[PATCH] debug: Improve debug info of c++14 deduced return type [PR94459]

[Jakub Jelinek <jakub@redhat.com>]

Hi!

On the following testcase, in gdb ptype S<long>::m1 prints long as return
type, but all the other methods show void instead.
PR53756 added code to add_type_attribute if the return type is
auto/decltype(auto), but we actually should look through references,
pointers and qualifiers.
Haven't included there DW_TAG_atomic_type, because I think at least ATM
one can't use that in C++.  Not sure about DW_TAG_array_type or what else
could be deduced.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

2020-04-04  Domani Hannes  <ssbssa@yahoo.de>
	    Jakub Jelinek  <jakub@redhat.com>

	PR debug/94459
	* dwarf2out.c (gen_subprogram_die): Look through references, pointers
	and qualifiers when checking if in-class DIE had an 'auto' or
	'decltype(auto)' return type to emit type again on definition.

	* g++.dg/debug/pr94459.C: New test.

--- gcc/dwarf2out.c.jj	2020-04-03 10:04:44.704972108 +0200
+++ gcc/dwarf2out.c	2020-04-03 17:52:48.909483818 +0200
@@ -22905,11 +22905,19 @@ gen_subprogram_die (tree decl, dw_die_re
 		  != (unsigned) s.column))
 	    add_AT_unsigned (subr_die, DW_AT_decl_column, s.column);
 
-	  /* If the prototype had an 'auto' or 'decltype(auto)' return type,
+	  /* If the prototype had a cv 'auto' or 'decltype(auto)' return type,
 	     emit the real type on the definition die.  */
 	  if (is_cxx () && debug_info_level > DINFO_LEVEL_TERSE)
 	    {
 	      dw_die_ref die = get_AT_ref (old_die, DW_AT_type);
+	      while (die
+		     && (die->die_tag == DW_TAG_reference_type
+			 || die->die_tag == DW_TAG_rvalue_reference_type
+			 || die->die_tag == DW_TAG_pointer_type
+			 || die->die_tag == DW_TAG_const_type
+			 || die->die_tag == DW_TAG_volatile_type
+			 || die->die_tag == DW_TAG_restrict_type))
+		die = get_AT_ref (die, DW_AT_type);
 	      if (die == auto_die || die == decltype_auto_die)
 		add_type_attribute (subr_die, TREE_TYPE (TREE_TYPE (decl)),
 				    TYPE_UNQUALIFIED, false, context_die);
--- gcc/testsuite/g++.dg/debug/pr94459.C.jj	2020-04-03 18:06:28.234725520 +0200
+++ gcc/testsuite/g++.dg/debug/pr94459.C	2020-04-03 18:05:59.287104932 +0200
@@ -0,0 +1,49 @@
+// PR debug/94459
+// { dg-do compile { target c++11 } }
+// { dg-options "-g -dA" }
+
+template <typename T>
+struct S
+{
+  T v;
+  S () : v (0) {}
+  auto m1 () { return v; }
+  auto &m2 () { return v; }
+  auto &&m3 () { return (T&&)v; }
+  const auto m4 () { return v; }
+  const auto &m5 () { return v; }
+  const auto &&m6 () { return (T&&)v; }
+  volatile auto m7 () { return v; }
+  volatile auto &m8 () { return v; }
+  volatile auto &&m9 () { return (T&&)v; }
+  volatile const auto m10 () { return v; }
+  volatile const auto &m11 () { return v; }
+  volatile const auto &&m12 () { return (T&&)v; }
+  const volatile auto m13 () { return v; }
+  const volatile auto &m14 () { return v; }
+  const volatile auto &&m15 () { return (T&&)v; }
+#ifndef __STRICT_ANSI__
+  __restrict const volatile auto &&m16 () { return (T&&)v; }
+  const __restrict auto &m17 () { return v; }
+#endif
+};
+
+S<long> s, u, v;
+
+long
+foo ()
+{
+  return s.m1 () + s.m2 () + s.m3 () + s.m4 () + s.m5 ()
+	 + s.m6 () + s.m7 () + s.m8 () + s.m9 () + s.m10 ()
+	 + s.m11 () + s.m12 () + s.m13 () + s.m14 () + s.m15 ()
+#ifndef __STRICT_ANSI__
+	 + u.m16 () + v.m17 ()
+#endif
+	 + 0;
+}
+
+int
+main ()
+{
+  return foo ();
+}

	Jakub