include/llvm/CodeGen/GCMetadata.h

   1 //===- GCMetadata.h - Garbage collector metadata ----------------*- 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 // This file declares the GCFunctionInfo and GCModuleInfo classes, which are
  10 // used as a communication channel from the target code generator to the target
  11 // garbage collectors. This interface allows code generators and garbage
  12 // collectors to be developed independently.
  13 //
  14 // The GCFunctionInfo class logs the data necessary to build a type accurate
  15 // stack map. The code generator outputs:
  16 //
  17 //   - Safe points as specified by the GCStrategy's NeededSafePoints.
  18 //   - Stack offsets for GC roots, as specified by calls to llvm.gcroot
  19 //
  20 // As a refinement, liveness analysis calculates the set of live roots at each
  21 // safe point. Liveness analysis is not presently performed by the code
  22 // generator, so all roots are assumed live.
  23 //
  24 // GCModuleInfo simply collects GCFunctionInfo instances for each Function as
  25 // they are compiled. This accretion is necessary for collectors which must emit
  26 // a stack map for the compilation unit as a whole. Therefore, GCFunctionInfo
  27 // outlives the MachineFunction from which it is derived and must not refer to
  28 // any code generator data structures.
  29 //
  30 //===----------------------------------------------------------------------===//
  31
  32 #ifndef LLVM_CODEGEN_GCMETADATA_H
  33 #define LLVM_CODEGEN_GCMETADATA_H
  34
  35 #include "llvm/ADT/DenseMap.h"
  36 #include "llvm/ADT/SmallVector.h"
  37 #include "llvm/ADT/StringMap.h"
  38 #include "llvm/ADT/StringRef.h"
  39 #include "llvm/CodeGen/GCStrategy.h"
  40 #include "llvm/IR/DebugLoc.h"
  41 #include "llvm/Pass.h"
  42 #include <algorithm>
  43 #include <cstddef>
  44 #include <cstdint>
  45 #include <memory>
  46 #include <vector>
  47
  48 namespace llvm {
  49
  50 class Constant;
  51 class Function;
  52 class MCSymbol;
  53
  54 /// GCPoint - Metadata for a collector-safe point in machine code.
  55 ///
  56 struct GCPoint {
  57   MCSymbol *Label;    ///< A label.
  58   DebugLoc Loc;
  59
  60   GCPoint(MCSymbol *L, DebugLoc DL)
  61       : Label(L), Loc(std::move(DL)) {}
  62 };
  63
  64 /// GCRoot - Metadata for a pointer to an object managed by the garbage
  65 /// collector.
  66 struct GCRoot {
  67   int Num;                  ///< Usually a frame index.
  68   int StackOffset = -1;     ///< Offset from the stack pointer.
  69   const Constant *Metadata; ///< Metadata straight from the call
  70                             ///< to llvm.gcroot.
  71
  72   GCRoot(int N, const Constant *MD) : Num(N), Metadata(MD) {}
  73 };
  74
  75 /// Garbage collection metadata for a single function.  Currently, this
  76 /// information only applies to GCStrategies which use GCRoot.
  77 class GCFunctionInfo {
  78 public:
  79   using iterator = std::vector<GCPoint>::iterator;
  80   using roots_iterator = std::vector<GCRoot>::iterator;
  81   using live_iterator = std::vector<GCRoot>::const_iterator;
  82
  83 private:
  84   const Function &F;
  85   GCStrategy &S;
  86   uint64_t FrameSize;
  87   std::vector<GCRoot> Roots;
  88   std::vector<GCPoint> SafePoints;
  89
  90   // FIXME: Liveness. A 2D BitVector, perhaps?
  91   //
  92   //   BitVector Liveness;
  93   //
  94   //   bool islive(int point, int root) =
  95   //     Liveness[point * SafePoints.size() + root]
  96   //
  97   // The bit vector is the more compact representation where >3.2% of roots
  98   // are live per safe point (1.5% on 64-bit hosts).
  99
 100 public:
 101   GCFunctionInfo(const Function &F, GCStrategy &S);
 102   ~GCFunctionInfo();
 103
 104   /// getFunction - Return the function to which this metadata applies.
 105   const Function &getFunction() const { return F; }
 106
 107   /// getStrategy - Return the GC strategy for the function.
