LLVM  10.0.0svn
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. 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_CODEGEN_GCSTRATEGY_H
50 #define LLVM_CODEGEN_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.
133 
134 } // end namespace llvm
135 
136 #endif // LLVM_CODEGEN_GCSTRATEGY_H
bool UsesMetadata
If set, backend must emit metadata tables.
Definition: GCStrategy.h:78
Type
MessagePack types as defined in the standard, with the exception of Integer being divided into a sign...
Definition: MsgPackReader.h:48
This class represents lattice values for constants.
Definition: AllocatorList.h:23
amdgpu Simplify well known AMD library false FunctionCallee Value const Twine & Name
A global registry used in conjunction with static constructors to make pluggable components (like tar...
Definition: Registry.h:44
An analysis pass which caches information about the entire Module.
Definition: GCMetadata.h:152
const std::string & getName() const
Return the name of the GC strategy.
Definition: GCStrategy.h:86
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:99
bool useStatepoints() const
Returns true if this strategy is expecting the use of gc.statepoints, and false otherwise.
Definition: GCStrategy.h:90
The instances of the Type class are immutable: once they are created, they are never changed...
Definition: Type.h:45
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:77
bool usesMetadata() const
If set, appropriate metadata tables must be emitted by the back-end (assembler, JIT, or otherwise).
Definition: GCStrategy.h:117
GCStrategy describes a garbage collector algorithm&#39;s code generation requirements, and provides overridable hooks for those needs which cannot be abstractly described.
Definition: GCStrategy.h:66
virtual ~GCStrategy()=default
bool needsSafePoints() const
True if safe points need to be inferred on call sites.
Definition: GCStrategy.h:111