LLVM  16.0.0git
GCStrategy.h
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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.
42 //
43 // The read and write barrier support can be used with either implementation.
44 //
45 //===----------------------------------------------------------------------===//
46 
47 #ifndef LLVM_IR_GCSTRATEGY_H
48 #define LLVM_IR_GCSTRATEGY_H
49 
50 #include "llvm/ADT/None.h"
51 #include "llvm/ADT/Optional.h"
52 #include "llvm/Support/Registry.h"
53 #include <string>
54 
55 namespace llvm {
56 
57 class Type;
58 
59 /// GCStrategy describes a garbage collector algorithm's code generation
60 /// requirements, and provides overridable hooks for those needs which cannot
61 /// be abstractly described. GCStrategy objects must be looked up through
62 /// the Function. The objects themselves are owned by the Context and must
63 /// be immutable.
64 class GCStrategy {
65 private:
66  friend class GCModuleInfo;
67 
68  std::string Name;
69 
70 protected:
71  bool UseStatepoints = false; /// Uses gc.statepoints as opposed to gc.roots,
72  /// if set, none of the other options can be
73  /// anything but their default values.
74 
75  bool NeededSafePoints = false; ///< if set, calls are inferred to be safepoints
76  bool UsesMetadata = false; ///< If set, backend must emit metadata tables.
77 
78 public:
79  GCStrategy();
80  virtual ~GCStrategy() = default;
81 
82  /// Return the name of the GC strategy. This is the value of the collector
83  /// name string specified on functions which use this strategy.
84  const std::string &getName() const { return Name; }
85 
86  /// Returns true if this strategy is expecting the use of gc.statepoints,
87  /// and false otherwise.
88  bool useStatepoints() const { return UseStatepoints; }
89 
90  /** @name Statepoint Specific Properties */
91  ///@{
92 
93  /// If the type specified can be reliably distinguished, returns true for
94  /// pointers to GC managed locations and false for pointers to non-GC
95  /// managed locations. Note a GCStrategy can always return 'None' (i.e. an
96  /// empty optional indicating it can't reliably distinguish.
97  virtual Optional<bool> isGCManagedPointer(const Type *Ty) const {
98  return None;
99  }
100  ///@}
101 
102  /// If set, appropriate metadata tables must be emitted by the back-end
103  /// (assembler, JIT, or otherwise). The default stackmap information can be
104  /// found in the StackMap section as described in the documentation.
105  bool usesMetadata() const { return UsesMetadata; }
106 
107  /** @name GCRoot Specific Properties
108  * These properties and overrides only apply to collector strategies using
109  * GCRoot.
110  */
111  ///@{
112 
113  /// True if safe points need to be inferred on call sites
114  bool needsSafePoints() const { return NeededSafePoints; }
115 
116  ///@}
117 };
118 
119 /// Subclasses of GCStrategy are made available for use during compilation by
120 /// adding them to the global GCRegistry. This can done either within the
121 /// LLVM source tree or via a loadable plugin. An example registeration
122 /// would be:
123 /// static GCRegistry::Add<CustomGC> X("custom-name",
124 /// "my custom supper fancy gc strategy");
125 ///
126 /// Note that to use a custom GCMetadataPrinter, you must also
127 /// register your GCMetadataPrinter subclass with the
128 /// GCMetadataPrinterRegistery as well.
130 
131 /// Lookup the GCStrategy object associated with the given gc name.
132 std::unique_ptr<GCStrategy> getGCStrategy(const StringRef Name);
133 
134 } // end namespace llvm
135 
136 #endif // LLVM_IR_GCSTRATEGY_H
llvm
This is an optimization pass for GlobalISel generic memory operations.
Definition: AddressRanges.h:18
Optional.h
llvm::GCStrategy
GCStrategy describes a garbage collector algorithm's code generation requirements,...
Definition: GCStrategy.h:64
llvm::GCStrategy::UseStatepoints
bool UseStatepoints
Definition: GCStrategy.h:71
llvm::GCStrategy::getName
const std::string & getName() const
Return the name of the GC strategy.
Definition: GCStrategy.h:84
llvm::Type
The instances of the Type class are immutable: once they are created, they are never changed.
Definition: Type.h:45
llvm::Optional< bool >
llvm::GCStrategy::GCStrategy
GCStrategy()
llvm::GCStrategy::needsSafePoints
bool needsSafePoints() const
True if safe points need to be inferred on call sites.
Definition: GCStrategy.h:114
TemplateParamKind::Type
@ Type
llvm::GCStrategy::usesMetadata
bool usesMetadata() const
If set, appropriate metadata tables must be emitted by the back-end (assembler, JIT,...
Definition: GCStrategy.h:105
None.h
llvm::StringRef
StringRef - Represent a constant reference to a string, i.e.
Definition: StringRef.h:50
Registry.h
llvm::GCStrategy::isGCManagedPointer
virtual Optional< bool > isGCManagedPointer(const Type *Ty) const
If the type specified can be reliably distinguished, returns true for pointers to GC managed location...
Definition: GCStrategy.h:97
llvm::GraphProgram::Name
Name
Definition: GraphWriter.h:50
llvm::None
constexpr std::nullopt_t None
Definition: None.h:27
llvm::GCStrategy::~GCStrategy
virtual ~GCStrategy()=default
llvm::GCStrategy::NeededSafePoints
bool NeededSafePoints
Uses gc.statepoints as opposed to gc.roots, if set, none of the other options can be anything but the...
Definition: GCStrategy.h:75
llvm::Registry
A global registry used in conjunction with static constructors to make pluggable components (like tar...
Definition: Registry.h:44
llvm::GCStrategy::useStatepoints
bool useStatepoints() const
Returns true if this strategy is expecting the use of gc.statepoints, and false otherwise.
Definition: GCStrategy.h:88
llvm::getGCStrategy
std::unique_ptr< GCStrategy > getGCStrategy(const StringRef Name)
Lookup the GCStrategy object associated with the given gc name.
Definition: GCStrategy.cpp:23
llvm::GCModuleInfo
An analysis pass which caches information about the entire Module.
Definition: GCMetadata.h:152
llvm::GCStrategy::UsesMetadata
bool UsesMetadata
If set, backend must emit metadata tables.
Definition: GCStrategy.h:76