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//===- GCMetadata.h - Garbage collector metadata ----------------*- C++ -*-===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// This file declares the GCFunctionInfo and GCModuleInfo classes, which are
// used as a communication channel from the target code generator to the target
// garbage collectors. This interface allows code generators and garbage
// collectors to be developed independently.
// The GCFunctionInfo class logs the data necessary to build a type accurate
// stack map. The code generator outputs:
// - Safe points as specified by the GCStrategy's NeededSafePoints.
// - Stack offsets for GC roots, as specified by calls to llvm.gcroot
// As a refinement, liveness analysis calculates the set of live roots at each
// safe point. Liveness analysis is not presently performed by the code
// generator, so all roots are assumed live.
// GCModuleInfo simply collects GCFunctionInfo instances for each Function as
// they are compiled. This accretion is necessary for collectors which must emit
// a stack map for the compilation unit as a whole. Therefore, GCFunctionInfo
// outlives the MachineFunction from which it is derived and must not refer to
// any code generator data structures.
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/CodeGen/GCStrategy.h"
#include "llvm/IR/DebugLoc.h"
#include "llvm/Pass.h"
#include <algorithm>
#include <cstddef>
#include <cstdint>
#include <memory>
#include <vector>
namespace llvm {
class Constant;
class Function;
class MCSymbol;
/// GCPoint - Metadata for a collector-safe point in machine code.
struct GCPoint {
MCSymbol *Label; ///< A label.
DebugLoc Loc;
GCPoint(MCSymbol *L, DebugLoc DL)
: Label(L), Loc(std::move(DL)) {}
/// GCRoot - Metadata for a pointer to an object managed by the garbage
/// collector.
struct GCRoot {
int Num; ///< Usually a frame index.
int StackOffset = -1; ///< Offset from the stack pointer.
const Constant *Metadata; ///< Metadata straight from the call
///< to llvm.gcroot.
GCRoot(int N, const Constant *MD) : Num(N), Metadata(MD) {}
/// Garbage collection metadata for a single function. Currently, this
/// information only applies to GCStrategies which use GCRoot.
class GCFunctionInfo {
using iterator = std::vector<GCPoint>::iterator;
using roots_iterator = std::vector<GCRoot>::iterator;
using live_iterator = std::vector<GCRoot>::const_iterator;
const Function &F;
GCStrategy &S;
uint64_t FrameSize;
std::vector<GCRoot> Roots;
std::vector<GCPoint> SafePoints;
// FIXME: Liveness. A 2D BitVector, perhaps?
// BitVector Liveness;
// bool islive(int point, int root) =
// Liveness[point * SafePoints.size() + root]
// The bit vector is the more compact representation where >3.2% of roots
// are live per safe point (1.5% on 64-bit hosts).
GCFunctionInfo(const Function &F, GCStrategy &S);
/// getFunction - Return the function to which this metadata applies.
const Function &getFunction() const { return F; }
/// getStrategy - Return the GC strategy for the function.
GCStrategy &getStrategy() { return S; }
/// addStackRoot - Registers a root that lives on the stack. Num is the
/// stack object ID for the alloca (if the code generator is
// using MachineFrameInfo).
void addStackRoot(int Num, const Constant *Metadata) {
Roots.push_back(GCRoot(Num, Metadata));
/// removeStackRoot - Removes a root.
roots_iterator removeStackRoot(roots_iterator position) {
return Roots.erase(position);
/// addSafePoint - Notes the existence of a safe point. Num is the ID of the
/// label just prior to the safe point (if the code generator is using
/// MachineModuleInfo).
void addSafePoint(MCSymbol *Label, const DebugLoc &DL) {
SafePoints.emplace_back(Label, DL);
/// getFrameSize/setFrameSize - Records the function's frame size.
uint64_t getFrameSize() const { return FrameSize; }
void setFrameSize(uint64_t S) { FrameSize = S; }
/// begin/end - Iterators for safe points.
iterator begin() { return SafePoints.begin(); }
iterator end() { return SafePoints.end(); }
size_t size() const { return SafePoints.size(); }
/// roots_begin/roots_end - Iterators for all roots in the function.
roots_iterator roots_begin() { return Roots.begin(); }
roots_iterator roots_end() { return Roots.end(); }
size_t roots_size() const { return Roots.size(); }
/// live_begin/live_end - Iterators for live roots at a given safe point.
live_iterator live_begin(const iterator &p) { return roots_begin(); }
live_iterator live_end(const iterator &p) { return roots_end(); }
size_t live_size(const iterator &p) const { return roots_size(); }
/// An analysis pass which caches information about the entire Module.
/// Records both the function level information used by GCRoots and a
/// cache of the 'active' gc strategy objects for the current Module.
class GCModuleInfo : public ImmutablePass {
/// An owning list of all GCStrategies which have been created
SmallVector<std::unique_ptr<GCStrategy>, 1> GCStrategyList;
/// A helper map to speedup lookups into the above list
StringMap<GCStrategy*> GCStrategyMap;
/// Lookup the GCStrategy object associated with the given gc name.
/// Objects are owned internally; No caller should attempt to delete the
/// returned objects.
GCStrategy *getGCStrategy(const StringRef Name);
/// List of per function info objects. In theory, Each of these
/// may be associated with a different GC.
using FuncInfoVec = std::vector<std::unique_ptr<GCFunctionInfo>>;
FuncInfoVec::iterator funcinfo_begin() { return Functions.begin(); }
FuncInfoVec::iterator funcinfo_end() { return Functions.end(); }
/// Owning list of all GCFunctionInfos associated with this Module
FuncInfoVec Functions;
/// Non-owning map to bypass linear search when finding the GCFunctionInfo
/// associated with a particular Function.
using finfo_map_type = DenseMap<const Function *, GCFunctionInfo *>;
finfo_map_type FInfoMap;
using iterator = SmallVector<std::unique_ptr<GCStrategy>, 1>::const_iterator;
static char ID;
/// clear - Resets the pass. Any pass, which uses GCModuleInfo, should
/// call it in doFinalization().
void clear();
/// begin/end - Iterators for used strategies.
iterator begin() const { return GCStrategyList.begin(); }
iterator end() const { return GCStrategyList.end(); }
/// get - Look up function metadata. This is currently assumed
/// have the side effect of initializing the associated GCStrategy. That
/// will soon change.
GCFunctionInfo &getFunctionInfo(const Function &F);
} // end namespace llvm