1 //===-- llvm/CodeGen/GCStrategy.h - Garbage collection ----------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
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
16 // When requested, the GCStrategy will be populated with data about each
17 // function which uses it. Specifically:
20 // Garbage collection is generally only possible at certain points in code.
21 // GCStrategy can request that the collector insert such points:
23 // - At and after any call to a subroutine
24 // - Before returning from the current function
25 // - Before backwards branches (loops)
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.
31 // This information can used to emit the metadata tables which are required by
32 // the target garbage collector runtime.
34 //===----------------------------------------------------------------------===//
36 #ifndef LLVM_CODEGEN_GCSTRATEGY_H
37 #define LLVM_CODEGEN_GCSTRATEGY_H
39 #include "llvm/CodeGen/GCMetadata.h"
40 #include "llvm/CodeGen/MachineFunction.h"
41 #include "llvm/Support/Registry.h"
48 /// The GC strategy registry uses all the defaults from Registry.
50 typedef Registry<GCStrategy> GCRegistry;
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. GCStrategy objects currently must be looked up
55 /// through the GCModuleInfo analysis pass. They are owned by the analysis
56 /// pass and recreated every time that pass is invalidated.
59 friend class GCModuleInfo;
63 unsigned NeededSafePoints; ///< Bitmask of required safe points.
64 bool CustomReadBarriers; ///< Default is to insert loads.
65 bool CustomWriteBarriers; ///< Default is to insert stores.
66 bool CustomRoots; ///< Default is to pass through to backend.
67 bool CustomSafePoints; ///< Default is to use NeededSafePoints
68 ///< to find safe points.
69 bool InitRoots; ///< If set, roots are nulled during lowering.
70 bool UsesMetadata; ///< If set, backend must emit metadata tables.
75 virtual ~GCStrategy() {}
78 /// getName - The name of the GC strategy, for debugging.
80 const std::string &getName() const { return Name; }
82 /// needsSafePoitns - True if safe points of any kind are required. By
83 // default, none are recorded.
84 bool needsSafePoints() const {
85 return CustomSafePoints || NeededSafePoints != 0;
88 /// needsSafePoint(Kind) - True if the given kind of safe point is
89 // required. By default, none are recorded.
90 bool needsSafePoint(GC::PointKind Kind) const {
91 return (NeededSafePoints & 1 << Kind) != 0;
94 /// customWriteBarrier - By default, write barriers are replaced with simple
95 /// store instructions. If true, then
96 /// performCustomLowering must instead lower them.
97 bool customWriteBarrier() const { return CustomWriteBarriers; }
99 /// customReadBarrier - By default, read barriers are replaced with simple
100 /// load instructions. If true, then
101 /// performCustomLowering must instead lower them.
102 bool customReadBarrier() const { return CustomReadBarriers; }
104 /// customRoots - By default, roots are left for the code generator so it
105 /// can generate a stack map. If true, then
106 // performCustomLowering must delete them.
107 bool customRoots() const { return CustomRoots; }
109 /// customSafePoints - By default, the GC analysis will find safe
110 /// points according to NeededSafePoints. If true,
111 /// then findCustomSafePoints must create them.
112 bool customSafePoints() const { return CustomSafePoints; }
114 /// initializeRoots - If set, gcroot intrinsics should initialize their
115 // allocas to null before the first use. This is
116 // necessary for most GCs and is enabled by default.
117 bool initializeRoots() const { return InitRoots; }
119 /// usesMetadata - If set, appropriate metadata tables must be emitted by
120 /// the back-end (assembler, JIT, or otherwise).
121 bool usesMetadata() const { return UsesMetadata; }
123 /// initializeCustomLowering/performCustomLowering - If any of the actions
124 /// are set to custom, performCustomLowering must be overriden to transform
125 /// the corresponding actions to LLVM IR. initializeCustomLowering is
126 /// optional to override. These are the only GCStrategy methods through
127 /// which the LLVM IR can be modified.
128 virtual bool initializeCustomLowering(Module &F);
129 virtual bool performCustomLowering(Function &F);
130 virtual bool findCustomSafePoints(GCFunctionInfo& FI, MachineFunction& MF);