1//===- Memory.h -------------------------------------------------*- 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 defines arena allocators.
10//
11// Almost all large objects, such as files, sections or symbols, are
12// used for the entire lifetime of the linker once they are created.
13// This usage characteristic makes arena allocator an attractive choice
14// where the entire linker is one arena. With an arena, newly created
15// objects belong to the arena and freed all at once when everything is done.
16// Arena allocators are efficient and easy to understand.
17// Most objects are allocated using the arena allocators defined by this file.
18//
19//===----------------------------------------------------------------------===//
20
21#ifndef LLD_COMMON_MEMORY_H
22#define LLD_COMMON_MEMORY_H
23
24#include "llvm/Support/Allocator.h"
25
26namespace lld {
27// A base class only used by the CommonLinkerContext to keep track of the
28// SpecificAlloc<> instances.
29struct SpecificAllocBase {
30 virtual ~SpecificAllocBase() = default;
31 static SpecificAllocBase *getOrCreate(void *tag, size_t size, size_t align,
32 SpecificAllocBase *(&creator)(void *));
33};
34
35// An arena of specific types T, created on-demand.
36template <class T> struct SpecificAlloc : public SpecificAllocBase {
37 static SpecificAllocBase *create(void *storage) {
38 return new (storage) SpecificAlloc<T>();
39 }
40 llvm::SpecificBumpPtrAllocator<T> alloc;
41 static int tag;
42};
43
44// The address of this static member is only used as a key in
45// CommonLinkerContext::instances. Its value does not matter.
46template <class T> int SpecificAlloc<T>::tag = 0;
47
48// Creates the arena on-demand on the first call; or returns it, if it was
49// already created.
50template <typename T>
51inline llvm::SpecificBumpPtrAllocator<T> &getSpecificAllocSingleton() {
52 SpecificAllocBase *instance = SpecificAllocBase::getOrCreate(
53 tag: &SpecificAlloc<T>::tag, size: sizeof(SpecificAlloc<T>),
54 align: alignof(SpecificAlloc<T>), creator&: SpecificAlloc<T>::create);
55 return ((SpecificAlloc<T> *)instance)->alloc;
56}
57
58// Creates new instances of T off a (almost) contiguous arena/object pool. The
59// instances are destroyed whenever lldMain() goes out of scope.
60template <typename T, typename... U> T *make(U &&... args) {
61 return new (getSpecificAllocSingleton<T>().Allocate())
62 T(std::forward<U>(args)...);
63}
64
65template <typename T>
66inline llvm::SpecificBumpPtrAllocator<T> &
67getSpecificAllocSingletonThreadLocal() {
68 thread_local SpecificAlloc<T> instance;
69 return instance.alloc;
70}
71
72// Create a new instance of T off a thread-local SpecificAlloc, used by code
73// like parallel input section initialization. The use cases assume that the
74// return value outlives the containing parallelForEach (if exists), which is
75// currently guaranteed: when parallelForEach returns, the threads allocating
76// the TLS are not destroyed.
77//
78// Note: Some ports (e.g. ELF) have lots of global states which are currently
79// infeasible to remove, and context() just adds overhead with no benefit. The
80// allocation performance is of higher importance, so we simply use thread_local
81// allocators instead of doing context indirection and pthread_getspecific.
82template <typename T, typename... U> T *makeThreadLocal(U &&...args) {
83 return new (getSpecificAllocSingletonThreadLocal<T>().Allocate())
84 T(std::forward<U>(args)...);
85}
86
87template <typename T> T *makeThreadLocalN(size_t n) {
88 return new (getSpecificAllocSingletonThreadLocal<T>().Allocate(n)) T[n];
89}
90
91} // namespace lld
92
93#endif
94

source code of lld/include/lld/Common/Memory.h