Assembling pending decls before writing their debug info

[Daniel Berlin]

On Wed, 2005-08-24 at 12:33 -0700, James E Wilson wrote:
> Nick Clifton wrote:
> >   The reason for this behaviour is that the debug information is being
> >   written out before the variables have been fully resolved.  In
> >   particular DECL_SET() for the second and third observer functions is
> >   NULL when the debug info is generated, which is why they are being
> >   given the DW_AT_const_value attribute.
> 
> See PR 21828 where some possible solutions for a related problem got
> discussed.  Eventually, PR 21828 was fixed when Richard Henderson fixed
> something else and Mark Mitchell's patch for PR 18556 got reverted.
> This is discussed in the log.
> 
> Meanwhile, there have been reports of some other related problems.
> There is a report from Apple near the end of PR 21828 that mentions
> stabs is still broken.  This got rereported as PR 23190 and contains a
> patch similar to ones discussed in PR 21828.
> 
> The interface between the front ends and cgraph really needs to be
> worked out here.  Currently, the C and C++ front ends are calling some
> cgraph functions in different orders, and we are having lots of debug
> related problems.
> 
> Maybe we need to move the calls to the debugging hooks from toplev into
> cgraph, so that they are only called when a variable is finalized? 

This is something i meant to do for 4.1, but didn't get to :(

At this point, cgraph should definitely be driving the debug output, at
least for the variables it knows about.
IMHO. :)

The blocker last time i looked was that we had to support
non-unit-at-a-time, and thus, it wasn't at all clear to me what logic i
could remove completely, and what logic needed to be !
flag_unit_at_a_time.