[debug] Add -gdescribe-dies

This patch adds option -gdescribe-dies.  It sets the DW_AT_description
attribute of dies that do not get a DW_AT_name attribute, to make it easier
to figure out what the die is describing.

The option exports the names of artificial variables:
...
 DIE    0: DW_TAG_variable (0x7fa934dd54b0)
+  DW_AT_description: "D.1922"
   DW_AT_type: die -> 0 (0x7fa934dd0d70)
   DW_AT_artificial: 1

...
which can be traced back to gimple dumps:
...
  char a[0:D.1922] [value-expr: *a.0];
...

Furthermore, it adds names to external references:
...
 DIE    0: DW_TAG_subprogram (0x7fa88b9650f0)
+DW_AT_description: "main"
 DW_AT_abstract_origin: die -> label: vla_1.c.6719312a + 29 (0x7fa88b965140)
...
and likewise to DW_TAG_call_site_parameter DIEs.

Bootstrapped and reg-tested on x86_64.

2018-09-12  Tom de Vries  <tdevries@suse.de>

	* common.opt (gdescribe-dies): Add option.
	* dwarf2out.c (add_name_and_src_coords_attributes): Add description
	attribute for artifical and nameless decls.
	(dwarf2out_register_external_die): Add description attribute to
	external reference die.
	(add_desc_attribute): New functions.
	(gen_subprogram_die): Add description attribute to
	DW_TAG_call_site_parameter.
	* tree-pretty-print.c (print_generic_expr_to_str): New function.
	* tree-pretty-print.h (print_generic_expr_to_str): Declare.
	* doc/invoke.texi (@item Debugging Options): Add -gdescribe-dies and
	-gno-describe-dies.
	(@item -gdescribe-dies): Add.

From-SVN: r264229

gcc/ChangeLog

+2018-09-12  Tom de Vries  <tdevries@suse.de>
+
+	* common.opt (gdescribe-dies): Add option.
+	* dwarf2out.c (add_name_and_src_coords_attributes): Add description
+	attribute for artifical and nameless decls.
+	(dwarf2out_register_external_die): Add description attribute to
+	external reference die.
+	(add_desc_attribute): New functions.
+	(gen_subprogram_die): Add description attribute to
+	DW_TAG_call_site_parameter.
+	* tree-pretty-print.c (print_generic_expr_to_str): New function.
+	* tree-pretty-print.h (print_generic_expr_to_str): Declare.
+	* doc/invoke.texi (@item Debugging Options): Add -gdescribe-dies and
+	-gno-describe-dies.
+	(@item -gdescribe-dies): Add.
+
 2018-09-12  Aldy Hernandez  <aldyh@redhat.com>
 
 	* tree-vrp.c (vrp_shift_undefined_p): Remove.

gcc/common.opt

@@ -2976,6 +2976,10 @@ gstrict-dwarf
 Common Driver Report Var(dwarf_strict) Init(0)
 Don't emit DWARF additions beyond selected version.
 
+gdescribe-dies
+Common Driver Report Var(flag_describe_dies) Init(0)
+Add description attributes to some DWARF DIEs that have no name attribute.
+
 gtoggle
 Common Driver Report Var(flag_gtoggle)
 Toggle debug information generation.

gcc/doc/invoke.texi

@@ -373,7 +373,7 @@ Objective-C and Objective-C++ Dialects}.
 -ginternal-reset-location-views  -gno-internal-reset-location-views @gol
 -ginline-points  -gno-inline-points @gol
 -gvms  -gxcoff  -gxcoff+  -gz@r{[}=@var{type}@r{]} @gol
--gsplit-dwarf @gol
+-gsplit-dwarf -gdescribe-dies -gno-describe-dies @gol
 -fdebug-prefix-map=@var{old}=@var{new}  -fdebug-types-section @gol
 -fno-eliminate-unused-debug-types @gol
 -femit-struct-debug-baseonly  -femit-struct-debug-reduced @gol
@@ -7466,6 +7466,12 @@ the build system to avoid linking files with debug information.  To
 be useful, this option requires a debugger capable of reading @file{.dwo}
 files.
 
+@item -gdescribe-dies
+@opindex gdescribe-dies
+Add description attributes to some DWARF DIEs that have no name attribute,
+such as artificial variables, external references and call site
+parameter DIEs.
+
 @item -gpubnames
 @opindex gpubnames
 Generate DWARF @code{.debug_pubnames} and @code{.debug_pubtypes} sections.

gcc/dwarf2out.c

@@ -3816,6 +3816,7 @@ static bool add_location_or_const_value_attribute (dw_die_ref, tree, bool);
 static bool tree_add_const_value_attribute (dw_die_ref, tree);
 static bool tree_add_const_value_attribute_for_decl (dw_die_ref, tree);
 static void add_name_attribute (dw_die_ref, const char *);
+static void add_desc_attribute (dw_die_ref, tree);
 static void add_gnat_descriptive_type_attribute (dw_die_ref, tree, dw_die_ref);
 static void add_comp_dir_attribute (dw_die_ref);
 static void add_scalar_info (dw_die_ref, enum dwarf_attribute, tree, int,
@@ -6030,6 +6031,8 @@ dwarf2out_register_external_die (tree decl, const char *sym,
   else
     equate_decl_number_to_die (decl, die);
 
