text: //===-- GCMetadata.h - Garbage collector metadata ---------------*- C++ -*-===//
  //
  //                     The LLVM Compiler Infrastructure
  //
  // This file is distributed under the University of Illinois Open Source
  // License. See LICENSE.TXT for details.
  //
  //===----------------------------------------------------------------------===//
  //
  // This file declares the GCFunctionInfo and GCModuleInfo classes, which are
  // used as a communication channel from the target code generator to the target
  // garbage collectors. This interface allows code generators and garbage
  // collectors to be developed independently.
  //
  // The GCFunctionInfo class logs the data necessary to build a type accurate
  // stack map. The code generator outputs:
  //
  //   - Safe points as specified by the GCStrategy's NeededSafePoints.
  //   - Stack offsets for GC roots, as specified by calls to llvm.gcroot
  //
  // As a refinement, liveness analysis calculates the set of live roots at each
  // safe point. Liveness analysis is not presently performed by the code
  // generator, so all roots are assumed live.
  //
  // GCModuleInfo simply collects GCFunctionInfo instances for each Function as
  // they are compiled. This accretion is necessary for collectors which must emit
  // a stack map for the compilation unit as a whole. Therefore, GCFunctionInfo
  // outlives the MachineFunction from which it is derived and must not refer to
  // any code generator data structures.
  //
  //===----------------------------------------------------------------------===//
  
  #ifndef LLVM_CODEGEN_GCMETADATA_H
  #define LLVM_CODEGEN_GCMETADATA_H
  
  #include "llvm/ADT/DenseMap.h"
  #include "llvm/ADT/SmallVector.h"
  #include "llvm/ADT/StringMap.h"
  #include "llvm/CodeGen/GCStrategy.h"
  #include "llvm/IR/DebugLoc.h"
  #include "llvm/Pass.h"
  #include <memory>
  
  namespace llvm {
  class AsmPrinter;
  class Constant;
  class MCSymbol;
  
  /// GCPoint - Metadata for a collector-safe point in machine code.
  ///
  struct GCPoint {
    GC::PointKind Kind; ///< The kind of the safe point.
    MCSymbol *Label;    ///< A label.
    DebugLoc Loc;
  
    GCPoint(GC::PointKind K, MCSymbol *L, DebugLoc DL)
        : Kind(K), Label(L), Loc(DL) {}
  };
  
  /// GCRoot - Metadata for a pointer to an object managed by the garbage
  /// collector.
  struct GCRoot {
    int Num;                  ///< Usually a frame index.
    int StackOffset;          ///< Offset from the stack pointer.
    const Constant *Metadata; ///< Metadata straight from the call
                              ///< to llvm.gcroot.
  
    GCRoot(int N, const Constant *MD) : Num(N), StackOffset(-1), Metadata(MD) {}
  };
  
  /// Garbage collection metadata for a single function.  Currently, this
  /// information only applies to GCStrategies which use GCRoot.
  class GCFunctionInfo {
  public:
    typedef std::vector<GCPoint>::iterator iterator;
    typedef std::vector<GCRoot>::iterator roots_iterator;
    typedef std::vector<GCRoot>::const_iterator live_iterator;
  
  private:
    const Function &F;
    GCStrategy &S;
    uint64_t FrameSize;
    std::vector<GCRoot> Roots;
    std::vector<GCPoint> SafePoints;
  
    // FIXME: Liveness. A 2D BitVector, perhaps?
    //
    //   BitVector Liveness;
    //
    //   bool islive(int point, int root) =
    //     Liveness[point * SafePoints.size() + root]
    //
    // The bit vector is the more compact representation where >3.2% of roots
    // are live per safe point (1.5% on 64-bit hosts).
  
  public:
    GCFunctionInfo(const Function &F, GCStrategy &S);
    ~GCFunctionInfo();
  
    /// getFunction - Return the function to which this metadata applies.
    ///
    const Function &getFunction() const { return F; }
  
    /// getStrategy - Return the GC strategy for the function.
    ///
    GCStrategy &getStrategy() { return S; }
  
