Hi Segher,
Thanks for the comments!
on 2022/7/22 02:48, Segher Boessenkool wrote:
> Hi!
>
> On Wed, Jul 20, 2022 at 05:31:11PM +0800, Kewen.Lin wrote:
>> As PR106345 shows, some test cases should be updated with
>> -mdejagnu-tune, since their test points are sensitive to
>> rs6000_tune, such as: group_ending_nop, loop align (ic),
>> float conversion cost etc.
>
> It does not make sense to require -mdejagnu-tune= if -mdejagnu-cpu= is
> already given? What is the failure case?
>
I think cpu setting only sets tune setting when tune setting isn't
explicitly provided as:
if (rs6000_tune_index >= 0)
tune_index = rs6000_tune_index;
else if (cpu_index >= 0)
rs6000_tune_index = tune_index = cpu_index;
As PR106345 shows, GCC can use an explicit tune setting when it's
configured, even if there is one "-mdejagnu-cpu=", it doesn't
override the explicit given one, so we need one explicit
"-mdejagnu-tune=".
One failure example is gcc.target/powerpc/loop_align.c
See function rs6000_loop_align:
/* Implement LOOP_ALIGN. */
align_flags
rs6000_loop_align (rtx label)
{
...
/* Align small loops to 32 bytes to fit in an icache sector, otherwise return
default. */
if (ninsns > 4 && ninsns <= 8
&& (rs6000_tune == PROCESSOR_POWER4
|| rs6000_tune == PROCESSOR_POWER5
|| rs6000_tune == PROCESSOR_POWER6
|| rs6000_tune == PROCESSOR_POWER7
|| rs6000_tune == PROCESSOR_POWER8))
return align_flags (5);
else
return align_loops;
Although the test case has adopted option "-mdejagnu-cpu=power7", but
the configured "--with-tune-64=power9" takes effect and make it
return align_loops instead of align_flags (5).
>> This patch is to replace -mdejagnu-cpu with -mdejagnu-tune
>> or append -mdejagnu-tune (keep the original -mdejagnu-cpu
>> when it's required) accordingly.
>
> It is *always* required. Testcases with -mtune= but unspecified -mcpu=
> make no sense.
>
The loop_align.c testings made me think if we know the insn count for
the loop on all cpus is in range (4,8] then the cpu setting doesn't matter.
I think I get your point, it's risky to assume that even if it works
for all existing cpus, will update with an explicit -mdejagnu-cpu here.
>> --- a/gcc/testsuite/gcc.target/powerpc/compress-float-ppc-pic.c
>> +++ b/gcc/testsuite/gcc.target/powerpc/compress-float-ppc-pic.c
>> @@ -1,5 +1,5 @@
>> /* { dg-do compile { target powerpc_fprs } } */
>> -/* { dg-options "-O2 -fpic -mdejagnu-cpu=power5" } */
>> +/* { dg-options "-O2 -fpic -mdejagnu-cpu=power5 -mdejagnu-tune=power5" } */
>> /* { dg-require-effective-target fpic } */
>
> This should only make a difference if you have -mtune= in your
> RUNTEST_FLAGS, and you shouldn't do silly things like that. I suspect
> you see it in other cases, and those are actual bugs then, that need
> actual fixing instead of sweeping under the carper.
>
Unfortunately it's due to the explicit tune setting in configuration.
> The testcase suggests this is with a compiler configured with
> --with-cpu= --with-tune=, which should just work, and -mcpu= should
> override both of those!
>
Unfortunately -mcpu= (-mdejagnu-cpu=) doesn't actually override here.
BR,
Kewen
