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
19using namespace llvm;
20
21namespace {
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.
27class ErlangGC : public GCStrategy {
28public:
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.
38class OcamlGC : public GCStrategy {
39public:
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.
54class ShadowStackGC : public GCStrategy {
55public:
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.
65class StatepointGC : public GCStrategy {
66public:
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>(Val: 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.
98class CoreCLRGC : public GCStrategy {
99public:
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>(Val: 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.
122static GCRegistry::Add<ErlangGC> A("erlang",
123 "erlang-compatible garbage collector");
124static GCRegistry::Add<OcamlGC> B("ocaml", "ocaml 3.10-compatible GC");
125static GCRegistry::Add<ShadowStackGC>
126 C("shadow-stack", "Very portable GC for uncooperative code generators");
127static GCRegistry::Add<StatepointGC> D("statepoint-example",
128 "an example strategy for statepoint");
129static GCRegistry::Add<CoreCLRGC> E("coreclr", "CoreCLR-compatible GC");
130
131// Provide hook to ensure the containing library is fully loaded.
132void llvm::linkAllBuiltinGCs() {}
133