Re: [PATCH 2/3] [APX CCMP] Adjust startegy for selecting ccmp candidates

[Hongyu Wang <wwwhhhyyy333@gmail.com>]

CC'd Richard for ccmp part as previously it is added only for aarch64.
The original logic will not interrupted since if
aarch64_gen_ccmp_first succeeded, aarch64_gen_ccmp_next will also
success, the cmp/fcmp and ccmp/fccmp supports all GPI/GPF, and the
prepare_operand will fixup the input that cmp supports but ccmp not,
so ret/ret2 will all be valid when comparing cost.
Thanks in advance.

Hongyu Wang <hongyu.wang@intel.com> 于2024年5月15日周三 16:22写道：
>
> For general ccmp scenario, the tree sequence is like
>
> _1 = (a < b)
> _2 = (c < d)
> _3 = _1 & _2
>
> current ccmp expanding will try to swap compare order for _1 and _2,
> compare the cost/cost2 between compare _1 and _2 first, then return the
> sequence with lower cost.
>
> For x86 ccmp, we don't support FP compare as ccmp operand, but we
> support fp comi + int ccmp sequence. With current cost comparison
> model, the fp comi + int ccmp can never be generated since it doesn't
> check whether expand_ccmp_next returns available result and the rtl
> cost for the empty ccmp sequence is always smaller.
>
> Check the expand_ccmp_next result ret and ret2, returns the valid one
> before cost comparison.
>
> gcc/ChangeLog:
>
>         * ccmp.cc (expand_ccmp_expr_1): Check ret and ret2 of
>         expand_ccmp_next, returns the valid one first before
>         comparing cost.
> ---
>  gcc/ccmp.cc | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/gcc/ccmp.cc b/gcc/ccmp.cc
> index 7cb525addf4..4b424220068 100644
> --- a/gcc/ccmp.cc
> +++ b/gcc/ccmp.cc
> @@ -247,7 +247,17 @@ expand_ccmp_expr_1 (gimple *g, rtx_insn **prep_seq, rtx_insn **gen_seq)
>               cost2 = seq_cost (prep_seq_2, speed_p);
>               cost2 += seq_cost (gen_seq_2, speed_p);
>             }
> -         if (cost2 < cost1)
> +
> +         /* For x86 target the ccmp does not support fp operands, but
> +            have fcomi insn that can produce eflags and then do int
> +            ccmp. So if one of the op is fp compare, ret1 or ret2 can
> +            fail, and the cost of the corresponding empty seq will
> +            always be smaller, then the NULL sequence will be returned.
> +            Add check for ret and ret2, returns the available one if
> +            the other is NULL.  */
> +         if ((!ret && ret2)
> +             || (!(ret && !ret2)
> +                 && cost2 < cost1))
>             {
>               *prep_seq = prep_seq_2;
>               *gen_seq = gen_seq_2;
> --
> 2.31.1
>