Move the initialization of VAListTagName after InitializeSema()

This innocuous statement to get the identifier info for __va_list_tag
was causing an assertion failure:
  NextIsPrevious() && "decl became non-canonical unexpectedly"
if the __va_list_tag identifier was found in a PCH in some
circumstances, because it was looked up before the ASTReader had a Sema
object to use to find existing decls to merge with.

We could possibly move getting the identifier info even later, or make
it lazy if we wanted to, but this seemed like the minimal change.

Now why a PCH would have this identifier in the first place is a bit
mysterious. This seems to be related to the global module index in some
way, because when the test case is built without the global module index
it will not emit an identifier for __va_list_tag into the PCH, but with
the global module index it does.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@217275 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 4 insertions, 2 deletions

diff --git a/lib/Sema/Sema.cpp b/lib/Sema/Sema.cpp
index 205081b656..c762d5fdac 100644
--- a/lib/Sema/Sema.cpp
+++ b/lib/Sema/Sema.cpp
@@ -69,8 +69,6 @@ PrintingPolicy Sema::getPrintingPolicy(const ASTContext &Context,
 void Sema::ActOnTranslationUnitScope(Scope *S) {
   TUScope = S;
   PushDeclContext(S, Context.getTranslationUnitDecl());
-
-  VAListTagName = PP.getIdentifierInfo("__va_list_tag");
 }
 
 Sema::Sema(Preprocessor &pp, ASTContext &ctxt, ASTConsumer &consumer,
@@ -155,6 +153,10 @@ void Sema::Initialize() {
       = dyn_cast_or_null<ExternalSemaSource>(Context.getExternalSource()))
     ExternalSema->InitializeSema(*this);
 
+  // This needs to happen after ExternalSemaSource::InitializeSema(this) or we
+  // will not be able to merge any duplicate __va_list_tag decls correctly.
+  VAListTagName = PP.getIdentifierInfo("__va_list_tag");
+
   // Initialize predefined 128-bit integer types, if needed.
   if (Context.getTargetInfo().hasInt128Type()) {
     // If either of the 128-bit integer types are unavailable to name lookup,