Re: RFC: Variables in blocks of registers

[Daniel Berlin <dberlin at dberlin dot org>]

On Mon, 3 Feb 2003, Jim Blandy wrote:

>
> Andrew Cagney <ac131313@redhat.com> writes:
> > >> dwarf2 makes it possible to scatter a value across both memory and
> > >> registers.  It's been proposed that the `struct value' be augmented
> > >> with something like `struct location' that knows how to find any
> > >> sub component of a value.
> > > However, right now GCC doesn't generate this.  Probably because it
> > > would kill us.
> >
> > I'm not so sure.  In the past, GCC hasn't waited for GDB so I don't
> > think that would be the reason now.
>
> I thought it had.  A lot of the C++ stuff, for example;
> DW_AT_MIPS_linkage_name; etc.
>

Yup.
GCC has and does wait for GDB quite a bit, contrary to Andrew's assertion.
There have been times when people get frustrated enough to give up
waiting, it depends on the feature and the person who implemented it.
Generally, I wait indefinitely to commit, and complain a lot.
Others stew quietly, but give up waiting for GDB, and just commit it
without waiting for gdb to catch up.

If you'd rather me just do that, so you can consistently say
that gcc doesn't wait for gdb, i'll happily do so.

Just give me the word, and i'll go remove DW_AT_mips_linkage_name, for
instance.
It'll save a *large* amount of space in the C++ object files and binaries.

There's other pieces of code already committed that are waiting for gdb
too, a quick scan found this #if 0'd block in dwarf2out.c:

#if 0
      /* Disable this optimization for now; GDB wants to see two line notes
         at the beginning of a function so it can find the end of the
         prologue.  */

      /* Don't emit anything for redundant notes.  Just updating the
         address doesn't accomplish anything, because we already assume
         that anything after the last address is this line.  */
      if (line_info->dw_line_num == current_line
          && line_info->dw_file_num == current_file)
        continue;
#endif