Subzero. Allocate global initializers from a dedicated arena.

src/IceDefs.h

 //===- subzero/src/IceDefs.h - Common Subzero declarations ------*- C++ -*-===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 55 matching lines @@
 class InstTarget;
 class LiveRange;
 class Liveness;
 class Operand;
 class TargetDataLowering;
 class TargetLowering;
 class Variable;
 class VariableDeclaration;
 class VariablesMetadata;
 
+/// SizeT is for holding small-ish limits like number of source operands in an
+/// instruction. It is used instead of size_t (which may be 64-bits wide) when
+/// we want to save space.
+using SizeT = uint32_t;
+
 constexpr char GlobalOffsetTable[] = "_GLOBAL_OFFSET_TABLE_";
 // makeUnique should be used when memory is expected to be allocated from the
 // heap (as opposed to allocated from some Allocator.) It is intended to be
 // used instead of new.
 //
 // The expected usage is as follows
 //
 // class MyClass {
 // public:
 //   static std::unique_ptr<MyClass> create(<ctor_args>) {
@@ skipping 46 matching lines @@
 template <typename T> using CfgVector = std::vector<T, CfgLocalAllocator<T>>;
 
 // Containers that are arena-allocated from the Cfg's allocator.
 using OperandList = CfgVector<Operand *>;
 using VarList = CfgVector<Variable *>;
 using NodeList = CfgVector<CfgNode *>;
 
 // Containers that use the default (global) allocator.
 using ConstantList = std::vector<Constant *>;
 using FunctionDeclarationList = std::vector<FunctionDeclaration *>;
-using VariableDeclarationList = std::vector<VariableDeclaration *>;
 
-/// SizeT is for holding small-ish limits like number of source operands in an
-/// instruction. It is used instead of size_t (which may be 64-bits wide) when
-/// we want to save space.
-using SizeT = uint32_t;
+/// VariableDeclarationList is a container for holding VariableDeclarations --

[Jim Stichnoth, 2016/03/14 22:21:31]

Can this go somewhere besides IceDefs.h?

[John, 2016/03/15 15:07:18]

It **should**, but because IceDefs moving it to a proper place (i.e.,
IceGlobalInits.h) requires moar changes.

I will leave this as is, in the hopes that the monstrosity IceDefs is becoming
will soon encourage/demand refactoring it (i.e., getting rid of it completely.)

[Jim Stichnoth, 2016/03/15 15:48:29]

Ick ick ick, but whatevs. :)

+/// i.e., Global Variables. It is also used to create said variables, and their
+/// initializers in an arena.
+class VariableDeclarationList {
+  VariableDeclarationList(const VariableDeclarationList &) = delete;
+  VariableDeclarationList &operator=(const VariableDeclarationList &) = delete;
+  VariableDeclarationList(VariableDeclarationList &&) = delete;
+  VariableDeclarationList &operator=(VariableDeclarationList &&) = delete;
+
+public:
+  using VariableDeclarationArray = std::vector<VariableDeclaration *>;
+
+  VariableDeclarationList() : Arena(new ArenaAllocator()) {}
+
+  ~VariableDeclarationList() { clearAndPurge(); }
+
+  template <typename T> T *allocate_initializer(SizeT Count = 1) {
+    static_assert(
+        std::is_trivially_destructible<T>::value,
+        "allocate_initializer can only allocate trivially destructible types.");
+    return Arena->Allocate<T>(Count);
+  }
+
+  template <typename T> T *allocate_variable_declaration() {
+    static_assert(!std::is_trivially_destructible<T>::value,
+                  "allocate_variable_declaration expects non-trivially "
+                  "destructible types.");
+    T *Ret = Arena->Allocate<T>();
+    Dtors.emplace_back([Ret]() { Ret->~T(); });
+    return Ret;
+  }
+
+  // This do nothing method is invoked when a global variable is created, but it
+  // will not be emitted. If we ever need to track the created variabled, having
+  // this hook is handy.
+  void willNotBeEmitted(VariableDeclaration *) {}
+
+  /// Merges Other with this, effectively resetting Other to an empty state.
+  void merge(VariableDeclarationList *Other) {
+    assert(Other != nullptr);
+    addArena(std::move(Other->Arena));
+    for (std::size_t i = 0; i < Other->MergedArenas.size(); ++i) {
+      addArena(std::move(Other->MergedArenas[i]));
+    }
+    Other->MergedArenas.clear();
+
+    Dtors.insert(Dtors.end(), Other->Dtors.begin(), Other->Dtors.end());
+    Other->Dtors.clear();
+
+    Globals.insert(Globals.end(), Other->Globals.begin(), Other->Globals.end());
+    Other->Globals.clear();
+  }
+
+  /// Destroys all GlobalVariables and initializers that this knows about
+  /// (including those merged with it), and releases memory.
+  void clearAndPurge() {
+    if (Arena == nullptr) {
+      // Arena is only null if this was merged, so we ensure there's no state
+      // being held by this.
+      assert(Dtors.empty());
+      assert(Globals.empty());
+      assert(MergedArenas.empty());
+      return;
+    }
+    // Invokes destructors in reverse creation order.
+    for (auto Dtor = Dtors.rbegin(); Dtor != Dtors.rend(); ++Dtor) {
+      (*Dtor)();
+    }
+    Dtors.clear();
+    Globals.clear();
+    MergedArenas.clear();
+    Arena->Reset();
+  }
+
+  /// Vector<VariableDeclaration *> interface.

