[Bug target/88836] [SVE] Redundant PTEST in loop test

[kugan at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88836

--- Comment #2 from kugan at gcc dot gnu.org ---
Created attachment 45795
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=45795&action=edit
RFC patch

AFIK, we need to:
1. Change the whilelo pattern in backend
2. Change RTL CSE
- Add support for VEC_DUPLICATE
- When handling PARALLEL rtx, we  may kill CSE defined in the first set so that
it docent reach

Attached patch fix this. With the patch I now have:
.LFB0:
        .cfi_startproc
        cmp     w3, 0
        ble     .L1
        sub     w4, w3, #1
        cntw    x3
        lsr     w4, w4, 1
        add     w4, w4, 1
        whilelo p0.s, xzr, x4
        .p2align 3,,7
.L3:
        ld2w    {z4.s - z5.s}, p0/z, [x1]
        ld2w    {z2.s - z3.s}, p0/z, [x2]
        add     z0.s, z4.s, z2.s
        sub     z1.s, z5.s, z3.s
        st2w    {z0.s - z1.s}, p0, [x0]
        incb    x1, all, mul #2
        whilelo p0.s, x3, x4
        incb    x0, all, mul #2
        incw    x3
        incb    x2, all, mul #2
        bne     .L3
.L1:
        ret
        .cfi_endproc