IR: Require DICompositeType for ODR uniquing type map

Tighten up the API for debug info ODR type uniquing in LLVMContext.  The
only reason to allow other DIType subclasses is to make the unit tests
prettier :/.

llvm-svn: 266737

llvm/lib/Bitcode/Reader/BitcodeReader.cpp

@@ -2192,12 +2192,12 @@ std::error_code BitcodeReader::parseMetadata(bool ModuleLevel) {
       // mapping.
       unsigned Flags = Record[10];
       auto *Identifier = getMDString(Record[15]);
-      DIType **MappedT = nullptr;
+      DICompositeType **MappedT = nullptr;
       if (!(Flags & DINode::FlagFwdDecl) && Identifier)
         MappedT = Context.getOrInsertODRUniquedType(*Identifier);
 
       // Use the mapped type node, or create a new one if necessary.
-      DIType *CT = MappedT ? *MappedT : nullptr;
+      DICompositeType *CT = MappedT ? *MappedT : nullptr;
       if (!CT) {
         CT = GET_OR_DISTINCT(
             DICompositeType, Record[0],