| //===- llvm/CodeGen/GCStrategy.h - Garbage collection -----------*- C++ -*-===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file is distributed under the University of Illinois Open Source |
| // License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // GCStrategy coordinates code generation algorithms and implements some itself |
| // in order to generate code compatible with a target code generator as |
| // specified in a function's 'gc' attribute. Algorithms are enabled by setting |
| // flags in a subclass's constructor, and some virtual methods can be |
| // overridden. |
| // |
| // GCStrategy is relevant for implementations using either gc.root or |
| // gc.statepoint based lowering strategies, but is currently focused mostly on |
| // options for gc.root. This will change over time. |
| // |
| // When requested by a subclass of GCStrategy, the gc.root implementation will |
| // populate GCModuleInfo and GCFunctionInfo with that about each Function in |
| // the Module that opts in to garbage collection. Specifically: |
| // |
| // - Safe points |
| // Garbage collection is generally only possible at certain points in code. |
| // GCStrategy can request that the collector insert such points: |
| // |
| // - At and after any call to a subroutine |
| // - Before returning from the current function |
| // - Before backwards branches (loops) |
| // |
| // - Roots |
| // When a reference to a GC-allocated object exists on the stack, it must be |
| // stored in an alloca registered with llvm.gcoot. |
| // |
| // This information can used to emit the metadata tables which are required by |
| // the target garbage collector runtime. |
| // |
| // When used with gc.statepoint, information about safepoint and roots can be |
| // found in the binary StackMap section after code generation. Safepoint |
| // placement is currently the responsibility of the frontend, though late |
| // insertion support is planned. gc.statepoint does not currently support |
| // custom stack map formats; such can be generated by parsing the standard |
| // stack map section if desired. |
| // |
| // The read and write barrier support can be used with either implementation. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #ifndef LLVM_CODEGEN_GCSTRATEGY_H |
| #define LLVM_CODEGEN_GCSTRATEGY_H |
| |
| #include "llvm/ADT/None.h" |
| #include "llvm/ADT/Optional.h" |
| #include "llvm/Support/Registry.h" |
| #include <string> |
| |
| namespace llvm { |
| |
| class Type; |
| |
| namespace GC { |
| |
| /// PointKind - Used to indicate whether the address of the call instruction |
| /// or the address after the call instruction is listed in the stackmap. For |
| /// most runtimes, PostCall safepoints are appropriate. |
| /// |
| enum PointKind { |
| PreCall, ///< Instr is a call instruction. |
| PostCall ///< Instr is the return address of a call. |
| }; |
| |
| } // end namespace GC |
| |
| /// GCStrategy describes a garbage collector algorithm's code generation |
| /// requirements, and provides overridable hooks for those needs which cannot |
| /// be abstractly described. GCStrategy objects must be looked up through |
| /// the Function. The objects themselves are owned by the Context and must |
| /// be immutable. |
| class GCStrategy { |
| private: |
| friend class GCModuleInfo; |
| |
| std::string Name; |
| |
| protected: |
| bool UseStatepoints = false; /// Uses gc.statepoints as opposed to gc.roots, |
| /// if set, none of the other options can be |
| /// anything but their default values. |
| |
| unsigned NeededSafePoints = 0; ///< Bitmask of required safe points. |
| bool CustomReadBarriers = false; ///< Default is to insert loads. |
| bool CustomWriteBarriers = false; ///< Default is to insert stores. |
| bool CustomRoots = false; ///< Default is to pass through to backend. |
| bool InitRoots= true; ///< If set, roots are nulled during lowering. |
| bool UsesMetadata = false; ///< If set, backend must emit metadata tables. |
| |
| public: |
| GCStrategy(); |
| virtual ~GCStrategy() = default; |
| |
| /// Return the name of the GC strategy. This is the value of the collector |
| /// name string specified on functions which use this strategy. |
| const std::string &getName() const { return Name; } |
| |
| /// By default, write barriers are replaced with simple store |
| /// instructions. If true, you must provide a custom pass to lower |
| /// calls to @llvm.gcwrite. |
| bool customWriteBarrier() const { return CustomWriteBarriers; } |
| |
| /// By default, read barriers are replaced with simple load |
| /// instructions. If true, you must provide a custom pass to lower |
| /// calls to @llvm.gcread. |
| bool customReadBarrier() const { return CustomReadBarriers; } |
| |
| /// Returns true if this strategy is expecting the use of gc.statepoints, |
| /// and false otherwise. |
| bool useStatepoints() const { return UseStatepoints; } |
| |
| /** @name Statepoint Specific Properties */ |
| ///@{ |
| |
| /// If the type specified can be reliably distinguished, returns true for |
| /// pointers to GC managed locations and false for pointers to non-GC |
| /// managed locations. Note a GCStrategy can always return 'None' (i.e. an |
| /// empty optional indicating it can't reliably distinguish. |
| virtual Optional<bool> isGCManagedPointer(const Type *Ty) const { |
| return None; |
| } |
| ///@} |
| |
| /** @name GCRoot Specific Properties |
| * These properties and overrides only apply to collector strategies using |
| * GCRoot. |
| */ |
| ///@{ |
| |
| /// True if safe points of any kind are required. By default, none are |
| /// recorded. |
| bool needsSafePoints() const { return NeededSafePoints != 0; } |
| |
| /// True if the given kind of safe point is required. By default, none are |
| /// recorded. |
| bool needsSafePoint(GC::PointKind Kind) const { |
| return (NeededSafePoints & 1 << Kind) != 0; |
| } |
| |
| /// By default, roots are left for the code generator so it can generate a |
| /// stack map. If true, you must provide a custom pass to lower |
| /// calls to @llvm.gcroot. |
| bool customRoots() const { return CustomRoots; } |
| |
| /// If set, gcroot intrinsics should initialize their allocas to null |
| /// before the first use. This is necessary for most GCs and is enabled by |
| /// default. |
| bool initializeRoots() const { return InitRoots; } |
| |
| /// If set, appropriate metadata tables must be emitted by the back-end |
| /// (assembler, JIT, or otherwise). For statepoint, this method is |
| /// currently unsupported. The stackmap information can be found in the |
| /// StackMap section as described in the documentation. |
| bool usesMetadata() const { return UsesMetadata; } |
| |
| ///@} |
| }; |
| |
| /// Subclasses of GCStrategy are made available for use during compilation by |
| /// adding them to the global GCRegistry. This can done either within the |
| /// LLVM source tree or via a loadable plugin. An example registeration |
| /// would be: |
| /// static GCRegistry::Add<CustomGC> X("custom-name", |
| /// "my custom supper fancy gc strategy"); |
| /// |
| /// Note that to use a custom GCMetadataPrinter w/gc.roots, you must also |
| /// register your GCMetadataPrinter subclass with the |
| /// GCMetadataPrinterRegistery as well. |
| using GCRegistry = Registry<GCStrategy>; |
| |
| } // end namespace llvm |
| |
| #endif // LLVM_CODEGEN_GCSTRATEGY_H |