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20e9049509
Reland https://github.com/llvm/llvm-project/pull/83237 --- (Original comments) Currently all the specializations of a template (including instantiation, specialization and partial specializations) will be loaded at once if we want to instantiate another instance for the template, or find instantiation for the template, or just want to complete the redecl chain. This means basically we need to load every specializations for the template once the template declaration got loaded. This is bad since when we load a specialization, we need to load all of its template arguments. Then we have to deserialize a lot of unnecessary declarations. For example, ``` // M.cppm export module M; export template <class T> class A {}; export class ShouldNotBeLoaded {}; export class Temp { A<ShouldNotBeLoaded> AS; }; // use.cpp import M; A<int> a; ``` We have a specialization ` A<ShouldNotBeLoaded>` in `M.cppm` and we instantiate the template `A` in `use.cpp`. Then we will deserialize `ShouldNotBeLoaded` surprisingly when compiling `use.cpp`. And this patch tries to avoid that. Given that the templates are heavily used in C++, this is a pain point for the performance. This patch adds MultiOnDiskHashTable for specializations in the ASTReader. Then we will only deserialize the specializations with the same template arguments. We made that by using ODRHash for the template arguments as the key of the hash table. To review this patch, I think `ASTReaderDecl::AddLazySpecializations` may be a good entry point.
110 lines
3.9 KiB
C++
110 lines
3.9 KiB
C++
//===- ASTCommon.h - Common stuff for ASTReader/ASTWriter -*- 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 common functions that both ASTReader and ASTWriter use.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_CLANG_LIB_SERIALIZATION_ASTCOMMON_H
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#define LLVM_CLANG_LIB_SERIALIZATION_ASTCOMMON_H
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#include "clang/AST/ASTContext.h"
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#include "clang/AST/DeclFriend.h"
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#include "clang/Basic/LLVM.h"
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#include "clang/Serialization/ASTBitCodes.h"
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namespace clang {
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namespace serialization {
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enum DeclUpdateKind {
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UPD_CXX_ADDED_IMPLICIT_MEMBER,
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UPD_CXX_ADDED_ANONYMOUS_NAMESPACE,
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UPD_CXX_ADDED_FUNCTION_DEFINITION,
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UPD_CXX_ADDED_VAR_DEFINITION,
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UPD_CXX_POINT_OF_INSTANTIATION,
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UPD_CXX_INSTANTIATED_CLASS_DEFINITION,
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UPD_CXX_INSTANTIATED_DEFAULT_ARGUMENT,
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UPD_CXX_INSTANTIATED_DEFAULT_MEMBER_INITIALIZER,
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UPD_CXX_RESOLVED_DTOR_DELETE,
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UPD_CXX_RESOLVED_EXCEPTION_SPEC,
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UPD_CXX_DEDUCED_RETURN_TYPE,
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UPD_DECL_MARKED_USED,
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UPD_MANGLING_NUMBER,
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UPD_STATIC_LOCAL_NUMBER,
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UPD_DECL_MARKED_OPENMP_THREADPRIVATE,
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UPD_DECL_MARKED_OPENMP_ALLOCATE,
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UPD_DECL_MARKED_OPENMP_DECLARETARGET,
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UPD_DECL_EXPORTED,
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UPD_ADDED_ATTR_TO_RECORD
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};
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TypeIdx TypeIdxFromBuiltin(const BuiltinType *BT);
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unsigned ComputeHash(Selector Sel);
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/// Retrieve the "definitive" declaration that provides all of the
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/// visible entries for the given declaration context, if there is one.
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///
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/// The "definitive" declaration is the only place where we need to look to
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/// find information about the declarations within the given declaration
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/// context. For example, C++ and Objective-C classes, C structs/unions, and
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/// Objective-C protocols, categories, and extensions are all defined in a
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/// single place in the source code, so they have definitive declarations
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/// associated with them. C++ namespaces, on the other hand, can have
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/// multiple definitions.
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const DeclContext *getDefinitiveDeclContext(const DeclContext *DC);
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/// Determine whether the given declaration kind is redeclarable.
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bool isRedeclarableDeclKind(unsigned Kind);
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/// Determine whether the given declaration needs an anonymous
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/// declaration number.
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bool needsAnonymousDeclarationNumber(const NamedDecl *D);
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/// Visit each declaration within \c DC that needs an anonymous
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/// declaration number and call \p Visit with the declaration and its number.
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template<typename Fn> void numberAnonymousDeclsWithin(const DeclContext *DC,
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Fn Visit) {
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unsigned Index = 0;
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for (Decl *LexicalD : DC->decls()) {
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// For a friend decl, we care about the declaration within it, if any.
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if (auto *FD = dyn_cast<FriendDecl>(LexicalD))
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LexicalD = FD->getFriendDecl();
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auto *ND = dyn_cast_or_null<NamedDecl>(LexicalD);
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if (!ND || !needsAnonymousDeclarationNumber(ND))
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continue;
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Visit(ND, Index++);
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}
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}
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/// Determine whether the given declaration will be included in the per-module
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/// initializer if it needs to be eagerly handed to the AST consumer. If so, we
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/// should not hand it to the consumer when deserializing it, nor include it in
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/// the list of eagerly deserialized declarations.
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inline bool isPartOfPerModuleInitializer(const Decl *D) {
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if (isa<ImportDecl>(D))
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return true;
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// Template instantiations are notionally in an "instantiation unit" rather
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// than in any particular translation unit, so they need not be part of any
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// particular (sub)module's per-module initializer.
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if (auto *VD = dyn_cast<VarDecl>(D))
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return !isTemplateInstantiation(VD->getTemplateSpecializationKind());
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return false;
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}
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void updateModuleTimestamp(StringRef ModuleFilename);
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} // namespace serialization
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} // namespace clang
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#endif
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