[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

1 files changed, 5 insertions, 0 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;
+}