[Ada] Fix internal error on library-level type extended locally

[Eric Botcazou]

This is a regression present on the mainline, 10 and 9 branches: the compiler 
aborts on the local extension of a tagged type declared at library level, with 
a progenitor given by an interface type having a primitive that is a homograph 
of a primitive of the tagged type.

Tested on x86-64/Linux, applied on the mainline, 10 and 9 branches.


2020-12-07  Eric Botcazou  <ebotca...@adacore.com>

        * gcc-interface/trans.c (maybe_make_gnu_thunk): Return false if the
        target is local and thunk and target do not have the same context.

-- 
Eric Botcazou
diff --git a/gcc/ada/gcc-interface/trans.c b/gcc/ada/gcc-interface/trans.c
index bf8289ba323..4ab26d3e2dd 100644
--- a/gcc/ada/gcc-interface/trans.c
+++ b/gcc/ada/gcc-interface/trans.c
@@ -10730,8 +10730,11 @@ maybe_make_gnu_thunk (Entity_Id gnat_thunk, tree gnu_thunk)
 
   tree gnu_target = gnat_to_gnu_entity (gnat_target, NULL_TREE, false);
 
-  /* Thunk and target must have the same nesting level, if any.  */
-  gcc_assert (DECL_CONTEXT (gnu_thunk) == DECL_CONTEXT (gnu_target));
+  /* If the target is local, then thunk and target must have the same context
+     because cgraph_node::expand_thunk can only forward the static chain.  */
+  if (DECL_STATIC_CHAIN (gnu_target)
+      && DECL_CONTEXT (gnu_thunk) != DECL_CONTEXT (gnu_target))
+    return false;
 
   /* If the target returns by invisible reference and is external, apply the
      same transformation as Subprogram_Body_to_gnu here.  */