94 lines
3.7 KiB
C++
94 lines
3.7 KiB
C++
//===- Memory.h -------------------------------------------------*- C++ -*-===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This file defines arena allocators.
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//
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// Almost all large objects, such as files, sections or symbols, are
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// used for the entire lifetime of the linker once they are created.
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// This usage characteristic makes arena allocator an attractive choice
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// where the entire linker is one arena. With an arena, newly created
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// objects belong to the arena and freed all at once when everything is done.
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// Arena allocators are efficient and easy to understand.
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// Most objects are allocated using the arena allocators defined by this file.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLD_COMMON_MEMORY_H
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#define LLD_COMMON_MEMORY_H
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#include "llvm/Support/Allocator.h"
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namespace lld {
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// A base class only used by the CommonLinkerContext to keep track of the
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// SpecificAlloc<> instances.
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struct SpecificAllocBase {
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virtual ~SpecificAllocBase() = default;
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static SpecificAllocBase *getOrCreate(void *tag, size_t size, size_t align,
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SpecificAllocBase *(&creator)(void *));
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};
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// An arena of specific types T, created on-demand.
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template <class T> struct SpecificAlloc : public SpecificAllocBase {
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static SpecificAllocBase *create(void *storage) {
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return new (storage) SpecificAlloc<T>();
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}
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llvm::SpecificBumpPtrAllocator<T> alloc;
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static int tag;
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};
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// The address of this static member is only used as a key in
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// CommonLinkerContext::instances. Its value does not matter.
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template <class T> int SpecificAlloc<T>::tag = 0;
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// Creates the arena on-demand on the first call; or returns it, if it was
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// already created.
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template <typename T>
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inline llvm::SpecificBumpPtrAllocator<T> &getSpecificAllocSingleton() {
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SpecificAllocBase *instance = SpecificAllocBase::getOrCreate(
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&SpecificAlloc<T>::tag, sizeof(SpecificAlloc<T>),
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alignof(SpecificAlloc<T>), SpecificAlloc<T>::create);
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return ((SpecificAlloc<T> *)instance)->alloc;
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}
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// Creates new instances of T off a (almost) contiguous arena/object pool. The
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// instances are destroyed whenever lldMain() goes out of scope.
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template <typename T, typename... U> T *make(U &&... args) {
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return new (getSpecificAllocSingleton<T>().Allocate())
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T(std::forward<U>(args)...);
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}
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template <typename T>
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inline llvm::SpecificBumpPtrAllocator<T> &
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getSpecificAllocSingletonThreadLocal() {
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thread_local SpecificAlloc<T> instance;
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return instance.alloc;
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}
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// Create a new instance of T off a thread-local SpecificAlloc, used by code
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// like parallel input section initialization. The use cases assume that the
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// return value outlives the containing parallelForEach (if exists), which is
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// currently guaranteed: when parallelForEach returns, the threads allocating
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// the TLS are not destroyed.
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//
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// Note: Some ports (e.g. ELF) have lots of global states which are currently
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// infeasible to remove, and context() just adds overhead with no benefit. The
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// allocation performance is of higher importance, so we simply use thread_local
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// allocators instead of doing context indirection and pthread_getspecific.
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template <typename T, typename... U> T *makeThreadLocal(U &&...args) {
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return new (getSpecificAllocSingletonThreadLocal<T>().Allocate())
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T(std::forward<U>(args)...);
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}
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template <typename T> T *makeThreadLocalN(size_t n) {
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return new (getSpecificAllocSingletonThreadLocal<T>().Allocate(n)) T[n];
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}
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} // namespace lld
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#endif
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