On 07/03/2018 12:58 PM, Segher Boessenkool wrote:
> On Tue, Jul 03, 2018 at 12:15:48PM +0200, Martin Liška wrote:
>>> toplev.c already has (in init_alignments):
>>>
>>> if (align_jumps_max_skip > align_jumps)
>>> align_jumps_max_skip = align_jumps - 1;
>>
>> I'm rewriting this logic in the patch set. Issue is that
>> checking for value of align_jumps_max_skip is done
>> in rs6000_option_override_internal, which is place before
>> align_jumps_max_skip is parsed.
>>
>> That said, 'align_jumps_max_skip <= 0' is always true.
>
> It's not clear to me what you want me to do.
>
> You should write your patch so that the end result behaves the same as
> before, on all targets. If that requires changing (or at least checking)
> all targets, then you have a lot of work to do.
>
> If you think the rs6000 backend is doing something wrong, please say
> what exactly? I don't see it.
Uf, it's quite complicated I would say.
So first I believe for all -falign-{labels,loops,jumps} we don't handle properly
value of the argument. More precisely for a value of N (not power of 2),
we don't respect max_skip and we generate alignment to M, where M is first
bigger
power of 2 number. Example:
$ gcc /home/marxin/Programming/gcc/gcc/testsuite/gcc.dg/params/blocksort-part.c
-O2 -falign-labels=1025 -c -S -o /dev/stdout | grep align | sort | uniq -c
1 .align 32
132 .p2align 11
7 .p2align 4,,15
2^11 == 2048, but I would expect '.p2align 11,,1024' to be generated. That's
what you get for function alignment:
$ gcc /home/marxin/Programming/gcc/gcc/testsuite/gcc.dg/params/blocksort-part.c
-O2 -falign-functions=1025 -c -S -o /dev/stdout | grep align | sort | uniq -c
1 .align 32
7 .p2align 11,,1024
55 .p2align 3
48 .p2align 4,,10
Do I understand that correctly that it's broken?
On powerpc, because align_jumps_max_skip is set to 15, then we see
inconsistency like:
./xgcc -B.
/home/marxin/Programming/gcc/gcc/testsuite/gcc.dg/params/blocksort-part.c -O2
-falign-jumps=14 -c -S -o /dev/stdout | grep align | sort | uniq -c
...
27 .p2align 4,,13
...
which is correct.
but:
./xgcc -B.
/home/marxin/Programming/gcc/gcc/testsuite/gcc.dg/params/blocksort-part.c -O2
-falign-jumps=1025 -c -S -o /dev/stdout | grep align | sort | uniq -c
...
27 .p2align 11,,15
...
Here 11,,15 is completely broken value.
Martin
>
> Still confused,
>
>
> Segher
>
