1 //===-- llvm/CodeGen/GCStrategy.h - Garbage collection ----------*- C++ -*-===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 // 10 // GCStrategy coordinates code generation algorithms and implements some itself 11 // in order to generate code compatible with a target code generator as 12 // specified in a function's 'gc' attribute. Algorithms are enabled by setting 13 // flags in a subclass's constructor, and some virtual methods can be 14 // overridden. 15 // 16 // When requested, the GCStrategy will be populated with data about each 17 // function which uses it. Specifically: 18 // 19 // - Safe points 20 // Garbage collection is generally only possible at certain points in code. 21 // GCStrategy can request that the collector insert such points: 22 // 23 // - At and after any call to a subroutine 24 // - Before returning from the current function 25 // - Before backwards branches (loops) 26 // 27 // - Roots 28 // When a reference to a GC-allocated object exists on the stack, it must be 29 // stored in an alloca registered with llvm.gcoot. 30 // 31 // This information can used to emit the metadata tables which are required by 32 // the target garbage collector runtime. 33 // 34 //===----------------------------------------------------------------------===// 35 36 #ifndef LLVM_CODEGEN_GCSTRATEGY_H 37 #define LLVM_CODEGEN_GCSTRATEGY_H 38 39 #include "llvm/CodeGen/GCMetadata.h" 40 #include "llvm/CodeGen/MachineFunction.h" 41 #include "llvm/Support/Registry.h" 42 #include <string> 43 44 namespace llvm { 45 46 class GCStrategy; 47 48 /// The GC strategy registry uses all the defaults from Registry. 49 /// 50 typedef Registry<GCStrategy> GCRegistry; 51 52 /// GCStrategy describes a garbage collector algorithm's code generation 53 /// requirements, and provides overridable hooks for those needs which cannot 54 /// be abstractly described. 55 class GCStrategy { 56 public: 57 typedef std::vector<GCFunctionInfo*> list_type; 58 typedef list_type::iterator iterator; 59 60 private: 61 friend class GCModuleInfo; 62 const Module *M; 63 std::string Name; 64 65 list_type Functions; 66 67 protected: 68 unsigned NeededSafePoints; ///< Bitmask of required safe points. 69 bool CustomReadBarriers; ///< Default is to insert loads. 70 bool CustomWriteBarriers; ///< Default is to insert stores. 71 bool CustomRoots; ///< Default is to pass through to backend. 72 bool CustomSafePoints; ///< Default is to use NeededSafePoints 73 ///< to find safe points. 74 bool InitRoots; ///< If set, roots are nulled during lowering. 75 bool UsesMetadata; ///< If set, backend must emit metadata tables. 76 77 public: 78 GCStrategy(); 79 80 virtual ~GCStrategy(); 81 82 83 /// getName - The name of the GC strategy, for debugging. 84 /// 85 const std::string &getName() const { return Name; } 86 87 /// getModule - The module within which the GC strategy is operating. 88 /// 89 const Module &getModule() const { return *M; } 90 91 /// needsSafePoitns - True if safe points of any kind are required. By 92 // default, none are recorded. 93 bool needsSafePoints() const { 94 return CustomSafePoints || NeededSafePoints != 0; 95 } 96 97 /// needsSafePoint(Kind) - True if the given kind of safe point is 98 // required. By default, none are recorded. 99 bool needsSafePoint(GC::PointKind Kind) const { 100 return (NeededSafePoints & 1 << Kind) != 0; 101 } 102 103 /// customWriteBarrier - By default, write barriers are replaced with simple 104 /// store instructions. If true, then 105 /// performCustomLowering must instead lower them. 106 bool customWriteBarrier() const { return CustomWriteBarriers; } 107 108 /// customReadBarrier - By default, read barriers are replaced with simple 109 /// load instructions. If true, then 110 /// performCustomLowering must instead lower them. 111 bool customReadBarrier() const { return CustomReadBarriers; } 112 113 /// customRoots - By default, roots are left for the code generator so it 114 /// can generate a stack map. If true, then 115 // performCustomLowering must delete them. 116 bool customRoots() const { return CustomRoots; } 117 118 /// customSafePoints - By default, the GC analysis will find safe 119 /// points according to NeededSafePoints. If true, 120 /// then findCustomSafePoints must create them. 121 bool customSafePoints() const { return CustomSafePoints; } 122 123 /// initializeRoots - If set, gcroot intrinsics should initialize their 124 // allocas to null before the first use. This is 125 // necessary for most GCs and is enabled by default. 126 bool initializeRoots() const { return InitRoots; } 127 128 /// usesMetadata - If set, appropriate metadata tables must be emitted by 129 /// the back-end (assembler, JIT, or otherwise). 130 bool usesMetadata() const { return UsesMetadata; } 131 132 /// begin/end - Iterators for function metadata. 133 /// 134 iterator begin() { return Functions.begin(); } 135 iterator end() { return Functions.end(); } 136 137 /// insertFunctionMetadata - Creates metadata for a function. 138 /// 139 GCFunctionInfo *insertFunctionInfo(const Function &F); 140 141 /// initializeCustomLowering/performCustomLowering - If any of the actions 142 /// are set to custom, performCustomLowering must be overriden to transform 143 /// the corresponding actions to LLVM IR. initializeCustomLowering is 144 /// optional to override. These are the only GCStrategy methods through 145 /// which the LLVM IR can be modified. 146 virtual bool initializeCustomLowering(Module &F); 147 virtual bool performCustomLowering(Function &F); 148 virtual bool findCustomSafePoints(GCFunctionInfo& FI, MachineFunction& MF); 149 }; 150 151 } 152 153 #endif 154
