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?
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
