[rs6000] Fix compare debug failure on AIX

[Tristan Gingold]

> On 04 May 2015, at 02:32, David Edelsohn <dje.gcc@gmail.com> wrote:
> 
> On Sat, May 2, 2015 at 6:04 AM, Eric Botcazou <ebotcazou@adacore.com> wrote:
>>> Why should GCC unnecessarily create stack frames to avoid
>>> compare-debug testcase failures?
>> 
>> I'm not sure I understand the question... compare-debug failures are failures
>> (-g is not supposed to change the generated code and this XCOFF-specific bug
>> was reported to us) so they need to be fixed.
>> 
>> From there on, as Alan said, there are 2 cases: either AIX needs a frame for
>> debugging or it doesn't.  If the latter, then the lines can simply be deleted.
>> If the former, we have to draw a line somewhere; Alan suggests always creating
>> a frame while I suggest creating it only at -O0 and -Og.
> 
> I believe that AIX does need a frame for debugging.  I don't remember
> the exact reason off hand.
> 
> I'm sorry that XCOFF debugging changes the generated code (only in the
> sense of allocating a frame), but that is a system dependency.  It's
> been this way for over 20 years.  I see no reason to produce worse
> code at -O0 when not debugging simply to make testcases happier.
> 
> By the way, I'm still waiting for the DWARF debugging patches from
> Adacore compatible with AIX as and ld.  DWARF debugging would not
> require pushing a frame, and would resolve the failure when testing
> with DWARF.  The patch would be adjusted to only push a frame when
> writing XCOFF debugging.

Sorry but we don’t have these patches.  We have a tiny patch to generate
Dwarf debug infos on XCOFF platforms but that requires GNU as and ld.

Tristan.