DWARF: do not emit DW_TAG_variable to materialize DWARF procedures

Hello,

For -gdwarf-3 and newer, the DWARF back-end sometimes generates DWARF
procedures to factorize complex location descriptions.  DWARF procedures
can be materialized as DW_TAG_dwarf_procedure DIEs, but actually any DIE
that can hold a DW_AT_location attribute is also accepted.

Unlike what I thought at some point, the DW_TAG_dwarf_procedure tag was
introduced in the DWARFv3 standard, not the DWARFv4 one, so the back-end
can always emit DW_TAG_dwarf_procedure DIEs, as this simplifies code and
prevents the types pruning pass from missing a DWARF procedure.

Boostrapped and regtested on x86_64-linux: no regression.  Ok to commit?
Thank you in advance!

gcc/

	* dwarf2out.c (copy_dwarf_procedure): Remove obsolete comment.
	(new_dwarf_proc_die): Emit DW_TAG_dwarf_procedure DIEs even for
	-gdwarf-3.
	(function_to_dwarf_procedure): Update comment.

From-SVN: r239575

gcc/ChangeLog

+2016-08-18  Pierre-Marie de Rodat  <derodat@adacore.com>
+
+	* dwarf2out.c (copy_dwarf_procedure): Remove obsolete comment.
+	(new_dwarf_proc_die): Emit DW_TAG_dwarf_procedure DIEs even for
+	-gdwarf-3.
+	(function_to_dwarf_procedure): Update comment.
+
 2016-08-18  David Malcolm  <dmalcolm@redhat.com>
 
 	* input.c (diagnostics_file_cache_forcibly_evict_file): New

gcc/dwarf2out.c

@@ -7747,9 +7747,6 @@ copy_dwarf_procedure (dw_die_ref die,
 		      comdat_type_node *type_node,
 		      hash_map<dw_die_ref, dw_die_ref> &copied_dwarf_procs)
 {
-  /* We do this for COMDAT section, which is DWARFv4 specific, so
-     DWARF procedure are always DW_TAG_dwarf_procedure DIEs (unlike
-     DW_TAG_variable in DWARFv3).  */
   gcc_assert (die->die_tag == DW_TAG_dwarf_procedure);
 
   /* DWARF procedures are not supposed to have children...  */
@@ -15332,22 +15329,15 @@ static dw_die_ref
 new_dwarf_proc_die (dw_loc_descr_ref location, tree fndecl,
 		    dw_die_ref parent_die)
 {
-  const bool dwarf_proc_supported = dwarf_version >= 4;
   dw_die_ref dwarf_proc_die;
 
   if ((dwarf_version < 3 && dwarf_strict)
       || location == NULL)
     return NULL;
 
-  dwarf_proc_die  = new_die (dwarf_proc_supported
-			     ? DW_TAG_dwarf_procedure
-			     : DW_TAG_variable,
-			     parent_die,
-			     fndecl);
+  dwarf_proc_die = new_die (DW_TAG_dwarf_procedure, parent_die, fndecl);
   if (fndecl)
     equate_decl_number_to_die (fndecl, dwarf_proc_die);
-  if (!dwarf_proc_supported)
-    add_AT_flag (dwarf_proc_die, DW_AT_artificial, 1);
   add_AT_loc (dwarf_proc_die, DW_AT_location, location);
   return dwarf_proc_die;
 }
@@ -15673,9 +15663,7 @@ function_to_dwarf_procedure (tree fndecl)
   if (dwarf_proc_die != NULL)
     return dwarf_proc_die;
 
-  /* DWARF procedures are available starting with the DWARFv3 standard, but
-     it's the DWARFv4 standard that introduces the DW_TAG_dwarf_procedure
-     DIE.  */
+  /* DWARF procedures are available starting with the DWARFv3 standard.  */
   if (dwarf_version < 3 && dwarf_strict)
     return NULL;