DWARF5: Don't generate DW_AT_loclists_base for split compile unit DIEs.

The loclists_base attribute is used to point to the beginning of the
loclists index of a DWARF5 loclists table when using DW_FORM_loclistsx.
For split compile units the base is not given by the attribute, but is
either the first (and only) index in the .debug_loclists.dwo section,
or (when placed in a .dwp file) given by the DW_SECT_LOCLISTS row in
the .debug_cu_index section.

The loclists_base attribute is only valid for the full (or skeleton)
compile unit DIE in the main (relocatable) object. But GCC only ever
generates a loclists table index for the .debug_loclists section put
into the split DWARF .dwo file.

For split compile unit DIEs it is confusing (and not according to spec)
to also have a DW_AT_loclists_base attribute (which might be wrong,
since its relocatable offset won't actually be relocated).

gcc/ChangeLog

	* dwarf2out.c (dwarf2out_finish): Remove generation of
	DW_AT_loclists_base.

From-SVN: r261092

gcc/ChangeLog

+2018-06-01  Mark Wielaard  <mark@klomp.org>
+
+	* dwarf2out.c (dwarf2out_finish): Remove generation of
+	DW_AT_loclists_base.
+
 2018-06-01  Eric Botcazou  <ebotcazou@adacore.com>
 
 	* gimple-ssa-store-merging.c: Include gimple-fold.h.

gcc/dwarf2out.c

@@ -31297,9 +31297,15 @@ dwarf2out_finish (const char *)
     {
       if (have_location_lists)
 	{
-	  if (dwarf_version >= 5)
-	    add_AT_loclistsptr (comp_unit_die (), DW_AT_loclists_base,
-				loc_section_label);
+	  /* Since we generate the loclists in the split DWARF .dwo
+	     file itself, we don't need to generate a loclists_base
+	     attribute for the split compile unit DIE.  That attribute
+	     (and using relocatable sec_offset FORMs) isn't allowed
+	     for a split compile unit.  Only if the .debug_loclists
+	     section was in the main file, would we need to generate a
+	     loclists_base attribute here (for the full or skeleton
+	     unit DIE).  */
+
 	  /* optimize_location_lists calculates the size of the lists,
 	     so index them first, and assign indices to the entries.
 	     Although optimize_location_lists will remove entries from