[PATCH v12 14/31] string: Improve generic strrchr with memrchr and strlen

[Richard Henderson]

On 2/2/23 08:11, Adhemerval Zanella wrote:
> Now that both strlen and memrchr have word vectorized implementation,
> it should be faster to implement strrchr based on memrchr over the
> string length instead of calling strchr on a loop.
> 
> Checked on x86_64-linux-gnu, i686-linux-gnu, powerpc-linux-gnu,
> and powerpc64-linux-gnu by removing the arch-specific assembly
> implementation and disabling multi-arch (it covers both LE and BE
> for 64 and 32 bits).
> ---
>   string/strrchr.c | 18 +-----------------
>   1 file changed, 1 insertion(+), 17 deletions(-)

memrchr needs libc_hidden_builtin_proto.  On riscv64:

    c:   00000097                auipc   ra,0x0
                         c: R_RISCV_CALL __GI_strlen
                         c: R_RISCV_RELAX        *ABS*
   10:   000080e7                jalr    ra # c <__GI_strrchr+0xc>
...
   24:   00000317                auipc   t1,0x0
                         24: R_RISCV_CALL_PLT    __memrchr
                         24: R_RISCV_RELAX       *ABS*
   28:   00030067                jr      t1 # 24 <.LVL2+0x8>


r~