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+//===- llvm/CodeGen/GCStrategy.h - Garbage collection -----------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// GCStrategy coordinates code generation algorithms and implements some itself
+// in order to generate code compatible with a target code generator as
+// specified in a function's 'gc' attribute. Algorithms are enabled by setting
+// flags in a subclass's constructor, and some virtual methods can be
+// overridden.
+//
+// GCStrategy is relevant for implementations using either gc.root or
+// gc.statepoint based lowering strategies, but is currently focused mostly on
+// options for gc.root.  This will change over time.
+//
+// When requested by a subclass of GCStrategy, the gc.root implementation will
+// populate GCModuleInfo and GCFunctionInfo with that about each Function in
+// the Module that opts in to garbage collection.  Specifically:
+//
+// - Safe points
+//   Garbage collection is generally only possible at certain points in code.
+//   GCStrategy can request that the collector insert such points:
+//
+//     - At and after any call to a subroutine
+//     - Before returning from the current function
+//     - Before backwards branches (loops)
+//
+// - Roots
+//   When a reference to a GC-allocated object exists on the stack, it must be
+//   stored in an alloca registered with llvm.gcoot.
+//
+// This information can used to emit the metadata tables which are required by
+// the target garbage collector runtime.
+//
+// When used with gc.statepoint, information about safepoint and roots can be
+// found in the binary StackMap section after code generation.  Safepoint
+// placement is currently the responsibility of the frontend, though late
+// insertion support is planned.  gc.statepoint does not currently support
+// custom stack map formats; such can be generated by parsing the standard
+// stack map section if desired.
+//
+// The read and write barrier support can be used with either implementation.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CODEGEN_GCSTRATEGY_H
+#define LLVM_CODEGEN_GCSTRATEGY_H
+
+#include "llvm/ADT/None.h"
+#include "llvm/ADT/Optional.h"
+#include "llvm/Support/Registry.h"
+#include <string>
+
+namespace llvm {
+
+class Type;
+
+/// GCStrategy describes a garbage collector algorithm's code generation
+/// requirements, and provides overridable hooks for those needs which cannot
+/// be abstractly described.  GCStrategy objects must be looked up through
+/// the Function.  The objects themselves are owned by the Context and must
+/// be immutable.
+class GCStrategy {
+private:
+  friend class GCModuleInfo;
+
+  std::string Name;
+
+protected:
+  bool UseStatepoints = false; /// Uses gc.statepoints as opposed to gc.roots,
+                               /// if set, none of the other options can be
+                               /// anything but their default values.
+
+  bool NeededSafePoints = false;    ///< if set, calls are inferred to be safepoints
+  bool UsesMetadata = false;     ///< If set, backend must emit metadata tables.
+
+public:
+  GCStrategy();
+  virtual ~GCStrategy() = default;
+
+  /// Return the name of the GC strategy.  This is the value of the collector
+  /// name string specified on functions which use this strategy.
+  const std::string &getName() const { return Name; }
+
+  /// Returns true if this strategy is expecting the use of gc.statepoints,
+  /// and false otherwise.
+  bool useStatepoints() const { return UseStatepoints; }
+
+  /** @name Statepoint Specific Properties */
+  ///@{
+
+  /// If the type specified can be reliably distinguished, returns true for
+  /// pointers to GC managed locations and false for pointers to non-GC
+  /// managed locations.  Note a GCStrategy can always return 'None' (i.e. an
+  /// empty optional indicating it can't reliably distinguish.
+  virtual Optional<bool> isGCManagedPointer(const Type *Ty) const {
+    return None;
+  }
+  ///@}
+
+  /** @name GCRoot Specific Properties
+   * These properties and overrides only apply to collector strategies using
+   * GCRoot.
+   */
+  ///@{
+
+  /// True if safe points need to be inferred on call sites
+  bool needsSafePoints() const { return NeededSafePoints; }
+
+  /// If set, appropriate metadata tables must be emitted by the back-end
+  /// (assembler, JIT, or otherwise). For statepoint, this method is
+  /// currently unsupported.  The stackmap information can be found in the
+  /// StackMap section as described in the documentation.
+  bool usesMetadata() const { return UsesMetadata; }
+
+  ///@}
+};
+
+/// Subclasses of GCStrategy are made available for use during compilation by
+/// adding them to the global GCRegistry.  This can done either within the
+/// LLVM source tree or via a loadable plugin.  An example registeration
+/// would be:
+/// static GCRegistry::Add<CustomGC> X("custom-name",
+///        "my custom supper fancy gc strategy");
+///
+/// Note that to use a custom GCMetadataPrinter w/gc.roots, you must also
+/// register your GCMetadataPrinter subclass with the
+/// GCMetadataPrinterRegistery as well.
+using GCRegistry = Registry<GCStrategy>;
+
+} // end namespace llvm
+
+#endif // LLVM_CODEGEN_GCSTRATEGY_H