Debug Info: Use identifier to reference DIType in base type field of
ptr_to_member.

We introduce a new class DITypeRef that represents a reference to a DIType.
It wraps around a Value*, which can be either an identifier in MDString
or an actual MDNode. The class has a helper function "resolve" that
finds the actual MDNode for a given DITypeRef.

We specialize getFieldAs to return a field that is a reference to a
DIType. To correctly access the base type field of ptr_to_member,
getClassType now calls getFieldAs<DITypeRef> to return a DITypeRef.

Also add a typedef for DITypeIdentifierMap and a helper
generateDITypeIdentifierMap in DebugInfo.h. In DwarfDebug.cpp, we keep
a DITypeIdentifierMap and call generateDITypeIdentifierMap to actually
populate the map.

Verifier is updated accordingly.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@190081 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp b/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
index 4c95e14..6db54d2 100644
--- a/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
+++ b/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
@@ -905,7 +905,7 @@
 
   if (Tag == dwarf::DW_TAG_ptr_to_member_type)
       addDIEEntry(&Buffer, dwarf::DW_AT_containing_type, dwarf::DW_FORM_ref4,
-                  getOrCreateTypeDIE(DTy.getClassType()));
+                  getOrCreateTypeDIE(DD->resolve(DTy.getClassType())));
   // Add source line info if available and TyDesc is not a forward declaration.
   if (!DTy.isForwardDecl())
     addSourceLine(&Buffer, DTy);