[Bug target/118150] Failure to fold NOT+PTEST to NOTS for SVE

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118150

--- Comment #4 from Spencer Abson <sabson at gcc dot gnu.org> ---
For a similar reason, we're also missing BIC+PTEST under the same
conditions:

int
bar (svbool_t a, svbool_t b)
{
  svbool_t c = svptrue_b8();
  return svptest_first (c, svbic_z (c, a, b));
}

generates:

bar:
        ptrue   p3.b, all
        not     p0.b, p0/z, p1.b
        ptest   p3, p0.b
        cset    w0, first
        ret

instead of LLVM's

bar:
        ptrue   p2.b
        bics    p0.b, p2/z, p0.b, p1.b
        cset    w0, mi
        ret

Because predicated BIC is expanded into generic RTL as:

(and (and (not (b)) (a)) (c))   ; aarch64_pred_bicvnx16bi_z

And c is all-true, this can be reduced to the idiom for predicated
NOT (after cse1):

(and (not (b)) (a))             ; one_cmplvnx16bi3

For CC_NZC, it wouldn't be valid to fold the PTEST into a NOTS
here.