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

[Sebastian Huber <sebastian.huber@embedded-brains.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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