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+//===- llvm/CodeGen/GCStrategy.h - Garbage collection -----------*- C++ -*-===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// 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;
+
+namespace GC {
+
+/// PointKind - Used to indicate whether the address of the call instruction
+/// or the address after the call instruction is listed in the stackmap. For
+/// most runtimes, PostCall safepoints are appropriate.
+///
+enum PointKind {
+ PreCall, ///< Instr is a call instruction.
+ PostCall ///< Instr is the return address of a call.
+};
+
+} // end namespace GC
+
+/// 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.
+
+ unsigned NeededSafePoints = 0; ///< Bitmask of required safe points.
+ bool CustomReadBarriers = false; ///< Default is to insert loads.
+ bool CustomWriteBarriers = false; ///< Default is to insert stores.
+ bool CustomRoots = false; ///< Default is to pass through to backend.
+ bool InitRoots= true; ///< If set, roots are nulled during lowering.
+ 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; }
+
+ /// By default, write barriers are replaced with simple store
+ /// instructions. If true, you must provide a custom pass to lower
+ /// calls to @llvm.gcwrite.
+ bool customWriteBarrier() const { return CustomWriteBarriers; }
+
+ /// By default, read barriers are replaced with simple load
+ /// instructions. If true, you must provide a custom pass to lower
+ /// calls to @llvm.gcread.
+ bool customReadBarrier() const { return CustomReadBarriers; }
+
+ /// 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 of any kind are required. By default, none are
+ /// recorded.
+ bool needsSafePoints() const { return NeededSafePoints != 0; }
+
+ /// True if the given kind of safe point is required. By default, none are
+ /// recorded.
+ bool needsSafePoint(GC::PointKind Kind) const {
+ return (NeededSafePoints & 1 << Kind) != 0;
+ }
+
+ /// By default, roots are left for the code generator so it can generate a
+ /// stack map. If true, you must provide a custom pass to lower
+ /// calls to @llvm.gcroot.
+ bool customRoots() const { return CustomRoots; }
+
+ /// If set, gcroot intrinsics should initialize their allocas to null
+ /// before the first use. This is necessary for most GCs and is enabled by
+ /// default.
+ bool initializeRoots() const { return InitRoots; }
+
+ /// 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