[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.

llvm-svn: 268817

2 files changed, 9 insertions, 5 deletions

diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
index e33cccbd95c..5d459ac9fb6 100644
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/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/clang/lib/Serialization/ASTReaderDecl.cpp b/clang/lib/Serialization/ASTReaderDecl.cpp
index a6e993885a7..1a013cee219 100644
--- a/clang/lib/Serialization/ASTReaderDecl.cpp
+++ b/clang/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.