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/Support/Registry.h" 41 #include <string> 42 43 namespace llvm { 44 45 class GCStrategy; 46 47 /// The GC strategy registry uses all the defaults from Registry. 48 /// 49 typedef Registry<GCStrategy> GCRegistry; 50 51 /// GCStrategy describes a garbage collector algorithm's code generation 52 /// requirements, and provides overridable hooks for those needs which cannot 53 /// be abstractly described. 54 class GCStrategy { 55 public: 56 typedef std::vector<GCFunctionInfo*> list_type; 57 typedef list_type::iterator iterator; 58 59 private: 60 friend class GCModuleInfo; 61 const Module *M; 62 std::string Name; 63 64 list_type Functions; 65 66 protected: 67 unsigned NeededSafePoints; //< Bitmask of required safe points. 68 bool CustomReadBarriers; //< Default is to insert loads. 69 bool CustomWriteBarriers; //< Default is to insert stores. 70 bool CustomRoots; //< Default is to pass through to backend. 71 bool InitRoots; //< If set, roots are nulled during lowering. 72 bool UsesMetadata; //< If set, backend must emit metadata tables. 73 74 public: 75 GCStrategy(); 76 77 virtual ~GCStrategy(); 78 79 80 /// getName - The name of the GC strategy, for debugging. 81 /// 82 const std::string &getName() const { return Name; } 83 84 /// getModule - The module within which the GC strategy is operating. 85 /// 86 const Module &getModule() const { return *M; } 87 88 /// needsSafePoitns - True if safe points of any kind are required. By 89 // default, none are recorded. 90 bool needsSafePoints() const { return NeededSafePoints != 0; } 91 92 /// needsSafePoint(Kind) - True if the given kind of safe point is 93 // required. By default, none are recorded. 94 bool needsSafePoint(GC::PointKind Kind) const { 95 return (NeededSafePoints & 1 << Kind) != 0; 96 } 97 98 /// customWriteBarrier - By default, write barriers are replaced with simple 99 /// store instructions. If true, then 100 /// performCustomLowering must instead lower them. 101 bool customWriteBarrier() const { return CustomWriteBarriers; } 102 103 /// customReadBarrier - By default, read barriers are replaced with simple 104 /// load instructions. If true, then 105 /// performCustomLowering must instead lower them. 106 bool customReadBarrier() const { return CustomReadBarriers; } 107 108 /// customRoots - By default, roots are left for the code generator so it 109 /// can generate a stack map. If true, then 110 // performCustomLowering must delete them. 111 bool customRoots() const { return CustomRoots; } 112 113 /// initializeRoots - If set, gcroot intrinsics should initialize their 114 // allocas to null before the first use. This is 115 // necessary for most GCs and is enabled by default. 116 bool initializeRoots() const { return InitRoots; } 117 118 /// usesMetadata - If set, appropriate metadata tables must be emitted by 119 /// the back-end (assembler, JIT, or otherwise). 120 bool usesMetadata() const { return UsesMetadata; } 121 122 /// begin/end - Iterators for function metadata. 123 /// 124 iterator begin() { return Functions.begin(); } 125 iterator end() { return Functions.end(); } 126 127 /// insertFunctionMetadata - Creates metadata for a function. 128 /// 129 GCFunctionInfo *insertFunctionInfo(const Function &F); 130 131 /// initializeCustomLowering/performCustomLowering - If any of the actions 132 /// are set to custom, performCustomLowering must be overriden to transform 133 /// the corresponding actions to LLVM IR. initializeCustomLowering is 134 /// optional to override. These are the only GCStrategy methods through 135 /// which the LLVM IR can be modified. 136 virtual bool initializeCustomLowering(Module &F); 137 virtual bool performCustomLowering(Function &F); 138 }; 139 140 } 141 142 #endif 143
