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 //===- GCMetadata.h - Garbage collector metadata ----------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 // 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/ADT/StringRef.h"
 #include "llvm/IR/DebugLoc.h"
 #include "llvm/IR/GCStrategy.h"
 #include "llvm/IR/PassManager.h"
 #include "llvm/Pass.h"
 #include <algorithm>
 #include <cstddef>
 #include <cstdint>
 #include <memory>
 #include <vector>
 
 namespace llvm {
 
 class Constant;
 class Function;
 class MCSymbol;
 
 /// GCPoint - Metadata for a collector-safe point in machine code.
 ///
 struct GCPoint {
   MCSymbol *Label;    ///< A label.
   DebugLoc Loc;
 
   GCPoint(MCSymbol *L, DebugLoc DL)
       : Label(L), Loc(std::move(DL)) {}
 };
 
 /// GCRoot - Metadata for a pointer to an object managed by the garbage
 /// collector.
 struct GCRoot {
   int Num;                  ///< Usually a frame index.
   int StackOffset = -1;     ///< Offset from the stack pointer.
   const Constant *Metadata; ///< Metadata straight from the call
                             ///< to llvm.gcroot.
 
   GCRoot(int N, const Constant *MD) : Num(N), Metadata(MD) {}
 };
 
 /// Garbage collection metadata for a single function.  Currently, this
 /// information only applies to GCStrategies which use GCRoot.
 class GCFunctionInfo {
 public:
   using iterator = std::vector<GCPoint>::iterator;
   using roots_iterator = std::vector<GCRoot>::iterator;
   using live_iterator = std::vector<GCRoot>::const_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();
 
   /// Handle invalidation explicitly.
   bool invalidate(Function &F, const PreservedAnalyses &PA,
                   FunctionAnalysisManager::Invalidator &Inv);
 
   /// 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(MCSymbol *Label, const DebugLoc &DL) {
     SafePoints.emplace_back(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(); }
 };
 
 struct GCStrategyMap {
   StringMap<std::unique_ptr<GCStrategy>> StrategyMap;
 
   GCStrategyMap() = default;
   GCStrategyMap(GCStrategyMap &&) = default;
 
   /// Handle invalidation explicitly.
   bool invalidate(Module &M, const PreservedAnalyses &PA,
                   ModuleAnalysisManager::Invalidator &Inv);
 };
 
 /// An analysis pass which caches information about the entire Module.
 /// Records a cache of the 'active' gc strategy objects for the current Module.
 class CollectorMetadataAnalysis
     : public AnalysisInfoMixin<CollectorMetadataAnalysis> {
   friend struct AnalysisInfoMixin<CollectorMetadataAnalysis>;
   static AnalysisKey Key;
 
 public:
   using Result = GCStrategyMap;
   Result run(Module &M, ModuleAnalysisManager &MAM);
 };
 
 /// An analysis pass which caches information about the Function.
 /// Records the function level information used by GCRoots.
 /// This pass depends on `CollectorMetadataAnalysis`.
 class GCFunctionAnalysis : public AnalysisInfoMixin<GCFunctionAnalysis> {
   friend struct AnalysisInfoMixin<GCFunctionAnalysis>;
   static AnalysisKey Key;
 
 public:
   using Result = GCFunctionInfo;
   Result run(Function &F, FunctionAnalysisManager &FAM);
 };
 
 /// LowerIntrinsics - This pass rewrites calls to the llvm.gcread or
 /// llvm.gcwrite intrinsics, replacing them with simple loads and stores as
 /// directed by the GCStrategy. It also performs automatic root initialization
 /// and custom intrinsic lowering.
 ///
 /// This pass requires `CollectorMetadataAnalysis`.
 class GCLoweringPass : public PassInfoMixin<GCLoweringPass> {
 public:
   PreservedAnalyses run(Function &F, FunctionAnalysisManager &FAM);
 };
 
 /// 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.
   using FuncInfoVec = std::vector<std::unique_ptr<GCFunctionInfo>>;
 
   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.
   using finfo_map_type = DenseMap<const Function *, GCFunctionInfo *>;
   finfo_map_type FInfoMap;
 
 public:
   using iterator = SmallVector<std::unique_ptr<GCStrategy>, 1>::const_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);
 };
 
 } // end namespace llvm
 
 #endif // LLVM_CODEGEN_GCMETADATA_H

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