Re: [RFC] Cleanup DW_CFA_GNU_args_size handling

[Jeff Law <law@redhat.com>]

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On 08/03/11 08:07, Georg-Johann Lay wrote:
> Georg-Johann Lay wrote:
>> Richard Henderson wrote:
>>> On 08/01/2011 11:42 AM, Georg-Johann Lay wrote:
>>>> Is there a specific reason not to define 
>>>> ACCUMULATE_OUTGOING_ARGS on AVR?
>>> Yes.  So that you can use PUSH.  But as I said in PR49881, you
>>> probably want to provide -maccumulate-outgoing-args.
>>> 
>>> I have a follow-up patch to the last one in that PR...
>>> 
>>> 
>>> r~
>> 
>> PUSH is fine but what about POP?
>> 
>> It's very expensive to pop several bytes, i.e. disabling IRQs,
>> loading and storing SP and the like. Usung store+displacement has
>> not this drawback and as I wrote, come code degradations you
>> explained in PR49881 are artifacts of PR46278, i.e. fake X
>> addressing.
>> 
>> Johann
>> 
> 
> Tried this test case:
> 
> #include <stdio.h>
> 
> void foo () { printf ("%d %d %d", 1, 2, 3); printf ("%d %d %d", 3, 4,
> 5); printf ("%d %d %d", 1, 4, 5); }
> 
> Attached the output: The compiler happily pushes onto the stack but
> pops only at the end of the function. So in a function with many such
> calls that would eat up great deal of RAM. It that what we want?
> 
> RETURN_POPS_ARGS cannot help here.
Popping arguments is deferred until the accumulated size of the deferred
argument pops reaches a particular threshold or certain other conditions
are met (see NO_DEFER_POP).

I don't recall the parameters used to determine when the accumulated
size is large enough to force pops, but I'm sure you can find it with a
little searching in the GCC sources.

Ahhh, memories of the m68k...

jeff
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