffer) T(A...);
 290     (void) Obj;
 291   }
 292
 293   /// Push a lazily-created cleanup on the stack. Tuple version.
 294   template <class T, class... As>
 295   void pushCleanupTuple(CleanupKind Kind, std::tuple<As...> A) {
 296     static_assert(alignof(T) <= ScopeStackAlignment,
 297                   "Cleanup's alignment is too large.");
 298     void *Buffer = pushCleanup(Kind, sizeof(T));
 299     Cleanup *Obj = new (Buffer) T(std::move(A));
 300     (void) Obj;
 301   }
 302
 303   // Feel free to add more variants of the following:
 304
 305   /// Push a cleanup with non-constant storage requirements on the
 306   /// stack.  The cleanup type must provide an additional static method:
 307   ///   static size_t getExtraSize(size_t);
 308   /// The argument to this method will be the value N, which will also
 309   /// be passed as the first argument to the constructor.
 310   ///
 311   /// The data stored in the extra storage must obey the same
 312   /// restrictions as normal cleanup member data.
 313   ///
 314   /// The pointer returned from this method is valid until the cleanup
 315   /// stack is modified.
 316   template <class T, class... As>
 317   T *pushCleanupWithExtra(CleanupKind Kind, size_t N, As... A) {
 318     static_assert(alignof(T) <= ScopeStackAlignment,
 319                   "Cleanup's alignment is too large.");
 320     void *Buffer = pushCleanup(Kind, sizeof(T) + T::getExtraSize(N));
 321     return new (Buffer) T(N, A...);
 322   }
 323
 324   void pushCopyOfCleanup(CleanupKind Kind, const void *Cleanup, size_t Size) {
 325     void *Buffer = pushCleanup(Kind, Size);
 326     std::memcpy(Buffer, Cleanup, Size);
 327   }
 328
 329   void setCGF(CodeGenFunction *inCGF) { CGF = inCGF; }
 330
 331   /// Pops a cleanup scope off the stack.  This is private to CGCleanup.cpp.
 332   void popCleanup();
 333
 334   /// Push a set of catch handlers on the stack.  The catch is
 335   /// uninitialized and will need to have the given number of handlers
 336   /// set on it.
 337   class EHCatchScope *pushCatch(unsigned NumHandlers);
 338
 339   /// Pops a catch scope off the stack.  This is private to CGException.cpp.
 340   void popCatch();
 341
 342   /// Push an exceptions filter on the stack.
 343   class EHFilterScope *pushFilter(unsigned NumFilters);
 344
 345   /// Pops an exceptions filter off the stack.
 346   void popFilter();
 347
 348   /// Push a terminate handler on the stack.
 349   void pushTerminate();
 350
 351   /// Pops a terminate handler off the stack.
 352   void popTerminate();
 353
 354   // Returns true iff the current scope is either empty or contains only
 355   // lifetime markers, i.e. no real cleanup code
 356   bool containsOnlyLifetimeMarkers(stable_iterator Old) const;
 357
 358   /// Determines whether the exception-scopes stack is empty.
 359   bool empty() const { return StartOfData == EndOfBuffer; }
 360
 361   bool requiresLandingPad() const;
 362
 363   /// Determines whether there are any normal cleanups on the stack.
 364   bool hasNormalCleanups() const {
 365     return InnermostNormalCleanup != stable_end();
 366   }
 367
 368   /// Returns the innermost normal cleanup on the stack, or
 369   /// stable_end() if there are no normal cleanups.
 370   stable_iterator getInnermostNormalCleanup() const {
 371     return InnermostNormalCleanup;
 372   }
 373   stable_iterator getInnermostActiveNormalCleanup() const;
 374
 375   stable_iterator getInnermostEHScope() const {
 376     return InnermostEHScope;
 377   }
 378
 379
 380   /// An unstable reference to a scope-stack depth.  Invalidated by
 381   /// pushes but not pops.
 382   class iterator;
 383
 384   /// Returns an iterator pointing to the innermost EH scope.
 385   iterator begin() const;
 386
 387   /// Returns an iterator pointing to the outermost EH scope.
 388   iterator end() const;
 389
 390   /// Create a stable reference to the top of the EH stack.  The
 391   /// returned reference is valid until that scope is popped off the
 392   /// stack.
 393   stable_iterator stable_begin() const {
 394     return stable_iterator(EndOfBuffer - StartOfData);
 395   }
 396
 397   /// Create a stable reference to the bottom of the EH stack.
 398   static stable_iterator stable_end() {
 399     return stable_iterator(0);
 400   }
 401
 402   /// Translates an iterator into a stable_iterator.
 403   stable_iterator stabilize(iterator it) const;
 404
 405   /// Turn a stable reference to a scope depth into a unstable pointer
 406   /// to the EH stack.
 407   iterator find(stable_iterator save) const;
 408
 409   /// Add a branch fixup to the current cleanup scope.
 410   BranchFixup &addBranchFixup() {
 411     assert(hasNormalCleanups() && "adding fixup in scope without cleanups");
 412     BranchFixups.push_back(BranchFixup());
 413     return BranchFixups.back();
 414   }
 415
 416   unsigned getNumBranchFixups() const { return BranchFixups.size(); }
 417   BranchFixup &getBranchFixup(unsigned I) {
 418     assert(I < getNumBranchFixups());
 419     return BranchFixups[I];
 420   }
 421
 422   /// Pops lazily-removed fixups from the end of the list.  This
 423   /// should only be called by procedures which have just popped a
 424   /// cleanup or resolved one or more fixups.
 425   void popNullFixups();
 426
 427   /// Clears the branch-fixups list.  This should only be called by
 428   /// ResolveAllBranchFixups.
 429   void clearFixups() { BranchFixups.clear(); }
 430 };
 431
 432 } // namespace CodeGen
 433 } // namespace clang
 434
 435 #endif