1 //===-- BuiltinGCs.cpp - Boilerplate for our built in GC types --*- 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 // This file contains the boilerplate required to define our various built in
11 // gc lowering strategies.
12 //
13 //===----------------------------------------------------------------------===//
14
15 #include "llvm/CodeGen/GCs.h"
16 #include "llvm/CodeGen/GCStrategy.h"
17
18 using namespace llvm;
19
20 namespace {
21
22 /// An example GC which attempts to be compatibile with Erlang/OTP garbage
23 /// collector.
24 ///
25 /// The frametable emitter is in ErlangGCPrinter.cpp.
26 class ErlangGC : public GCStrategy {
27 public:
ErlangGC()28 ErlangGC() {
29 InitRoots = false;
30 NeededSafePoints = 1 << GC::PostCall;
31 UsesMetadata = true;
32 CustomRoots = false;
33 }
34 };
35
36 /// An example GC which attempts to be compatible with Objective Caml 3.10.0
37 ///
38 /// The frametable emitter is in OcamlGCPrinter.cpp.
39 class OcamlGC : public GCStrategy {
40 public:
OcamlGC()41 OcamlGC() {
42 NeededSafePoints = 1 << GC::PostCall;
43 UsesMetadata = true;
44 }
45 };
46
47 /// A GC strategy for uncooperative targets. This implements lowering for the
48 /// llvm.gc* intrinsics for targets that do not natively support them (which
49 /// includes the C backend). Note that the code generated is not quite as
50 /// efficient as algorithms which generate stack maps to identify roots.
51 ///
52 /// In order to support this particular transformation, all stack roots are
53 /// coallocated in the stack. This allows a fully target-independent stack map
54 /// while introducing only minor runtime overhead.
55 class ShadowStackGC : public GCStrategy {
56 public:
ShadowStackGC()57 ShadowStackGC() {
58 InitRoots = true;
59 CustomRoots = true;
60 }
61 };
62
63 /// A GCStrategy which serves as an example for the usage of a statepoint based
64 /// lowering strategy. This GCStrategy is intended to suitable as a default
65 /// implementation usable with any collector which can consume the standard
66 /// stackmap format generated by statepoints, uses the default addrespace to
67 /// distinguish between gc managed and non-gc managed pointers, and has
68 /// reasonable relocation semantics.
69 class StatepointGC : public GCStrategy {
70 public:
StatepointGC()71 StatepointGC() {
72 UseStatepoints = true;
73 // These options are all gc.root specific, we specify them so that the
74 // gc.root lowering code doesn't run.
75 InitRoots = false;
76 NeededSafePoints = 0;
77 UsesMetadata = false;
78 CustomRoots = false;
79 }
isGCManagedPointer(const Type * Ty) const80 Optional<bool> isGCManagedPointer(const Type *Ty) const override {
81 // Method is only valid on pointer typed values.
82 const PointerType *PT = cast<PointerType>(Ty);
83 // For the sake of this example GC, we arbitrarily pick addrspace(1) as our
84 // GC managed heap. We know that a pointer into this heap needs to be
85 // updated and that no other pointer does. Note that addrspace(1) is used
86 // only as an example, it has no special meaning, and is not reserved for
87 // GC usage.
88 return (1 == PT->getAddressSpace());
89 }
90 };
91
92 /// A GCStrategy for the CoreCLR Runtime. The strategy is similar to
93 /// Statepoint-example GC, but differs from it in certain aspects, such as:
94 /// 1) Base-pointers need not be explicitly tracked and reported for
95 /// interior pointers
96 /// 2) Uses a different format for encoding stack-maps
97 /// 3) Location of Safe-point polls: polls are only needed before loop-back
98 /// edges and before tail-calls (not needed at function-entry)
99 ///
100 /// The above differences in behavior are to be implemented in upcoming
101 /// checkins.
102 class CoreCLRGC : public GCStrategy {
103 public:
CoreCLRGC()104 CoreCLRGC() {
105 UseStatepoints = true;
106 // These options are all gc.root specific, we specify them so that the
107 // gc.root lowering code doesn't run.
108 InitRoots = false;
109 NeededSafePoints = 0;
110 UsesMetadata = false;
111 CustomRoots = false;
112 }
isGCManagedPointer(const Type * Ty) const113 Optional<bool> isGCManagedPointer(const Type *Ty) const override {
114 // Method is only valid on pointer typed values.
115 const PointerType *PT = cast<PointerType>(Ty);
116 // We pick addrspace(1) as our GC managed heap.
117 return (1 == PT->getAddressSpace());
118 }
119 };
120 }
121
122 // Register all the above so that they can be found at runtime. Note that
123 // these static initializers are important since the registration list is
124 // constructed from their storage.
125 static GCRegistry::Add<ErlangGC> A("erlang",
126 "erlang-compatible garbage collector");
127 static GCRegistry::Add<OcamlGC> B("ocaml", "ocaml 3.10-compatible GC");
128 static GCRegistry::Add<ShadowStackGC>
129 C("shadow-stack", "Very portable GC for uncooperative code generators");
130 static GCRegistry::Add<StatepointGC> D("statepoint-example",
131 "an example strategy for statepoint");
132 static GCRegistry::Add<CoreCLRGC> E("coreclr", "CoreCLR-compatible GC");
133
134 // Provide hooks to ensure the containing library is fully loaded.
linkErlangGC()135 void llvm::linkErlangGC() {}
linkOcamlGC()136 void llvm::linkOcamlGC() {}
linkShadowStackGC()137 void llvm::linkShadowStackGC() {}
linkStatepointExampleGC()138 void llvm::linkStatepointExampleGC() {}
linkCoreCLRGC()139 void llvm::linkCoreCLRGC() {}
140