From 4b43489e894f9667c319d0dceee5969dc5ac2f02 Mon Sep 17 00:00:00 2001
From: Richard Smith <richard-llvm@metafoo.co.uk>
Date: Fri, 6 May 2016 23:14:07 +0000
Subject: [PATCH] [modules] Attempt to improve performance for declaration
 merging without a Sema object in C. Rather than using the DeclContext (which
 is very slow because it triggers us to build a lookup table for the
 DeclContext), use a separate map from identifiers to decls for this case,
 containing only the ones we've actually deserialized. For convenience, this
 map is implemented as an IdentifierResolver.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@268817 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/clang/Serialization/ASTReader.h | 11 +++++++++++
 lib/Serialization/ASTReader.cpp         |  5 +++++
 lib/Serialization/ASTReaderDecl.cpp     |  9 ++++-----
 3 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/include/clang/Serialization/ASTReader.h b/include/clang/Serialization/ASTReader.h
index 6e1cb0a916..1b40494fd4 100644
--- a/include/clang/Serialization/ASTReader.h
+++ b/include/clang/Serialization/ASTReader.h
@@ -27,6 +27,7 @@
 #include "clang/Lex/HeaderSearch.h"
 #include "clang/Lex/PreprocessingRecord.h"
 #include "clang/Sema/ExternalSemaSource.h"
+#include "clang/Sema/IdentifierResolver.h"
 #include "clang/Serialization/ASTBitCodes.h"
 #include "clang/Serialization/ContinuousRangeMap.h"
 #include "clang/Serialization/Module.h"
@@ -390,6 +391,11 @@ private:
   /// \brief The module manager which manages modules and their dependencies
   ModuleManager ModuleMgr;
 
+  /// \brief A dummy identifier resolver used to merge TU-scope declarations in
+  /// C, for the cases where we don't have a Sema object to provide a real
+  /// identifier resolver.
+  IdentifierResolver DummyIdResolver;
+
   /// A mapping from extension block names to module file extensions.
   llvm::StringMap<IntrusiveRefCntPtr<ModuleFileExtension>> ModuleFileExtensions;
 
@@ -2100,6 +2106,11 @@ public:
   /// imported.
   Sema *getSema() { return SemaObj; }
 
+  /// \brief Get the identifier resolver used for name lookup / updates
+  /// in the translation unit scope. We have one of these even if we don't
+  /// have a Sema object.
+  IdentifierResolver &getIdResolver();
+
   /// \brief Retrieve the identifier table associated with the
   /// preprocessor.
   IdentifierTable &getIdentifierTable();
diff --git a/lib/Serialization/ASTReader.cpp b/lib/Serialization/ASTReader.cpp
index e33cccbd95..5d459ac9fb 100644
--- a/lib/Serialization/ASTReader.cpp
+++ b/lib/Serialization/ASTReader.cpp
@@ -8695,6 +8695,7 @@ ASTReader::ASTReader(
       FileMgr(PP.getFileManager()), PCHContainerRdr(PCHContainerRdr),
       Diags(PP.getDiagnostics()), SemaObj(nullptr), PP(PP), Context(Context),
       Consumer(nullptr), ModuleMgr(PP.getFileManager(), PCHContainerRdr),
+      DummyIdResolver(PP),
       ReadTimer(std::move(ReadTimer)),
       PragmaMSStructState(-1),
       PragmaMSPointersToMembersState(-1),
@@ -8733,3 +8734,7 @@ ASTReader::~ASTReader() {
   if (OwnsDeserializationListener)
     delete DeserializationListener;
 }
+
+IdentifierResolver &ASTReader::getIdResolver() {
+  return SemaObj ? SemaObj->IdResolver : DummyIdResolver;
+}
diff --git a/lib/Serialization/ASTReaderDecl.cpp b/lib/Serialization/ASTReaderDecl.cpp
index a6e993885a..1a013cee21 100644
--- a/lib/Serialization/ASTReaderDecl.cpp
+++ b/lib/Serialization/ASTReaderDecl.cpp
@@ -23,7 +23,6 @@
 #include "clang/AST/DeclVisitor.h"
 #include "clang/AST/Expr.h"
 #include "clang/Sema/IdentifierResolver.h"
-#include "clang/Sema/Sema.h"
 #include "clang/Sema/SemaDiagnostic.h"
 #include "llvm/Support/SaveAndRestore.h"
 
@@ -2814,9 +2813,9 @@ ASTDeclReader::FindExistingResult::~FindExistingResult() {
   if (needsAnonymousDeclarationNumber(New)) {
     setAnonymousDeclForMerging(Reader, New->getLexicalDeclContext(),
                                AnonymousDeclNumber, New);
-  } else if (DC->isTranslationUnit() && Reader.SemaObj &&
+  } else if (DC->isTranslationUnit() &&
              !Reader.getContext().getLangOpts().CPlusPlus) {
-    if (Reader.SemaObj->IdResolver.tryAddTopLevelDecl(New, Name))
+    if (Reader.getIdResolver().tryAddTopLevelDecl(New, Name))
       Reader.PendingFakeLookupResults[Name.getAsIdentifierInfo()]
             .push_back(New);
   } else if (DeclContext *MergeDC = getPrimaryContextForMerging(Reader, DC)) {
@@ -2919,9 +2918,9 @@ ASTDeclReader::FindExistingResult ASTDeclReader::findExisting(NamedDecl *D) {
       if (isSameEntity(Existing, D))
         return FindExistingResult(Reader, D, Existing, AnonymousDeclNumber,
                                   TypedefNameForLinkage);
-  } else if (DC->isTranslationUnit() && Reader.SemaObj &&
+  } else if (DC->isTranslationUnit() &&
              !Reader.getContext().getLangOpts().CPlusPlus) {
-    IdentifierResolver &IdResolver = Reader.SemaObj->IdResolver;
+    IdentifierResolver &IdResolver = Reader.getIdResolver();
 
     // Temporarily consider the identifier to be up-to-date. We don't want to
     // cause additional lookups here.
-- 
2.40.0