Re: [RFC PATCH 0/2] Add RISC-V vector math library support

On Thu, Feb 5, 2026, 3:53 AM Brian Inglis <[email protected]>
wrote:

> Benefits? - Performance? Accuracy? - numbers to back that up?
>

Are the vector extensions enabled by any multilib variant?

At least for RTEMS, we do not build single variant tool chains. Our risc-v
tool chain supports 32 and 64 variants. The OS source uses the compiler
predefines to tailor to which cpu variant is being compiled to. What
multilib variant would your configuration correspond to?

When did GCC start having the builtins used?

--joel
RTEMS

>
>
> On 2026-02-04 11:15, Pincheng Wang wrote:
> > This RFC patch series propose adding RISC-V Vector Extension (RVV)
> > optimized math functions to newlib, starting with a vectorized
> > implementation of sin().
> >
> > The motivation is to enable automatic vectorization of math functions on
> > RISC-V platforms with vector extensions, which can provide significant
> > performance improvements for numerical applications.
> >
> > After applying the gcc vecmath patch[1], compiler supports automatic
> > vectorzation using the vector ABI[2](also in RFC). When compiling with
> > auto-vectorization enabled (-O3 -ffast-math), the compiler can replace
> > scalar math function calls with vector variants if they are available in
> > the math library.
> >
> > This patch series adds infrastructure support for building vector math
> > functions conditionally via a newly added "--enable-vecmath" configure
> > option (disabled by default), and a vectorized sin() implementation for
> > RISC-V using intrinsics from the RISC-V Vector Extension.
> >
> > While adding the above option, I encountered an automake compatibility
> > issue during math object copying. Therefore, commit 1 is dedicated to
> > fixing that issue and does not involve any vector math changes.
> >
> > The vector sin implementation is derived from the SLEEF library (Boost
> > licensed) and adapted for newlib's RISC-V target. It uses RVV 1.0
> > intrinsics and provides performance-optimized computation with proper
> > handling of edge cases.
> >
> > To configure and build, use below command.
> >       configure --target=riscv64-unknown-elf \
> >               --prefix=/opt/vecmath-newlib \
> >               CFLAGS_FOR_TARGET="-O2 -march=rv64gcv -mabi=lp64d" \
> >               --enable-vecmath
> >
> > To compile a program that can take
> > benefit of this patch, use the patched[1] gcc and run command like
> > below.
> >       /opt/vecmath-gcc/bin/riscv64-unknown-elf-gcc \
> >               -O3 -ffast-math -march=rv64gcv \
> >               --sysroot=/opt/vecmath-newlib \
> >               -L/opt/vecmath-newlib/riscv64-unknown-elf/lib \
> >               -I/opt/vecmath-newlib/riscv64-unknown-elf/include \
> >               test_sin.c -o test_sin -lm
> >
> > Comments and suggestions are welcome!
> >
> > [1] https://gcc.gnu.org/pipermail/gcc-patches/2024-November/667352.html
> > [2] https://github.com/riscv-non-isa/riscv-elf-psabi-doc/pull/455
> >
> > Thanks,
> > Pincheng Wang
> >
> > Pincheng Wang (2):
> >    newlib: Fix automake 1.16 compatibility for math object copying
> >    newlib: Add RISC-V vector math library support
> >
> >   newlib/Makefile.am                         |   26 +-
> >   newlib/configure.ac                        |   10 +
> >   newlib/libc/include/math.h                 |    1 +
> >   newlib/libm/machine/riscv/Makefile.inc     |    5 +
> >   newlib/libm/machine/riscv/riscv-vec-math.h | 1461 ++++++++++++++++++++
> >   newlib/libm/machine/riscv/vec_sin.c        |   79 ++
> >   6 files changed, 1569 insertions(+), 13 deletions(-)
> >   create mode 100644 newlib/libm/machine/riscv/riscv-vec-math.h
> >   create mode 100644 newlib/libm/machine/riscv/vec_sin.c
> >
>
>
> --
> Take care. Thanks, Brian Inglis              Calgary, Alberta, Canada
>
> La perfection est atteinte                   Perfection is achieved
> non pas lorsqu'il n'y a plus rien à ajouter  not when there is no more to
> add
> mais lorsqu'il n'y a plus rien à retrancher  but when there is no more to
> cut
>                                  -- Antoine de Saint-Exupéry
>