> Am 31.05.2024 um 20:56 schrieb Georg-Johann Lay <a...@gjlay.de>:
>
>
>
> Am 31.05.24 um 19:32 schrieb Richard Biener:
>>>> Am 31.05.2024 um 17:25 schrieb Paul Koning via Gcc <gcc@gcc.gnu.org>:
>>>
>>>
>>>
>>>> On May 31, 2024, at 11:06 AM, Georg-Johann Lay <a...@gjlay.de> wrote:
>>>>
>>>>
>>>>
>>>> Am 31.05.24 um 17:00 schrieb Paul Koning:
>>>>>>> On May 31, 2024, at 9:52 AM, Georg-Johann Lay <a...@gjlay.de> wrote:
>>>>>>>
>>>>>>> What's the recommended way to stop built-in expansions in gcc?
>>>>>>>
>>>>>>> For example, avr-gcc expands isinff() to a bloated version of an
>>>>>>> isinff() implementation that's written in asm (PR115307).
>>>>>>>
>>>>>>> Johann
>>>>> Isn't that up to the target back end?
>>>>> paul
>>>>
>>>>
>>>> Yes, that's the reason why it's a target PR.
>>>>
>>>> My question is where/how to do it.
>>>>
>>>> It's clear that twiddling the options works and is a simple and
>>>> comprehensible solution, but it seems a bit of a hack to me.
>>>>
>>>> Johann
>>>
>>> I haven't dug deep into this, but I would think at least part of the answer
>>> is in the target cost functions. If those assign RTX cost according to
>>> size, then the result would be the optimizer would favor smaller code.
>>> Right?
>>>
>>> Does inline assembly expansion of builtins depend on target code supplying
>>> that expansion? If so, the answer would be not to supply it, or at least
>>> not unless asked for by an option. If it comes from common code, that's a
>>> different matter, then perhaps there should be target hooks to let the
>>> target disallow or discourage such expansion. I might want such a thing
>>> for pdp11 as well.
>> The function in question is folded to a comparison very early if the target
>> does not implement an optab for it. After that everything is lost. A
>> workaround is to define an optab but let expansion always FAIL.
>> Richard
>
> You have a pointer how to define a target optab? I looked into optabs code
> but found no appropriate hook. For isinf<mode> is seems is is enough to
> provide a failing expander, but other functions like isnan don't have an
> optab entry, so there is a hook mechanism to extend optabs?
Just add corresponding optabs for the missing cases (some additions are
pending, like isnornal). There’s no hook to prevent folding to FP compares nor
is that guarded by other means (like availability of native FP ops). Changing
the guards would be another reasonable option.
Richard
> I also looked into patching options, but there is no way to hook in, or at
> least I did not find how to use targetm.handle_option or an appropriate place
> to call disable_builtin_function; it's all baken into the C front without any
> hook opportunity.
>
> Johann
>
>
