GCStrategy.h revision 245431 
1//===-- llvm/CodeGen/GCStrategy.h - Garbage collection ----------*- C++ -*-===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// GCStrategy coordinates code generation algorithms and implements some itself
11// in order to generate code compatible with a target code generator as
12// specified in a function's 'gc' attribute. Algorithms are enabled by setting
13// flags in a subclass's constructor, and some virtual methods can be
14// overridden.
15//
16// When requested, the GCStrategy will be populated with data about each
17// function which uses it. Specifically:
18//
19// - Safe points
20//   Garbage collection is generally only possible at certain points in code.
21//   GCStrategy can request that the collector insert such points:
22//
23//     - At and after any call to a subroutine
24//     - Before returning from the current function
25//     - Before backwards branches (loops)
26//
27// - Roots
28//   When a reference to a GC-allocated object exists on the stack, it must be
29//   stored in an alloca registered with llvm.gcoot.
30//
31// This information can used to emit the metadata tables which are required by
32// the target garbage collector runtime.
33//
34//===----------------------------------------------------------------------===//
35
36#ifndef LLVM_CODEGEN_GCSTRATEGY_H
37#define LLVM_CODEGEN_GCSTRATEGY_H
38
39#include "llvm/CodeGen/GCMetadata.h"
40#include "llvm/CodeGen/MachineFunction.h"
41#include "llvm/Support/Registry.h"
42#include <string>
43
44namespace llvm {
45
46  class GCStrategy;
47
48  /// The GC strategy registry uses all the defaults from Registry.
49  ///
50  typedef Registry<GCStrategy> GCRegistry;
51
52  /// GCStrategy describes a garbage collector algorithm's code generation
53  /// requirements, and provides overridable hooks for those needs which cannot
54  /// be abstractly described.
55  class GCStrategy {
56  public:
57    typedef std::vector<GCFunctionInfo*> list_type;
58    typedef list_type::iterator iterator;
59
60  private:
61    friend class GCModuleInfo;
62    const Module *M;
63    std::string Name;
64
65    list_type Functions;
66
67  protected:
68    unsigned NeededSafePoints; ///< Bitmask of required safe points.
69    bool CustomReadBarriers;   ///< Default is to insert loads.
70    bool CustomWriteBarriers;  ///< Default is to insert stores.
71    bool CustomRoots;          ///< Default is to pass through to backend.
72    bool CustomSafePoints;     ///< Default is to use NeededSafePoints
73                               ///< to find safe points.
74    bool InitRoots;            ///< If set, roots are nulled during lowering.
75    bool UsesMetadata;         ///< If set, backend must emit metadata tables.
76
77  public:
78    GCStrategy();
79
80    virtual ~GCStrategy();
81
82
83    /// getName - The name of the GC strategy, for debugging.
84    ///
85    const std::string &getName() const { return Name; }
86
87    /// getModule - The module within which the GC strategy is operating.
88    ///
89    const Module &getModule() const { return *M; }
90
91    /// needsSafePoitns - True if safe points of any kind are required. By
92    //                    default, none are recorded.
93    bool needsSafePoints() const {
94      return CustomSafePoints || NeededSafePoints != 0;
95    }
96
97    /// needsSafePoint(Kind) - True if the given kind of safe point is
98    //                          required. By default, none are recorded.
99    bool needsSafePoint(GC::PointKind Kind) const {
100      return (NeededSafePoints & 1 << Kind) != 0;
101    }
102
103    /// customWriteBarrier - By default, write barriers are replaced with simple
104    ///                      store instructions. If true, then
105    ///                      performCustomLowering must instead lower them.
106    bool customWriteBarrier() const { return CustomWriteBarriers; }
107
108    /// customReadBarrier - By default, read barriers are replaced with simple
109    ///                     load instructions. If true, then
110    ///                     performCustomLowering must instead lower them.
111    bool customReadBarrier() const { return CustomReadBarriers; }
112
113    /// customRoots - By default, roots are left for the code generator so it
114    ///               can generate a stack map. If true, then
115    //                performCustomLowering must delete them.
116    bool customRoots() const { return CustomRoots; }
117
118    /// customSafePoints - By default, the GC analysis will find safe
119    ///                    points according to NeededSafePoints. If true,
120    ///                    then findCustomSafePoints must create them.
121    bool customSafePoints() const { return CustomSafePoints; }
122
123    /// initializeRoots - If set, gcroot intrinsics should initialize their
124    //                    allocas to null before the first use. This is
125    //                    necessary for most GCs and is enabled by default.
126    bool initializeRoots() const { return InitRoots; }
127
128    /// usesMetadata - If set, appropriate metadata tables must be emitted by
129    ///                the back-end (assembler, JIT, or otherwise).
130    bool usesMetadata() const { return UsesMetadata; }
131
132    /// begin/end - Iterators for function metadata.
133    ///
134    iterator begin() { return Functions.begin(); }
135    iterator end()   { return Functions.end();   }
136
137    /// insertFunctionMetadata - Creates metadata for a function.
138    ///
139    GCFunctionInfo *insertFunctionInfo(const Function &F);
140
141    /// initializeCustomLowering/performCustomLowering - If any of the actions
142    /// are set to custom, performCustomLowering must be overriden to transform
143    /// the corresponding actions to LLVM IR. initializeCustomLowering is
144    /// optional to override. These are the only GCStrategy methods through
145    /// which the LLVM IR can be modified.
146    virtual bool initializeCustomLowering(Module &F);
147    virtual bool performCustomLowering(Function &F);
148    virtual bool findCustomSafePoints(GCFunctionInfo& FI, MachineFunction& MF);
149  };
150
151}
152
153#endif
154