[Jim Stichnoth, 2016/03/14 22:21:31]

I assume this comment means either "VariableDeclarationArray interface", or
"Adapt the relevant parts of the std::vector<VariableDeclaration *> interface" ?
 Otherwise it kind of looks like a typo.

[John, 2016/03/15 15:07:18]

Done.

+  /// @{
+  VariableDeclarationArray::iterator begin() { return Globals.begin(); }
+
+  VariableDeclarationArray::iterator end() { return Globals.end(); }
+
+  VariableDeclarationArray::const_iterator begin() const {
+    return Globals.begin();
+  }
+
+  VariableDeclarationArray::const_iterator end() const { return Globals.end(); }
+
+  bool empty() const { return Globals.empty(); }
+
+  VariableDeclarationArray::size_type size() const { return Globals.size(); }
+
+  VariableDeclarationArray::reference
+  at(VariableDeclarationArray::size_type Pos) {
+    return Globals.at(Pos);
+  }
+
+  void push_back(VariableDeclaration *Global) { Globals.push_back(Global); }
+
+  void reserve(VariableDeclarationArray::size_type Capacity) {
+    Globals.reserve(Capacity);
+  }
+
+  void clear() { Globals.clear(); }
+
+  VariableDeclarationArray::reference back() { return Globals.back(); }
+  /// @}
+
+private:
+  using ArenaPtr = std::unique_ptr<ArenaAllocator>;
+  using DestructorsArray = std::vector<std::function<void()>>;
+
+  void addArena(ArenaPtr NewArena) {
+    MergedArenas.emplace_back(std::move(NewArena));
+  }
+
+  ArenaPtr Arena;
+  VariableDeclarationArray Globals;
+  DestructorsArray Dtors;
+  std::vector<ArenaPtr> MergedArenas;
+};
 
 /// InstNumberT is for holding an instruction number. Instruction numbers are
 /// used for representing Variable live ranges.
 using InstNumberT = int32_t;
 
 /// A LiveBeginEndMapEntry maps a Variable::Number value to an Inst::Number
 /// value, giving the instruction number that begins or ends a variable's live
 /// range.
 using LiveBeginEndMapEntry = std::pair<SizeT, InstNumberT>;
 using LiveBeginEndMap = CfgVector<LiveBeginEndMapEntry>;
@@ skipping 127 matching lines @@
   RPE_PooledConstantReordering,
   RPE_RegAllocRandomization,
   RPE_num
 };
 
 using RelocOffsetArray = llvm::SmallVector<class RelocOffset *, 4>;
 
 } // end of namespace Ice
 
 #endif // SUBZERO_SRC_ICEDEFS_H