Hi!
On Wed, 2024-07-03 at 19:28 +0200, Sébastien Michelland wrote:
> On 2024-07-03 17:59, Jeff Law wrote:
> > On 7/3/24 3:59 AM, Sébastien Michelland wrote:
> > > libgcc's fp-bit.c is quite slow and most modern/developed architectures
> > > have switched to using the soft-fp library. This patch does so for
> > > free-standing/unknown-OS SH3/SH4 builds, using soft-fp's default
> > > parameters
> > > for the most part, most notably no exceptions.
> > >
> > > A quick run of Whetstone (built with OpenLibm) on an SH4 machine shows
> > > about x3 speedup (~320 -> 1050 Kwhets/s).
> > >
> > > I'm sending this as RFC because I'm quite unsure about testing. I built
> > > the compiler and ran the benchmark, but I don't know if GCC has a test
> > > for soft-fp correctness and whether I can run that in my non-hosted
> > > environment. Any advice?
> > >
> > > Cheers,
> > > Sébastien
> > >
> > > libgcc/ChangeLog:
> > >
> > > * config.host: Use soft-fp library for non-hosted SH3/SH4
> > > instead of fpdbit.
> > > * config/sh/sfp-machine.h: New.
> > I'd really like to hear from Oleg on this, though given we're using the
> > soft-fp library on other targets it seems reasonable at a high level.
I don't understand why this is being limited to SH3 and SH4 only?
Almost all SH4 systems out there have an FPU (unless special configurations
are used). So I'd say if switching to soft-fp, then for SH-anything, not
just SH3/SH4.
If it yields some improvements for some users, I'm all for it.
> > As far as testing, the GCC testsuite has some FP components which would
> > implicitly test soft fp on any target that doesn't have hardware
> > floating point.
>
> Thank you. I went this route, following the guide [1] and the
> instructions for cross-compiling [2] before hitting "Newlib does not
> support CPU sh3eb" which I should have seen coming.
>
> There are plenty of random ports lying around but just grabbing one
> doesn't feel right (and I don't have a canonical one to go to as I
> usually run a custom libc for... mostly bad reasons).
>
> Deferring maybe again to the few SH users... how do you usually do it?
>
>
I think it would make sense to test it using sh-sim on SH2 big-endian and
little endian at least, as that doesn't have an FPU and hence would run
tests utilizing soft-fp.
After building the toolchain for --target=sh-elf, you can use this to run
the testsuite in the simulator:
make -k check RUNTESTFLAGS="--target_board=sh-sim\{-m2/-ml,-m2/-mb}"
(add make -j parameter according to you needs -- it will be slow)
Let me know if you have any further questions.
Best regards,
Oleg Endo