+  add_desc_attribute (die, decl);
+
   /* Add a reference to the DIE providing early debug at $sym + off.  */
   add_AT_external_die_ref (die, DW_AT_abstract_origin, sym, off);
 }
@@ -20536,6 +20539,52 @@ add_name_attribute (dw_die_ref die, const char *name_string)
     }
 }
 
+/* Generate a DW_AT_description attribute given some string value to be included
+   as the value of the attribute.  */
+
+static void
+add_desc_attribute (dw_die_ref die, const char *name_string)
+{
+  if (!flag_describe_dies || (dwarf_version < 3 && dwarf_strict))
+    return;
+
+  if (name_string == NULL || *name_string == 0)
+    return;
+
+  if (demangle_name_func)
+    name_string = (*demangle_name_func) (name_string);
+
+  add_AT_string (die, DW_AT_description, name_string);
+}
+
+/* Generate a DW_AT_description attribute given some decl to be included
+   as the value of the attribute.  */
+
+static void
+add_desc_attribute (dw_die_ref die, tree decl)
+{
+  tree decl_name;
+
+  if (!flag_describe_dies || (dwarf_version < 3 && dwarf_strict))
+    return;
+
+  if (decl == NULL_TREE || !DECL_P (decl))
+    return;
+  decl_name = DECL_NAME (decl);
+
+  if (decl_name != NULL && IDENTIFIER_POINTER (decl_name) != NULL)
+    {
+      const char *name = dwarf2_name (decl, 0);
+      add_desc_attribute (die, name ? name : IDENTIFIER_POINTER (decl_name));
+    }
+  else
+    {
+      char *desc = print_generic_expr_to_str (decl);
+      add_desc_attribute (die, desc);
+      free (desc);
+    }
+}
+
 /* Retrieve the descriptive type of TYPE, if any, make sure it has a
    DIE and attach a DW_AT_GNAT_descriptive_type attribute to the DIE
    of TYPE accordingly.
@@ -21294,12 +21343,17 @@ add_name_and_src_coords_attributes (dw_die_ref die, tree decl,
       const char *name = dwarf2_name (decl, 0);
       if (name)
 	add_name_attribute (die, name);
+      else
+	add_desc_attribute (die, decl);
+
       if (! DECL_ARTIFICIAL (decl))
 	add_src_coords_attributes (die, decl);
 
       if (!no_linkage_name)
 	add_linkage_name (die, decl);
     }
+  else
+    add_desc_attribute (die, decl);
 
 #ifdef VMS_DEBUGGING_INFO
   /* Get the function's name, as described by its RTL.  This may be different
@@ -23272,6 +23326,7 @@ gen_subprogram_die (tree decl, dw_die_ref context_die)
 	      dw_die_ref die = NULL;
 	      rtx tloc = NULL_RTX, tlocc = NULL_RTX;
 	      rtx arg, next_arg;
+	      tree arg_decl = NULL_TREE;
 
 	      for (arg = (ca_loc->call_arg_loc_note != NULL_RTX
 			  ? XEXP (ca_loc->call_arg_loc_note, 0)
@@ -23336,6 +23391,7 @@ gen_subprogram_die (tree decl, dw_die_ref context_die)
 		      tdie = lookup_decl_die (tdecl);
 		      if (tdie == NULL)
 			continue;
+		      arg_decl = tdecl;
 		    }
 		  else
 		    continue;
@@ -23352,6 +23408,7 @@ gen_subprogram_die (tree decl, dw_die_ref context_die)
 		    die = gen_call_site_die (decl, subr_die, ca_loc);
 		  cdie = new_die (dwarf_TAG (DW_TAG_call_site_parameter), die,
 				  NULL_TREE);
+		  add_desc_attribute (cdie, arg_decl);
 		  if (reg != NULL)
 		    add_AT_loc (cdie, DW_AT_location, reg);
 		  else if (tdie != NULL)

gcc/tree-pretty-print.c

@@ -162,6 +162,16 @@ print_generic_expr (FILE *file, tree t, dump_flags_t flags)
   pp_flush (tree_pp);
 }
 
+/* Print a single expression T to string, and return it.  */
+
+char *
+print_generic_expr_to_str (tree t)
+{
+  pretty_printer pp;
+  dump_generic_node (&pp, t, 0, TDF_VOPS|TDF_MEMSYMS, false);
+  return xstrdup (pp_formatted_text (&pp));
+}
+
 /* Dump NAME, an IDENTIFIER_POINTER, sanitized so that D<num> sequences
    in it are replaced with Dxxxx, as long as they are at the start or
    preceded by $ and at the end or followed by $.  See make_fancy_name

gcc/tree-pretty-print.h

@@ -38,6 +38,7 @@ extern void print_generic_decl (FILE *, tree, dump_flags_t);
 extern void print_generic_stmt (FILE *, tree, dump_flags_t = TDF_NONE);
 extern void print_generic_stmt_indented (FILE *, tree, dump_flags_t, int);
 extern void print_generic_expr (FILE *, tree, dump_flags_t = TDF_NONE);
+extern char *print_generic_expr_to_str (tree);
 extern void dump_omp_clauses (pretty_printer *, tree, int, dump_flags_t);
 extern int dump_generic_node (pretty_printer *, tree, int, dump_flags_t, bool);
 extern void print_declaration (pretty_printer *, tree, int, dump_flags_t);