Re: [PATCH v2 3/3] Add ffsl(), ffsll(), fls(), flsl(), flsll()

[Sebastian Huber <sebastian dot huber at embedded-brains dot de>]

On 27/07/17 03:40, Kito Cheng wrote:

> Hi
>
> I am testing with RISC-V with newlib/trunk and just hang on ffs,
> after investigate, I saw gcc just generate a ffs call in ffs for riscv64
> and I guess riscv64 is not the only target will hit this bug,
> so maybe we can revert the part of this patch, at least for ffs.c?
>
> Code gen by riscv64-elf-gcc:
>    .file "ffs.c"
>    .option nopic
>    .globl ffs
>    .text
>    .align 1
>    .globl ffs
>    .type ffs, @function
> ffs:
>    add sp,sp,-16
>    sd ra,8(sp)
>    call ffs
>    ld ra,8(sp)
>    sext.w a0,a0
>    add sp,sp,16
>    jr ra
>    .size ffs, .-ffs
>    .ident "GCC: (GNU) 8.0.0 20170509 (experimental)"

I get:

/build/git-build/b-gcc-git-riscv32-rtems4.12/./gcc/xgcc 
-B/build/git-build/b-gcc-git-riscv32-rtems4.12/./gcc/ -S -o - -O2 ffs.c 
-fno-builtin
        .file   "ffs.c"
        .option nopic
        .globl  __ffssi2
        .text
        .align  1
        .globl  ffs
        .type   ffs, @function
ffs:
        add     sp,sp,-16
        sw      ra,12(sp)
        call    __ffssi2
        lw      ra,12(sp)
        add     sp,sp,16
        jr      ra
        .size   ffs, .-ffs
        .ident  "GCC: (GNU) 8.0.0 20170727 (experimental)

Why does your GCC emit the call to ffs()?

> On Wed, Jul 5, 2017 at 7:26 PM, Corinna Vinschen <vinschen@redhat.com> wrote:
> > On Jul  5 10:54, Sebastian Huber wrote:
> > > Use compiler builtin for ffs().  Remove duplicate implementation from
> > > Cygwin.
> > >
> > > Signed-off-by: Sebastian Huber <sebastian.huber@embedded-brains.de>
> > > ---
> > >   newlib/libc/misc/ffs.c         | 14 ++-------
> > >   newlib/libc/string/Makefile.am |  5 ++++
> > >   newlib/libc/string/Makefile.in | 64 +++++++++++++++++++++++++++++++++---------
> > >   newlib/libc/string/ffsl.c      | 34 ++++++++++++++++++++++
> > >   newlib/libc/string/ffsll.c     | 34 ++++++++++++++++++++++
> > >   newlib/libc/string/fls.c       | 38 +++++++++++++++++++++++++
> > >   newlib/libc/string/flsl.c      | 38 +++++++++++++++++++++++++
> > >   newlib/libc/string/flsll.c     | 38 +++++++++++++++++++++++++
> > >   winsup/cygwin/syscalls.cc      | 22 ---------------
> > >   9 files changed, 240 insertions(+), 47 deletions(-)
> > >   create mode 100644 newlib/libc/string/ffsl.c
> > >   create mode 100644 newlib/libc/string/ffsll.c
> > >   create mode 100644 newlib/libc/string/fls.c
> > >   create mode 100644 newlib/libc/string/flsl.c
> > >   create mode 100644 newlib/libc/string/flsll.c
> > Patchset looks good, please push.
> >
> > For Cygwin we also need to add the new fls* entry points to
> > common.din and to the docs.  I'll do that later, when you
> > pushed your patch.
> >
> >
> > Thanks,
> > Corinna
> >
> > --
> > Corinna Vinschen
> > Cygwin Maintainer
> > Red Hat

--
Sebastian Huber, embedded brains GmbH

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