debug/107058 - gracefully handle unexpected DIE contexts

While the bug is persisting that LTO streaming picks up a CONST_DECL
from an attribute argument on a VAR_DECL which with -fdebug-type-section
refers to a DIE in a type unit we can handle this gracefully, at least
with -fno-checking.  Do so.  The C++ frontend nevetheless should resolve
the CONST_DECL attribute argument to a constant.

	PR debug/107058
	* dwarf2out.cc (dwarf2out_die_ref_for_decl): Gracefully
	handle unexpected but bogus DIE contexts when not checking
	enabled.

	* c-c++-common/pr107058.c: New testcase.

1 files changed, 11 insertions, 4 deletions

diff --git a/gcc/dwarf2out.cc b/gcc/dwarf2out.cc
index 0b8a300..2b72321 100644
--- a/gcc/dwarf2out.cc
+++ b/gcc/dwarf2out.cc
@@ -6061,10 +6061,17 @@ dwarf2out_die_ref_for_decl (tree decl, const char **sym,
     die = die->die_parent;
   /* For the containing CU DIE we compute a die_symbol in
      compute_comp_unit_symbol.  */
-  gcc_assert (die->die_tag == DW_TAG_compile_unit
-	      && die->die_id.die_symbol != NULL);
-  *sym = die->die_id.die_symbol;
-  return true;
+  if (die->die_tag == DW_TAG_compile_unit)
+    {
+      gcc_assert (die->die_id.die_symbol != NULL);
+      *sym = die->die_id.die_symbol;
+      return true;
+    }
+  /* While we can gracefully handle running into say a type unit
+     we don't really want and consider this a bug.  */
+  if (flag_checking)
+    gcc_unreachable ();
+  return false;
 }
 
 /* Add a reference of kind ATTR_KIND to a DIE at SYMBOL + OFFSET to DIE.  */