[clangd] Get rid of AST matchers in SymbolCollector. NFC

[ioeric]

Summary

The AST matcher pops up in performance profile. Although not the most expensive thing we could optimize, this still brings indexAST latency from ~5.3s to ~4.4s for a large TU with big preamble.

[kadircet]

LGTM

[malaperle]

why?

[ioeric]

In D52089#1235777, @malaperle wrote:

why?

I wanted to get some numbers and update the patch summary, but somehow forgot. Sorry about that and thanks for asking!

The AST matcher pops up in performance profile. Although not the most expensive thing we could optimize, this still brings indexAST latency from ~5.3s to ~4.4s for a large TU with big preamble.

[malaperle]

In D52089#1235851, @ioeric wrote:

In D52089#1235777, @malaperle wrote:

why?

I wanted to get some numbers and update the patch summary, but somehow forgot. Sorry about that and thanks for asking!

The AST matcher pops up in performance profile. Although not the most expensive thing we could optimize, this still brings indexAST latency from ~5.3s to ~4.4s for a large TU with big preamble.

Thanks! That's what I was looking for :) Sounds good to me.

clangd/index/SymbolCollector.cpp

 #include "SymbolCollector.h"
 #include "AST.h"
 #include "CanonicalIncludes.h"
 #include "CodeComplete.h"
 #include "CodeCompletionStrings.h"
 #include "Logger.h"
 #include "SourceCode.h"
 #include "URI.h"
+#include "clang/AST/Decl.h"
+#include "clang/AST/DeclBase.h"
 #include "clang/AST/DeclCXX.h"
 #include "clang/AST/DeclTemplate.h"
 #include "clang/ASTMatchers/ASTMatchFinder.h"
 #include "clang/Basic/SourceManager.h"
+#include "clang/Basic/Specifiers.h"
 #include "clang/Index/IndexSymbol.h"
 #include "clang/Index/USRGeneration.h"
+#include "llvm/Support/Casting.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/Path.h"
 
 namespace clang {
 namespace clangd {
 
 namespace {
return (Roles & static_cast<unsigned>(index::SymbolRole::Definition)) &&
          llvm::isa<TagDecl>(&ND) &&
          match(decl(isExpansionInMainFile()), ND, ND.getASTContext()).empty();
 }
 
 RefKind toRefKind(index::SymbolRoleSet Roles) {
   return static_cast<RefKind>(static_cast<unsigned>(RefKind::All) & Roles);
 }
 
+template <class T> bool explicitTemplateSpecialization(const NamedDecl &ND) {
+  if (const auto *TD = llvm::dyn_cast<T>(&ND))
+    if (TD->getTemplateSpecializationKind() == TSK_ExplicitSpecialization)
+      return true;
+  return false;
+}
+
 } // namespace
 
 SymbolCollector::SymbolCollector(Options Opts) : Opts(std::move(Opts)) {}
 
 void SymbolCollector::initialize(ASTContext &Ctx) {
   ASTCtx = &Ctx;
   CompletionAllocator = std::make_shared<GlobalCodeCompletionAllocator>();
   CompletionTUInfo =
bool SymbolCollector::shouldCollectSymbol(const NamedDecl &ND,
   // violations.
   if (ND.isInAnonymousNamespace())
     return false;
 
   // We want most things but not "local" symbols such as symbols inside
   // FunctionDecl, BlockDecl, ObjCMethodDecl and OMPDeclareReductionDecl.
   // FIXME: Need a matcher for ExportDecl in order to include symbols declared
   // within an export.
-  auto InNonLocalContext = hasDeclContext(anyOf(
-      translationUnitDecl(), namespaceDecl(), linkageSpecDecl(), recordDecl(),
-      enumDecl(), objcProtocolDecl(), objcInterfaceDecl(), objcCategoryDecl(),
-      objcCategoryImplDecl(), objcImplementationDecl()));
-  // Don't index template specializations and expansions in main files.
-  auto IsSpecialization =
-      anyOf(functionDecl(isExplicitTemplateSpecialization()),
-            cxxRecordDecl(isExplicitTemplateSpecialization()),
-            varDecl(isExplicitTemplateSpecialization()));
-  if (match(decl(allOf(unless(isExpansionInMainFile()), InNonLocalContext,
-                       unless(IsSpecialization))),
-            ND, ASTCtx)
-          .empty())
+  const auto *DeclCtx = ND.getDeclContext();
+  switch (DeclCtx->getDeclKind()) {
+  case Decl::TranslationUnit:
+  case Decl::Namespace:
+  case Decl::LinkageSpec:
+  case Decl::Enum:
+  case Decl::ObjCProtocol:
+  case Decl::ObjCInterface:
+  case Decl::ObjCCategory:
+  case Decl::ObjCCategoryImpl:
+  case Decl::ObjCImplementation:
+    break;
+  default:
+    // Record has a few derivations (e.g. CXXRecord, Class specialization), it's
+    // easier to cast.
+    if (!llvm::isa<RecordDecl>(DeclCtx))
+      return false;
+  }
+  if (explicitTemplateSpecialization<FunctionDecl>(ND) ||
+      explicitTemplateSpecialization<CXXRecordDecl>(ND) ||
+      explicitTemplateSpecialization<VarDecl>(ND))
     return false;
 
+  const auto &SM = ASTCtx.getSourceManager();
+  // Skip decls in the main file.
+  if (SM.isInMainFile(SM.getExpansionLoc(ND.getBeginLoc())))
+    return false;
   // Avoid indexing internal symbols in protobuf generated headers.
   if (isPrivateProtoDecl(ND))
     return false;
   return true;
 }
 
 // Always return true to continue indexing.
 bool SymbolCollector::handleDeclOccurence(