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