When merging class definitions across modules in C++, merge together fields.

This change doesn't go all the way to making fields redeclarable; instead, it
makes them 'mergeable', which means we can find the canonical declaration, but
not much else (and for a declaration that's not from a module, the canonical
declaration is always that declaration).

llvm-svn: 192092

2 files changed, 38 insertions, 1 deletions

diff --git a/clang/lib/AST/Decl.cpp b/clang/lib/AST/Decl.cpp
index a0b3894a086..6ec14720007 100644
--- a/clang/lib/AST/Decl.cpp
+++ b/clang/lib/AST/Decl.cpp
@@ -34,6 +34,10 @@
 
 using namespace clang;
 
+Decl *clang::getPrimaryMergedDecl(Decl *D) {
+  return D->getASTContext().getPrimaryMergedDecl(D);
+}
+
 //===----------------------------------------------------------------------===//
 // NamedDecl Implementation
 //===----------------------------------------------------------------------===//
@@ -3094,6 +3098,10 @@ unsigned FieldDecl::getBitWidthValue(const ASTContext &Ctx) const {
 }
 
 unsigned FieldDecl::getFieldIndex() const {
+  const FieldDecl *Canonical = getCanonicalDecl();
+  if (Canonical != this)
+    return Canonical->getFieldIndex();
+
   if (CachedFieldIndex) return CachedFieldIndex - 1;
 
   unsigned Index = 0;
@@ -3101,7 +3109,7 @@ unsigned FieldDecl::getFieldIndex() const {
 
   for (RecordDecl::field_iterator I = RD->field_begin(), E = RD->field_end();
        I != E; ++I, ++Index)
-    I->CachedFieldIndex = Index + 1;
+    I->getCanonicalDecl()->CachedFieldIndex = Index + 1;
 
   assert(CachedFieldIndex && "failed to find field in parent");
   return CachedFieldIndex - 1;
diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp b/clang/lib/Serialization/ASTReaderDecl.cpp
index a5fb21cb66c..341f8eb068d 100644
--- a/clang/lib/Serialization/ASTReaderDecl.cpp
+++ b/clang/lib/Serialization/ASTReaderDecl.cpp
@@ -296,6 +296,9 @@ namespace clang {
     void mergeRedeclarable(Redeclarable<T> *D, T *Existing,
                            RedeclarableResult &Redecl);
 
+    template<typename T>
+    void mergeMergeable(Mergeable<T> *D);
+
     // FIXME: Reorder according to DeclNodes.td?
     void VisitObjCMethodDecl(ObjCMethodDecl *D);
     void VisitObjCContainerDecl(ObjCContainerDecl *D);
@@ -914,6 +917,7 @@ void ASTDeclReader::VisitFieldDecl(FieldDecl *FD) {
     if (FieldDecl *Tmpl = ReadDeclAs<FieldDecl>(Record, Idx))
       Reader.getContext().setInstantiatedFromUnnamedFieldDecl(FD, Tmpl);
   }
+  mergeMergeable(FD);
 }
 
 void ASTDeclReader::VisitMSPropertyDecl(MSPropertyDecl *PD) {
@@ -1874,6 +1878,22 @@ void ASTDeclReader::mergeRedeclarable(Redeclarable<T> *D, T *Existing,
   }
 }
 
+/// \brief Attempts to merge the given declaration (D) with another declaration
+/// of the same entity, for the case where the entity is not actually
+/// redeclarable. This happens, for instance, when merging the fields of
+/// identical class definitions from two different modules.
+template<typename T>
+void ASTDeclReader::mergeMergeable(Mergeable<T> *D) {
+  // If modules are not available, there is no reason to perform this merge.
+  if (!Reader.getContext().getLangOpts().Modules)
+    return;
+
+  if (FindExistingResult ExistingRes = findExisting(static_cast<T*>(D)))
+    if (T *Existing = ExistingRes)
+      Reader.Context.setPrimaryMergedDecl(static_cast<T*>(D),
+                                          Existing->getCanonicalDecl());
+}
+
 void ASTDeclReader::VisitOMPThreadPrivateDecl(OMPThreadPrivateDecl *D) {
   VisitDecl(D);
   unsigned NumVars = D->varlist_size();
@@ -2091,6 +2111,15 @@ static bool isSameEntity(NamedDecl *X, NamedDecl *Y) {
                                        TemplateY->getTemplateParameters());
   }
 
+  // Fields with the same name and the same type match.
+  if (FieldDecl *FDX = dyn_cast<FieldDecl>(X)) {
+    FieldDecl *FDY = cast<FieldDecl>(Y);
+    // FIXME: Diagnose if the types don't match. More generally, diagnose if we
+    // get a declaration in a class definition that isn't in the canonical class
+    // definition.
+    return X->getASTContext().hasSameType(FDX->getType(), FDY->getType());
+  }
+
   // FIXME: Many other cases to implement.
   return false;
 }