1//===- GCMetadata.h - Garbage collector metadata ----------------*- C++ -*-===//
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 declares the GCFunctionInfo and GCModuleInfo classes, which are
10// used as a communication channel from the target code generator to the target
11// garbage collectors. This interface allows code generators and garbage
12// collectors to be developed independently.
13//
14// The GCFunctionInfo class logs the data necessary to build a type accurate
15// stack map. The code generator outputs:
16//
17//   - Safe points as specified by the GCStrategy's NeededSafePoints.
18//   - Stack offsets for GC roots, as specified by calls to llvm.gcroot
19//
20// As a refinement, liveness analysis calculates the set of live roots at each
21// safe point. Liveness analysis is not presently performed by the code
22// generator, so all roots are assumed live.
23//
24// GCModuleInfo simply collects GCFunctionInfo instances for each Function as
25// they are compiled. This accretion is necessary for collectors which must emit
26// a stack map for the compilation unit as a whole. Therefore, GCFunctionInfo
27// outlives the MachineFunction from which it is derived and must not refer to
28// any code generator data structures.
29//
30//===----------------------------------------------------------------------===//
31
32#ifndef LLVM_CODEGEN_GCMETADATA_H
33#define LLVM_CODEGEN_GCMETADATA_H
34
35#include "llvm/ADT/DenseMap.h"
36#include "llvm/ADT/SmallVector.h"
37#include "llvm/ADT/StringMap.h"
38#include "llvm/ADT/StringRef.h"
39#include "llvm/CodeGen/GCStrategy.h"
40#include "llvm/IR/DebugLoc.h"
41#include "llvm/Pass.h"
42#include <algorithm>
43#include <cstddef>
44#include <cstdint>
45#include <memory>
46#include <vector>
47
48namespace llvm {
49
50class Constant;
51class Function;
52class MCSymbol;
53
54/// GCPoint - Metadata for a collector-safe point in machine code.
55///
56struct GCPoint {
57  MCSymbol *Label;    ///< A label.
58  DebugLoc Loc;
59
60  GCPoint(MCSymbol *L, DebugLoc DL)
61      : Label(L), Loc(std::move(DL)) {}
62};
63
64/// GCRoot - Metadata for a pointer to an object managed by the garbage
65/// collector.
66struct GCRoot {
67  int Num;                  ///< Usually a frame index.
68  int StackOffset = -1;     ///< Offset from the stack pointer.
69  const Constant *Metadata; ///< Metadata straight from the call
70                            ///< to llvm.gcroot.
71
72  GCRoot(int N, const Constant *MD) : Num(N), Metadata(MD) {}
73};
74
75/// Garbage collection metadata for a single function.  Currently, this
76/// information only applies to GCStrategies which use GCRoot.
77class GCFunctionInfo {
78public:
79  using iterator = std::vector<GCPoint>::iterator;
80  using roots_iterator = std::vector<GCRoot>::iterator;
81  using live_iterator = std::vector<GCRoot>::const_iterator;
82
83private:
84  const Function &F;
85  GCStrategy &S;
86  uint64_t FrameSize;
87  std::vector<GCRoot> Roots;
88  std::vector<GCPoint> SafePoints;
89
90  // FIXME: Liveness. A 2D BitVector, perhaps?
91  //
92  //   BitVector Liveness;
93  //
94  //   bool islive(int point, int root) =
95  //     Liveness[point * SafePoints.size() + root]
96  //
97  // The bit vector is the more compact representation where >3.2% of roots
98  // are live per safe point (1.5% on 64-bit hosts).
99
100public:
101  GCFunctionInfo(const Function &F, GCStrategy &S);
102  ~GCFunctionInfo();
103
104  /// getFunction - Return the function to which this metadata applies.
105  const Function &getFunction() const { return F; }
106
107  /// getStrategy - Return the GC strategy for the function.
108  GCStrategy &getStrategy() { return S; }
109
110  /// addStackRoot - Registers a root that lives on the stack. Num is the
111  ///                stack object ID for the alloca (if the code generator is
112  //                 using  MachineFrameInfo).
