Debug Info: use DW_FORM_ref_addr instead of DW_FORM_ref4 if the referenced DIE
belongs to a different compile unit.

DW_FORM_ref_addr should be used for cross compile-unit reference.

When compiling a large application, we got a dwarfdump verification error where
abstract_origin points to nowhere.

This error can't be reproduced on any testing case in MultiSource.
We may have other cases where we use DW_FORM_ref4 unconditionally.

rdar://problem/13370501


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@176882 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/AsmPrinter/DwarfDebug.h b/lib/CodeGen/AsmPrinter/DwarfDebug.h
index 771bc36..81e345e 100644
--- a/lib/CodeGen/AsmPrinter/DwarfDebug.h
+++ b/lib/CodeGen/AsmPrinter/DwarfDebug.h
@@ -274,6 +274,10 @@
 
   /// \brief Returns the address pool.
   AddrPool *getAddrPool() { return &AddressPool; }
+
+  /// \brief for a given compile unit DIE, returns offset from beginning of
+  /// debug info.
+  unsigned getCUOffset(DIE *Die);
 };
 
 /// \brief Collects and handles dwarf debug information.