1 //===- llvm/CodeGen/GCStrategy.h - Garbage collection -----------*- 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 // GCStrategy coordinates code generation algorithms and implements some itself 10 // in order to generate code compatible with a target code generator as 11 // specified in a function's 'gc' attribute. Algorithms are enabled by setting 12 // flags in a subclass's constructor, and some virtual methods can be 13 // overridden. 14 // 15 // GCStrategy is relevant for implementations using either gc.root or 16 // gc.statepoint based lowering strategies, but is currently focused mostly on 17 // options for gc.root. This will change over time. 18 // 19 // When requested by a subclass of GCStrategy, the gc.root implementation will 20 // populate GCModuleInfo and GCFunctionInfo with that about each Function in 21 // the Module that opts in to garbage collection. Specifically: 22 // 23 // - Safe points 24 // Garbage collection is generally only possible at certain points in code. 25 // GCStrategy can request that the collector insert such points: 26 // 27 // - At and after any call to a subroutine 28 // - Before returning from the current function 29 // - Before backwards branches (loops) 30 // 31 // - Roots 32 // When a reference to a GC-allocated object exists on the stack, it must be 33 // stored in an alloca registered with llvm.gcoot. 34 // 35 // This information can used to emit the metadata tables which are required by 36 // the target garbage collector runtime. 37 // 38 // When used with gc.statepoint, information about safepoint and roots can be 39 // found in the binary StackMap section after code generation. Safepoint 40 // placement is currently the responsibility of the frontend, though late 41 // insertion support is planned. gc.statepoint does not currently support 42 // custom stack map formats; such can be generated by parsing the standard 43 // stack map section if desired. 44 // 45 // The read and write barrier support can be used with either implementation. 46 // 47 //===----------------------------------------------------------------------===// 48 49 #ifndef LLVM_IR_GCSTRATEGY_H 50 #define LLVM_IR_GCSTRATEGY_H 51 52 #include "llvm/ADT/None.h" 53 #include "llvm/ADT/Optional.h" 54 #include "llvm/Support/Registry.h" 55 #include <string> 56 57 namespace llvm { 58 59 class Type; 60 61 /// GCStrategy describes a garbage collector algorithm's code generation 62 /// requirements, and provides overridable hooks for those needs which cannot 63 /// be abstractly described. GCStrategy objects must be looked up through 64 /// the Function. The objects themselves are owned by the Context and must 65 /// be immutable. 66 class GCStrategy { 67 private: 68 friend class GCModuleInfo; 69 70 std::string Name; 71 72 protected: 73 bool UseStatepoints = false; /// Uses gc.statepoints as opposed to gc.roots, 74 /// if set, none of the other options can be 75 /// anything but their default values. 76 77 bool NeededSafePoints = false; ///< if set, calls are inferred to be safepoints 78 bool UsesMetadata = false; ///< If set, backend must emit metadata tables. 79 80 public: 81 GCStrategy(); 82 virtual ~GCStrategy() = default; 83 84 /// Return the name of the GC strategy. This is the value of the collector 85 /// name string specified on functions which use this strategy. 86 const std::string &getName() const { return Name; } 87 88 /// Returns true if this strategy is expecting the use of gc.statepoints, 89 /// and false otherwise. 90 bool useStatepoints() const { return UseStatepoints; } 91 92 /** @name Statepoint Specific Properties */ 93 ///@{ 94 95 /// If the type specified can be reliably distinguished, returns true for 96 /// pointers to GC managed locations and false for pointers to non-GC 97 /// managed locations. Note a GCStrategy can always return 'None' (i.e. an 98 /// empty optional indicating it can't reliably distinguish. 99 virtual Optional<bool> isGCManagedPointer(const Type *Ty) const { 100 return None; 101 } 102 ///@} 103 104 /** @name GCRoot Specific Properties 105 * These properties and overrides only apply to collector strategies using 106 * GCRoot. 107 */ 108 ///@{ 109 110 /// True if safe points need to be inferred on call sites 111 bool needsSafePoints() const { return NeededSafePoints; } 112 113 /// If set, appropriate metadata tables must be emitted by the back-end 114 /// (assembler, JIT, or otherwise). For statepoint, this method is 115 /// currently unsupported. The stackmap information can be found in the 116 /// StackMap section as described in the documentation. 117 bool usesMetadata() const { return UsesMetadata; } 118 119 ///@} 120 }; 121 122 /// Subclasses of GCStrategy are made available for use during compilation by 123 /// adding them to the global GCRegistry. This can done either within the 124 /// LLVM source tree or via a loadable plugin. An example registeration 125 /// would be: 126 /// static GCRegistry::Add<CustomGC> X("custom-name", 127 /// "my custom supper fancy gc strategy"); 128 /// 129 /// Note that to use a custom GCMetadataPrinter w/gc.roots, you must also 130 /// register your GCMetadataPrinter subclass with the 131 /// GCMetadataPrinterRegistery as well. 132 using GCRegistry = Registry<GCStrategy>; 133 134 } // end namespace llvm 135 136 #endif // LLVM_IR_GCSTRATEGY_H 137
Indexes created Wed Jun 10 00:26:05 UTC 2026