1 //===- BuiltinGCs.cpp - Boilerplate for our built in GC types -------------===//
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 // This file contains the boilerplate required to define our various built in
10 // gc lowering strategies.
11 //
12 //===----------------------------------------------------------------------===//
13
14 #include "llvm/IR/BuiltinGCs.h"
15 #include "llvm/IR/GCStrategy.h"
16 #include "llvm/IR/DerivedTypes.h"
17 #include "llvm/Support/Casting.h"
18
19 using namespace llvm;
20
21 namespace {
22
23 /// An example GC which attempts to be compatible with Erlang/OTP garbage
24 /// collector.
25 ///
26 /// The frametable emitter is in ErlangGCPrinter.cpp.
27 class ErlangGC : public GCStrategy {
28 public:
ErlangGC()29 ErlangGC() {
30 NeededSafePoints = true;
31 UsesMetadata = true;
32 }
33 };
34
35 /// An example GC which attempts to be compatible with Objective Caml 3.10.0
36 ///
37 /// The frametable emitter is in OcamlGCPrinter.cpp.
38 class OcamlGC : public GCStrategy {
39 public:
OcamlGC()40 OcamlGC() {
41 NeededSafePoints = true;
42 UsesMetadata = true;
43 }
44 };
45
46 /// A GC strategy for uncooperative targets. This implements lowering for the
47 /// llvm.gc* intrinsics for targets that do not natively support them (which
48 /// includes the C backend). Note that the code generated is not quite as
49 /// efficient as algorithms which generate stack maps to identify roots.
50 ///
51 /// In order to support this particular transformation, all stack roots are
52 /// coallocated in the stack. This allows a fully target-independent stack map
53 /// while introducing only minor runtime overhead.
54 class ShadowStackGC : public GCStrategy {
55 public:
56 ShadowStackGC() = default;
57 };
58
59 /// A GCStrategy which serves as an example for the usage of a statepoint based
60 /// lowering strategy. This GCStrategy is intended to suitable as a default
61 /// implementation usable with any collector which can consume the standard
62 /// stackmap format generated by statepoints, uses the default addrespace to
63 /// distinguish between gc managed and non-gc managed pointers, and has
64 /// reasonable relocation semantics.
65 class StatepointGC : public GCStrategy {
66 public:
StatepointGC()67 StatepointGC() {
68 UseStatepoints = true;
69 UseRS4GC = true;
70 // These options are all gc.root specific, we specify them so that the
71 // gc.root lowering code doesn't run.
72 NeededSafePoints = false;
73 UsesMetadata = false;
74 }
75
isGCManagedPointer(const Type * Ty) const76 std::optional<bool> isGCManagedPointer(const Type *Ty) const override {
77 // Method is only valid on pointer typed values.
78 const PointerType *PT = cast<PointerType>(Ty);
79 // For the sake of this example GC, we arbitrarily pick addrspace(1) as our
80 // GC managed heap. We know that a pointer into this heap needs to be
81 // updated and that no other pointer does. Note that addrspace(1) is used
82 // only as an example, it has no special meaning, and is not reserved for
83 // GC usage.
84 return (1 == PT->getAddressSpace());
85 }
86 };
87
88 /// A GCStrategy for the CoreCLR Runtime. The strategy is similar to
89 /// Statepoint-example GC, but differs from it in certain aspects, such as:
90 /// 1) Base-pointers need not be explicitly tracked and reported for
91 /// interior pointers
92 /// 2) Uses a different format for encoding stack-maps
93 /// 3) Location of Safe-point polls: polls are only needed before loop-back
94 /// edges and before tail-calls (not needed at function-entry)
95 ///
96 /// The above differences in behavior are to be implemented in upcoming
97 /// checkins.
98 class CoreCLRGC : public GCStrategy {
99 public:
CoreCLRGC()100 CoreCLRGC() {
101 UseStatepoints = true;
102 UseRS4GC = true;
103 // These options are all gc.root specific, we specify them so that the
104 // gc.root lowering code doesn't run.
105 NeededSafePoints = false;
106 UsesMetadata = false;
107 }
108
isGCManagedPointer(const Type * Ty) const109 std::optional<bool> isGCManagedPointer(const Type *Ty) const override {
110 // Method is only valid on pointer typed values.
111 const PointerType *PT = cast<PointerType>(Ty);
112 // We pick addrspace(1) as our GC managed heap.
113 return (1 == PT->getAddressSpace());
114 }
115 };
116
117 } // end anonymous namespace
118
119 // Register all the above so that they can be found at runtime. Note that
120 // these static initializers are important since the registration list is
121 // constructed from their storage.
122 static GCRegistry::Add<ErlangGC> A("erlang",
123 "erlang-compatible garbage collector");
124 static GCRegistry::Add<OcamlGC> B("ocaml", "ocaml 3.10-compatible GC");
125 static GCRegistry::Add<ShadowStackGC>
126 C("shadow-stack", "Very portable GC for uncooperative code generators");
127 static GCRegistry::Add<StatepointGC> D("statepoint-example",
128 "an example strategy for statepoint");
129 static GCRegistry::Add<CoreCLRGC> E("coreclr", "CoreCLR-compatible GC");
130
131 // Provide hook to ensure the containing library is fully loaded.
linkAllBuiltinGCs()132 void llvm::linkAllBuiltinGCs() {}
133