llvm/lib/IR/BuiltinGCs.cpp

   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() {}