Re: [PATCH v2 2/4] LoongArch: Add ftint{,rm,rp}.{w,l}.{s,d} instructions

[Lulu Cheng <chenglulu@loongson.cn>]

I have no more questions.

Thanks.

在 2022/11/11 下午1:29, Xi Ruoyao 写道:
> Lulu:
>
> So I think the code is correct:
>
> +   (<lrint_allow_inexact>
> +    || flag_fp_int_builtin_inexact
> +    || !flag_trapping_math)"
>
> <lrint_allow_inexact> is 1 for lrint, 0 for lceil and lfloor.  As N3054
> says:
>
>     The lrint and llrint functions provide floating-to-integer conversion as prescribed by IEC 60559.
>     They round according to the current rounding direction. If the rounded value is outside the range of
>     the return type, the numeric result is unspecified and the "invalid" floating-point exception is raised.
>     When they raise no other floating-point exception and the result differs from the argument, they
>     raise the "inexact" floating-point exception.
>     
> If flag_fp_int_builtin_inexact is set, we allow lceil and lfloor to
> raise "inexact".
>
> If flag_trapping_math is not set (it's set by default and can only be
> unset explicitly with -fno-trapping-math: it's not even implied by -
> ffast-math), we don't care about whether exceptions are raised or not.
>
> So lceil and lfloor can be used if -ffp-int-builtin-inexact, or -fno-
> trapping-math.
>
> On Fri, 2022-11-11 at 00:07 +0000, Joseph Myers wrote:
>> On Thu, 10 Nov 2022, Xi Ruoyao via Gcc-patches wrote:
>>
>>> Joseph: can you confirm that -ftrapping-math allows floor and ceil to
>>> raise inexact exception?  The man page currently says:
>>>
>>> The default is -ffp-int-builtin-inexact, allowing the exception to be
>>> raised, unless C2X or a later C standard is selected.  This option does
>>>                                                         ^^^^^^^^^^^
>>> nothing unless -ftrapping-math is in effect.
>>>
>>> To me it's not very clear that "this option" stands for -fno-fp-int-
>>> builtin-inexact or -ffp-int-builtin-inexact.
>> The -ftrapping-math option (which is on by default) means that we care
>> about whether operations raise exceptions: they should raise exceptions if
>> and only if the relevant standard permit them to do so.
>>
>> The combination of -ftrapping-math with -fno-fp-int-builtin-inexact means
>> the listed built-in functions must not raise "inexact".
>>
>> If -fno-trapping-math is used, then we don't care about whether exceptions
>> are raised or not (for any floating-point operations, not just those
>> functions).  So given -fno-trapping-math, there is no difference between
>> -fno-fp-int-builtin-inexact and -ffp-int-builtin-inexact.
>>
>> If -ffp-int-builtin-inexact (default before C2X), we don't care about
>> whether those functions raise "inexact" (but still care about other
>> exceptions and exceptions for other operations, unless
>> -fno-trapping-math).