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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.
// When requested, the GCStrategy will be populated with data about each
// function which uses it. 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.
#include "llvm/CodeGen/GCMetadata.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/Support/Registry.h"
#include <string>
namespace llvm {
class GCStrategy;
/// The GC strategy registry uses all the defaults from Registry.
typedef Registry<GCStrategy> GCRegistry;
/// GCStrategy describes a garbage collector algorithm's code generation
/// requirements, and provides overridable hooks for those needs which cannot
/// be abstractly described.
class GCStrategy {
typedef std::vector<std::unique_ptr<GCFunctionInfo>> list_type;
typedef list_type::iterator iterator;
friend class GCModuleInfo;
const Module *M;
std::string Name;
list_type Functions;
unsigned NeededSafePoints; ///< Bitmask of required safe points.
bool CustomReadBarriers; ///< Default is to insert loads.
bool CustomWriteBarriers; ///< Default is to insert stores.
bool CustomRoots; ///< Default is to pass through to backend.
bool CustomSafePoints; ///< Default is to use NeededSafePoints
///< to find safe points.
bool InitRoots; ///< If set, roots are nulled during lowering.
bool UsesMetadata; ///< If set, backend must emit metadata tables.
virtual ~GCStrategy() {}
/// getName - The name of the GC strategy, for debugging.
const std::string &getName() const { return Name; }
/// getModule - The module within which the GC strategy is operating.
const Module &getModule() const { return *M; }
/// needsSafePoitns - True if safe points of any kind are required. By
// default, none are recorded.
bool needsSafePoints() const {
return CustomSafePoints || NeededSafePoints != 0;
/// needsSafePoint(Kind) - 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;
/// customWriteBarrier - By default, write barriers are replaced with simple
/// store instructions. If true, then
/// performCustomLowering must instead lower them.
bool customWriteBarrier() const { return CustomWriteBarriers; }
/// customReadBarrier - By default, read barriers are replaced with simple
/// load instructions. If true, then
/// performCustomLowering must instead lower them.
bool customReadBarrier() const { return CustomReadBarriers; }
/// customRoots - By default, roots are left for the code generator so it
/// can generate a stack map. If true, then
// performCustomLowering must delete them.
bool customRoots() const { return CustomRoots; }
/// customSafePoints - By default, the GC analysis will find safe
/// points according to NeededSafePoints. If true,
/// then findCustomSafePoints must create them.
bool customSafePoints() const { return CustomSafePoints; }
/// initializeRoots - 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; }
/// usesMetadata - If set, appropriate metadata tables must be emitted by
/// the back-end (assembler, JIT, or otherwise).
bool usesMetadata() const { return UsesMetadata; }
/// begin/end - Iterators for function metadata.
iterator begin() { return Functions.begin(); }
iterator end() { return Functions.end(); }
/// insertFunctionMetadata - Creates metadata for a function.
GCFunctionInfo *insertFunctionInfo(const Function &F);
/// initializeCustomLowering/performCustomLowering - If any of the actions
/// are set to custom, performCustomLowering must be overriden to transform
/// the corresponding actions to LLVM IR. initializeCustomLowering is
/// optional to override. These are the only GCStrategy methods through
/// which the LLVM IR can be modified.
virtual bool initializeCustomLowering(Module &F);
virtual bool performCustomLowering(Function &F);
virtual bool findCustomSafePoints(GCFunctionInfo& FI, MachineFunction& MF);