• Home
  • Line#
  • Scopes#
  • Navigate#
  • Raw
  • Download
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