113  void addStackRoot(int Num, const Constant *Metadata) {
114    Roots.push_back(GCRoot(Num, Metadata));
115  }
116
117  /// removeStackRoot - Removes a root.
118  roots_iterator removeStackRoot(roots_iterator position) {
119    return Roots.erase(position);
120  }
121
122  /// addSafePoint - Notes the existence of a safe point. Num is the ID of the
123  /// label just prior to the safe point (if the code generator is using
124  /// MachineModuleInfo).
125  void addSafePoint(MCSymbol *Label, const DebugLoc &DL) {
126    SafePoints.emplace_back(Label, DL);
127  }
128
129  /// getFrameSize/setFrameSize - Records the function's frame size.
130  uint64_t getFrameSize() const { return FrameSize; }
131  void setFrameSize(uint64_t S) { FrameSize = S; }
132
133  /// begin/end - Iterators for safe points.
134  iterator begin() { return SafePoints.begin(); }
135  iterator end() { return SafePoints.end(); }
136  size_t size() const { return SafePoints.size(); }
137
138  /// roots_begin/roots_end - Iterators for all roots in the function.
139  roots_iterator roots_begin() { return Roots.begin(); }
140  roots_iterator roots_end() { return Roots.end(); }
141  size_t roots_size() const { return Roots.size(); }
142
143  /// live_begin/live_end - Iterators for live roots at a given safe point.
144  live_iterator live_begin(const iterator &p) { return roots_begin(); }
145  live_iterator live_end(const iterator &p) { return roots_end(); }
146  size_t live_size(const iterator &p) const { return roots_size(); }
147};
148
149/// An analysis pass which caches information about the entire Module.
150/// Records both the function level information used by GCRoots and a
151/// cache of the 'active' gc strategy objects for the current Module.
152class GCModuleInfo : public ImmutablePass {
153  /// An owning list of all GCStrategies which have been created
154  SmallVector<std::unique_ptr<GCStrategy>, 1> GCStrategyList;
155  /// A helper map to speedup lookups into the above list
156  StringMap<GCStrategy*> GCStrategyMap;
157
158public:
159  /// Lookup the GCStrategy object associated with the given gc name.
160  /// Objects are owned internally; No caller should attempt to delete the
161  /// returned objects.
162  GCStrategy *getGCStrategy(const StringRef Name);
163
164  /// List of per function info objects.  In theory, Each of these
165  /// may be associated with a different GC.
166  using FuncInfoVec = std::vector<std::unique_ptr<GCFunctionInfo>>;
167
168  FuncInfoVec::iterator funcinfo_begin() { return Functions.begin(); }
169  FuncInfoVec::iterator funcinfo_end() { return Functions.end(); }
170
171private:
172  /// Owning list of all GCFunctionInfos associated with this Module
173  FuncInfoVec Functions;
174
175  /// Non-owning map to bypass linear search when finding the GCFunctionInfo
176  /// associated with a particular Function.
177  using finfo_map_type = DenseMap<const Function *, GCFunctionInfo *>;
178  finfo_map_type FInfoMap;
179
180public:
181  using iterator = SmallVector<std::unique_ptr<GCStrategy>, 1>::const_iterator;
182
183  static char ID;
184
185  GCModuleInfo();
186
187  /// clear - Resets the pass. Any pass, which uses GCModuleInfo, should
188  /// call it in doFinalization().
189  ///
190  void clear();
191
192  /// begin/end - Iterators for used strategies.
193  ///
194  iterator begin() const { return GCStrategyList.begin(); }
195  iterator end() const { return GCStrategyList.end(); }
196
197  /// get - Look up function metadata.  This is currently assumed
198  /// have the side effect of initializing the associated GCStrategy.  That
199  /// will soon change.
200  GCFunctionInfo &getFunctionInfo(const Function &F);
201};
202
203} // end namespace llvm
204
205#endif // LLVM_CODEGEN_GCMETADATA_H
206