 108   GCStrategy &getStrategy() { return S; }
 109
 110   /// addStackRoot - Registers a root that lives on the stack. Num is the
 111   ///                stack object ID for the alloca (if the code generator is
 112   //                 using  MachineFrameInfo).
 113   void addStackRoot(int Num, const Constant *Metadata) {
 114     Roots.push_back(GCRoot(Num, Metadata));
 115   }
 116
 117   /// removeStackRoot - Removes a root.
 118   roots_iterator removeStackRoot(roots_iterator position) {
 119     return Roots.erase(position);
 120   }
 121
 122   /// addSafePoint - Notes the existence of a safe point. Num is the ID of the
 123   /// label just prior to the safe point (if the code generator is using
 124   /// MachineModuleInfo).
 125   void addSafePoint(MCSymbol *Label, const DebugLoc &DL) {
 126     SafePoints.emplace_back(Label, DL);
 127   }
 128
 129   /// getFrameSize/setFrameSize - Records the function's frame size.
 130   uint64_t getFrameSize() const { return FrameSize; }
 131   void setFrameSize(uint64_t S) { FrameSize = S; }
 132
 133   /// begin/end - Iterators for safe points.
 134   iterator begin() { return SafePoints.begin(); }
 135   iterator end() { return SafePoints.end(); }
 136   size_t size() const { return SafePoints.size(); }
 137
 138   /// roots_begin/roots_end - Iterators for all roots in the function.
 139   roots_iterator roots_begin() { return Roots.begin(); }
 140   roots_iterator roots_end() { return Roots.end(); }
 141   size_t roots_size() const { return Roots.size(); }
 142
 143   /// live_begin/live_end - Iterators for live roots at a given safe point.
 144   live_iterator live_begin(const iterator &p) { return roots_begin(); }
 145   live_iterator live_end(const iterator &p) { return roots_end(); }
 146   size_t live_size(const iterator &p) const { return roots_size(); }
 147 };
 148
 149 /// An analysis pass which caches information about the entire Module.
 150 /// Records both the function level information used by GCRoots and a
 151 /// cache of the 'active' gc strategy objects for the current Module.
 152 class GCModuleInfo : public ImmutablePass {
 153   /// An owning list of all GCStrategies which have been created
 154   SmallVector<std::unique_ptr<GCStrategy>, 1> GCStrategyList;
 155   /// A helper map to speedup lookups into the above list
 156   StringMap<GCStrategy*> GCStrategyMap;
 157
 158 public:
 159   /// Lookup the GCStrategy object associated with the given gc name.
 160   /// Objects are owned internally; No caller should attempt to delete the
 161   /// returned objects.
 162   GCStrategy *getGCStrategy(const StringRef Name);
 163
 164   /// List of per function info objects.  In theory, Each of these
 165   /// may be associated with a different GC.
 166   using FuncInfoVec = std::vector<std::unique_ptr<GCFunctionInfo>>;
 167
 168   FuncInfoVec::iterator funcinfo_begin() { return Functions.begin(); }
 169   FuncInfoVec::iterator funcinfo_end() { return Functions.end(); }
 170
 171 private:
 172   /// Owning list of all GCFunctionInfos associated with this Module
 173   FuncInfoVec Functions;
 174
 175   /// Non-owning map to bypass linear search when finding the GCFunctionInfo
 176   /// associated with a particular Function.
 177   using finfo_map_type = DenseMap<const Function *, GCFunctionInfo *>;
 178   finfo_map_type FInfoMap;
 179
 180 public:
 181   using iterator = SmallVector<std::unique_ptr<GCStrategy>, 1>::const_iterator;
 182
 183   static char ID;
 184
 185   GCModuleInfo();
 186
 187   /// clear - Resets the pass. Any pass, which uses GCModuleInfo, should
 188   /// call it in doFinalization().
 189   ///
 190   void clear();
 191
 192   /// begin/end - Iterators for used strategies.
 193   ///
 194   iterator begin() const { return GCStrategyList.begin(); }
 195   iterator end() const { return GCStrategyList.end(); }
 196
 197   /// get - Look up function metadata.  This is currently assumed
 198   /// have the side effect of initializing the associated GCStrategy.  That
 199   /// will soon change.
 200   GCFunctionInfo &getFunctionInfo(const Function &F);
 201 };
 202
 203 } // end namespace llvm
 204
 205 #endif // LLVM_CODEGEN_GCMETADATA_H