Basic ODR checking for C++ modules:

If we have multiple definitions of the same entity from different modules, we
nominate the first definition which we see as being the canonical definition.
If we load a declaration from a different definition and we can't find a
corresponding declaration in the canonical definition, issue a diagnostic.

This is insufficient to prevent things from going horribly wrong in all cases
-- we might be in the middle of emitting IR for a function when we trigger some
deserialization and discover that it refers to an incoherent piece of the AST,
by which point it's probably too late to bail out -- but we'll at least produce
a diagnostic.

llvm-svn: 192950

1 files changed, 12 insertions, 3 deletions

diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp b/clang/lib/Serialization/ASTReaderDecl.cpp
index 14379f31167..e68c7fc6f9f 100644
--- a/clang/lib/Serialization/ASTReaderDecl.cpp
+++ b/clang/lib/Serialization/ASTReaderDecl.cpp
@@ -2193,6 +2193,9 @@ ASTDeclReader::FindExistingResult ASTDeclReader::findExisting(NamedDecl *D) {
     return Result;
   }
 
+  // FIXME: Bail out for non-canonical declarations. We will have performed any
+  // necessary merging already.
+
   DeclContext *DC = D->getDeclContext()->getRedeclContext();
   if (DC->isTranslationUnit() && Reader.SemaObj) {
     IdentifierResolver &IdResolver = Reader.SemaObj->IdResolver;
@@ -2226,17 +2229,23 @@ ASTDeclReader::FindExistingResult ASTDeclReader::findExisting(NamedDecl *D) {
       if (isSameEntity(*I, D))
         return FindExistingResult(Reader, D, *I);
     }
-    return FindExistingResult(Reader, D, /*Existing=*/0);
   } else if (DeclContext *MergeDC = getPrimaryContextForMerging(DC)) {
     DeclContext::lookup_result R = MergeDC->noload_lookup(Name);
     for (DeclContext::lookup_iterator I = R.begin(), E = R.end(); I != E; ++I) {
       if (isSameEntity(*I, D))
         return FindExistingResult(Reader, D, *I);
     }
-    return FindExistingResult(Reader, D, /*Existing=*/0);
+  } else {
+    // Not in a mergeable context.
+    return FindExistingResult(Reader);
   }
 
-  return FindExistingResult(Reader);
+  // If this declaration is from a merged context, make a note that we need to
+  // check that the canonical definition of that context contains the decl.
+  if (Reader.MergedDeclContexts.count(D->getLexicalDeclContext()))
+    Reader.PendingOdrMergeChecks.push_back(D);
+
+  return FindExistingResult(Reader, D, /*Existing=*/0);
 }
 
 void ASTDeclReader::attachPreviousDecl(Decl *D, Decl *previous) {