Re: [patch] const array types

[Pedro Alves <pedro@codesourcery.com>]

On Friday 24 September 2010 15:42:34, Joel Brobecker wrote:
> > I have filed now http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45765 as
> > I believe it could be fixed more at the DWARF producer side.
> 
> For what it's worth, I tend to agree that this should be fixed
> on the compiler side.

I disagree:

const struct { int x; } a;

struct S { int x; };
const struct S b;

It looks sane to me to not emit a whole new struct
type based on struct S that includes a
`const inst x' just for `b' (rather than DW_TAG_const_type
pointing at struct S).  Is `a' really any different?

> > I would find this patch OK even if it fixes only the TYPE_CODE_ARRAY.
> 
> I'm a little hesitant, still (but not objecting!). It it was a one-liner,
> I'd be less reluctant, but I just want to make sure that the improvement
> is worth the code we're adding. Yes, the output is more accurate, but
> is it really all that bad to be missing the `const'?

E.g., out of the blue, in C++ it can make the user call the
wrong function from gdb, when there are overloads
involved (, or templates, I guess):

$ cat const.cc
#include <stdio.h>

const struct { int x; } a = {0};

struct S { int x; };

const struct S b = {0};

__typeof__ (a.x) i1 = 0;
__typeof__ (b.x) i2 = 0;

void
function (int *f)
{
  printf ("called function (int *)\n");
}

void
function (const int *f)
{
  printf ("called function (const int *)\n");
}

int
main ()
{
  function (&a.x);
  function (&b.x);
  function (&i1);
  function (&i2);
}

$ ./gdb ./const 
...
(gdb) start
Temporary breakpoint 1 at 0x400638: file const.cc, line 27.
...
Temporary breakpoint 1, main () at const.cc:27
27        function (&a.x);

(gdb) call function(&a.x)
called function (int *)
^^^^^^^^^^^^^^^^^^^^^^^
(gdb) n
called function (const int *)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
28        function (&b.x);

-- 
Pedro Alves