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:
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:
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:
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 
76   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:
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 
109   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.
132 void llvm::linkAllBuiltinGCs() {}
133