[Bug target/59533] [SH] Missed cmp/pz opportunity

[olegendo at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59533

--- Comment #8 from Oleg Endo <olegendo at gcc dot gnu.org> ---
(In reply to Oleg Endo from comment #7)
> If a shll is followed by a cbranch:
> 
> unsigned int
> test_09_0 (int x, unsigned int y, unsigned int z)
> {
>   return ~(x >> 31) ? y : z;
> }
> 
>         shll    r4
>         bf      .L4
>         mov     r6,r5
> .L4:
>         rts
>         mov   r5,r0
> 
> it's better to use cmp/pz and invert the branch condition.
> Combine is looking for the following pattern:
> 

... however, if the result of the shll is used afterwards, it's better to keep
it.  For example triggered by this:


uint16_t crc16_ccitt(const uint8_t *buf, size_t size) {
    size_t i;
    uint32_t c, n;

    for(i = 0, n = 0; i < size; i++) {
        n ^= (buf[i] << 24);

        for(c = 0; c < 8; c++) {
            if(n & 0x80000000)
                n = (n << 1) ^ 0x10210000;
            else
                n = (n << 1);
        }
    }

    return n >> 16;
}