Re: [PATCH] Skip constant folding for fmin/max when either argument is sNaN [PR105414]

["Kewen.Lin" <linkw@linux.ibm.com>]

on 2022/5/5 16:09, Richard Biener via Gcc-patches wrote:
> On Thu, May 5, 2022 at 10:07 AM HAO CHEN GUI via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
>>
>> Hi,
>>    This patch skips constant folding for fmin/max when either argument
>> is sNaN. According to C standard,
>>    fmin(sNaN, sNaN）= qNaN, fmin(sNaN, NaN) = qNaN
>>    So signaling NaN should be tested and skipped for fmin/max in match.pd.
>>
>>    Bootstrapped and tested on ppc64 Linux BE and LE with no regressions.
>> Is this okay for trunk? Any recommendations? Thanks a lot.
> 
> OK.
> 
> Thanks,
> Richard.
> 
>> ChangeLog
>>
>> 2022-05-05 Haochen Gui <guihaoc@linux.ibm.com>
>>
>> gcc/
>>         PR target/105414
>>         * match.pd (minmax): Skip constant folding for fmin/fmax when both
>>         arguments are sNaN or one is sNaN and another is NaN.
>>
>> gcc/testsuite/
>>         PR target/105414
>>         * gcc.dg/pr105414.c: New.
>>
>> patch.diff
>>
>> diff --git a/gcc/match.pd b/gcc/match.pd
>> index cad61848daa..f256bcbb483 100644
>> --- a/gcc/match.pd
>> +++ b/gcc/match.pd
>> @@ -3093,7 +3093,9 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
>>  (for minmax (min max FMIN_ALL FMAX_ALL)
>>   (simplify
>>    (minmax @0 @0)
>> -  @0))
>> +  /* if both are sNaN, it should return qNaN.  */
>> +  (if (!tree_expr_maybe_signaling_nan_p (@0))
>> +    @0)))

Sorry for chiming in.

IIUC this patch is mainly for libc function fmin/fmax and the iterator here
covers min/max and fmin/fmax.  I wonder if it's intent to make this change
for min/max as well?

As tree.def, "if either operand is NaN, then it is unspecified", the optimization
for min/max seems still acceptable?

BR,
Kewen