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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/105180] [10/11/12/13 Regression] K&R style definition does
 not evaluate array size
Date: Wed, 11 Jan 2023 16:48:05 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D105180

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org,
                   |                            |jsm28 at gcc dot gnu.org

--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
int global =3D 0;

int
foo (void)
{
  ++global;
  return 1;
}

void
baz (void)
{
  void
  bar (s, c)
    char *s;
    char c[static foo ()];
  {
  }
  bar ("1", "1");
  bar ("1", "1");
  bar ("1", "1");
}

int
main ()
{
  baz ();
  if (global !=3D 3)
    __builtin_abort ();
  return 0;
}

shows that for nested functions those side-effects are emitted, but at a wr=
ong
location.
The side-effects in that case are evaluated when passing through the defini=
tion
of bar inside of the baz function,
rather than when bar is called.  So above, foo () is called just once, not 3
times.
If standard C declarations are used:
int global =3D 0;

int
foo (void)
{
  return ++global;
}

void
bar (char *s, char c[static foo ()])
{
}

int
main ()
{
  bar ("1", "1");
  if (global !=3D 1)
    __builtin_abort ();
  return 0;
}
then it works properly, in that case the pending sizes are recorded by
c_parser_parms_list_declarator -> push_parm_decl -> grokdeclarator and queu=
ed
by get_parm_info called from c_parser_parms_list_declarator.
But in case of K&R argument declarations, those are done by:
              while (c_parser_next_token_is_not (parser, CPP_EOF)
                     && c_parser_next_token_is_not (parser, CPP_OPEN_BRACE))
                c_parser_declaration_or_fndef (parser, false, false, false,
                                               true, false);
in c_parser_declaration_or_fndef and in that case that nested
c_parser_declaration_or_fndef calls start_decl which after
calling grokdeclarator which collects the pending expressions just does:
  if (expr)
    add_stmt (fold_convert (void_type_node, expr));
and so it is unclear where exactly it is pushed for the non-nested function=
s,
for nested ones at the current statement location (the definition of nested
function).
Bet we need to arrange for those side-effects to be instead remembered
somewhere and queued into pending_sizes later.=