1 //===- llvm/CodeGen/GCStrategy.h - Garbage collection -----------*- C++ -*-===//
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
7 //===----------------------------------------------------------------------===//
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
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.
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:
24 // Garbage collection is generally only possible at certain points in code.
25 // GCStrategy can request that the collector insert such points:
27 // - At and after any call to a subroutine
28 // - Before returning from the current function
29 // - Before backwards branches (loops)
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.
35 // This information can used to emit the metadata tables which are required by
36 // the target garbage collector runtime.
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.
43 // The read and write barrier support can be used with either implementation.
45 //===----------------------------------------------------------------------===//
47 #ifndef LLVM_IR_GCSTRATEGY_H
48 #define LLVM_IR_GCSTRATEGY_H
50 #include "llvm/Support/Registry.h"
58 /// GCStrategy describes a garbage collector algorithm's code generation
59 /// requirements, and provides overridable hooks for those needs which cannot
60 /// be abstractly described. GCStrategy objects must be looked up through
61 /// the Function. The objects themselves are owned by the Context and must
65 friend class GCModuleInfo;
70 bool UseStatepoints = false; /// Uses gc.statepoints as opposed to gc.roots,
71 /// if set, NeededSafePoints and UsesMetadata
72 /// should be left at their default values.
74 bool UseRS4GC = false; /// If UseStatepoints is set, this determines whether
75 /// the RewriteStatepointsForGC pass should rewrite
76 /// this function's calls.
77 /// This should only be set if UseStatepoints is set.
79 bool NeededSafePoints = false; ///< if set, calls are inferred to be safepoints
80 bool UsesMetadata = false; ///< If set, backend must emit metadata tables.
84 virtual ~GCStrategy() = default;
86 /// Return the name of the GC strategy. This is the value of the collector
87 /// name string specified on functions which use this strategy.
88 const std::string &getName() const { return Name; }
90 /// Returns true if this strategy is expecting the use of gc.statepoints,
91 /// and false otherwise.
92 bool useStatepoints() const { return UseStatepoints; }
94 /** @name Statepoint Specific Properties */
97 /// If the type specified can be reliably distinguished, returns true for
98 /// pointers to GC managed locations and false for pointers to non-GC
99 /// managed locations. Note a GCStrategy can always return 'std::nullopt'
100 /// (i.e. an empty optional indicating it can't reliably distinguish.
101 virtual std::optional<bool> isGCManagedPointer(const Type *Ty) const {
105 /// Returns true if the RewriteStatepointsForGC pass should run on functions
107 bool useRS4GC() const {
108 assert((!UseRS4GC || useStatepoints()) &&
109 "GC strategy has useRS4GC but not useStatepoints set");
115 /// If set, appropriate metadata tables must be emitted by the back-end
116 /// (assembler, JIT, or otherwise). The default stackmap information can be
117 /// found in the StackMap section as described in the documentation.
118 bool usesMetadata() const { return UsesMetadata; }
120 /** @name GCRoot Specific Properties
121 * These properties and overrides only apply to collector strategies using
126 /// True if safe points need to be inferred on call sites
127 bool needsSafePoints() const { return NeededSafePoints; }
132 /// Subclasses of GCStrategy are made available for use during compilation by
133 /// adding them to the global GCRegistry. This can done either within the
134 /// LLVM source tree or via a loadable plugin. An example registeration
136 /// static GCRegistry::Add<CustomGC> X("custom-name",
137 /// "my custom supper fancy gc strategy");
139 /// Note that to use a custom GCMetadataPrinter, you must also
140 /// register your GCMetadataPrinter subclass with the
141 /// GCMetadataPrinterRegistery as well.
142 using GCRegistry = Registry<GCStrategy>;
144 /// Lookup the GCStrategy object associated with the given gc name.
145 std::unique_ptr<GCStrategy> getGCStrategy(const StringRef Name);
147 } // end namespace llvm
149 #endif // LLVM_IR_GCSTRATEGY_H