    /// addStackRoot - Registers a root that lives on the stack. Num is the
    ///                stack object ID for the alloca (if the code generator is
    //                 using  MachineFrameInfo).
    void addStackRoot(int Num, const Constant *Metadata) {
      Roots.push_back(GCRoot(Num, Metadata));
    }
  
    /// removeStackRoot - Removes a root.
    roots_iterator removeStackRoot(roots_iterator position) {
      return Roots.erase(position);
    }
  
    /// addSafePoint - Notes the existence of a safe point. Num is the ID of the
    /// label just prior to the safe point (if the code generator is using
    /// MachineModuleInfo).
    void addSafePoint(GC::PointKind Kind, MCSymbol *Label, DebugLoc DL) {
      SafePoints.push_back(GCPoint(Kind, Label, DL));
    }
  
    /// getFrameSize/setFrameSize - Records the function's frame size.
    ///
    uint64_t getFrameSize() const { return FrameSize; }
    void setFrameSize(uint64_t S) { FrameSize = S; }
  
    /// begin/end - Iterators for safe points.
    ///
    iterator begin() { return SafePoints.begin(); }
    iterator end() { return SafePoints.end(); }
    size_t size() const { return SafePoints.size(); }
  
    /// roots_begin/roots_end - Iterators for all roots in the function.
    ///
    roots_iterator roots_begin() { return Roots.begin(); }
    roots_iterator roots_end() { return Roots.end(); }
    size_t roots_size() const { return Roots.size(); }
  
    /// live_begin/live_end - Iterators for live roots at a given safe point.
    ///
    live_iterator live_begin(const iterator &p) { return roots_begin(); }
    live_iterator live_end(const iterator &p) { return roots_end(); }
    size_t live_size(const iterator &p) const { return roots_size(); }
  };
  
  /// An analysis pass which caches information about the entire Module.
  /// Records both the function level information used by GCRoots and a
  /// cache of the 'active' gc strategy objects for the current Module.
  class GCModuleInfo : public ImmutablePass {
    /// An owning list of all GCStrategies which have been created
    SmallVector<std::unique_ptr<GCStrategy>, 1> GCStrategyList;
    /// A helper map to speedup lookups into the above list
    StringMap<GCStrategy*> GCStrategyMap;
  
  public:
    /// Lookup the GCStrategy object associated with the given gc name.
    /// Objects are owned internally; No caller should attempt to delete the
    /// returned objects. 
    GCStrategy *getGCStrategy(const StringRef Name);
    
    /// List of per function info objects.  In theory, Each of these
    /// may be associated with a different GC.
    typedef std::vector<std::unique_ptr<GCFunctionInfo>> FuncInfoVec;
  
    FuncInfoVec::iterator funcinfo_begin() { return Functions.begin(); }
    FuncInfoVec::iterator funcinfo_end() { return Functions.end(); }
  
  private:
    /// Owning list of all GCFunctionInfos associated with this Module
    FuncInfoVec Functions;
  
    /// Non-owning map to bypass linear search when finding the GCFunctionInfo
    /// associated with a particular Function.
    typedef DenseMap<const Function *, GCFunctionInfo *> finfo_map_type;
    finfo_map_type FInfoMap;
  
  public:
    typedef SmallVector<std::unique_ptr<GCStrategy>,1>::const_iterator iterator;
  
    static char ID;
  
    GCModuleInfo();
  
    /// clear - Resets the pass. Any pass, which uses GCModuleInfo, should
    /// call it in doFinalization().
    ///
    void clear();
  
    /// begin/end - Iterators for used strategies.
    ///
    iterator begin() const { return GCStrategyList.begin(); }
    iterator end() const { return GCStrategyList.end(); }
  
    /// get - Look up function metadata.  This is currently assumed
    /// have the side effect of initializing the associated GCStrategy.  That
    /// will soon change.
    GCFunctionInfo &getFunctionInfo(const Function &F);
  };
  }
  
  #endif
  