Re: [PATCH-for-10.2 v2 2/2] tcg/loongarch64: Support every TCGCond for cmp_vec ops

[Richard Henderson <richard.henderson@linaro.org>]

On 12/8/25 03:53, Philippe Mathieu-Daudé wrote:
> From: WANG Xuerui <git@xen0n.name>
> 
> Support for TCGCond's in loongarch64 cmp_vec codegen is not uniform: NE
> is not supported at all and will trip over assertions, and legalization
> (currently just operand-swapping) is not done for reg-imm comparisons.
> Since the TCG middle-end will not legalize the comparison conditions for
> us, we have to do it ourselves like other targets.
> 
> Because EQ/LT/LTU/LE/LEU are natively supported, we only have to keep
> the current operand swapping treatment for GT/GTU/GE/GEU but ensure it
> is done for both reg-reg and reg-imm cases, and use a bitwise NOT to
> help legalize NE.
> 
> Fixes: d8b6fa593d2d ("tcg/loongarch64: Lower cmp_vec to vseq/vsle/vslt")
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/3237
> Cc: Richard Henderson <richard.henderson@linaro.org>
> Cc: Philippe Mathieu-Daudé <philmd@linaro.org>
> Reported-by: Bingwu Zhang <xtexchooser@duck.com>
> Signed-off-by: WANG Xuerui <git@xen0n.name>
> Message-ID: <20251207055626.3685415-1-i.qemu@xen0n.name>
> [PMD: Split of bigger patch, part 2/2]
> Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
> ---
>   tcg/loongarch64/tcg-target.c.inc | 45 +++++++++++++++++++++++++-------
>   1 file changed, 35 insertions(+), 10 deletions(-)
> 
> diff --git a/tcg/loongarch64/tcg-target.c.inc b/tcg/loongarch64/tcg-target.c.inc
> index dbb36a2a816..1a243a57beb 100644
> --- a/tcg/loongarch64/tcg-target.c.inc
> +++ b/tcg/loongarch64/tcg-target.c.inc
> @@ -2184,6 +2184,33 @@ static void tcg_out_cmp_vec(TCGContext *s, bool lasx, unsigned vece,
>                               bool a2_is_const, TCGCond cond)
>   {
>       LoongArchInsn insn;
> +    bool need_invert = false;
> +
> +    switch (cond) {
> +    case TCG_COND_EQ:
> +    case TCG_COND_LE:
> +    case TCG_COND_LEU:
> +    case TCG_COND_LT:
> +    case TCG_COND_LTU:
> +        /* These are directly expressible. */
> +        break;
> +    case TCG_COND_NE:
> +        need_invert = true;
> +        cond = TCG_COND_EQ;
> +        break;
> +    case TCG_COND_GE:
> +    case TCG_COND_GEU:
> +    case TCG_COND_GT:
> +    case TCG_COND_GTU:
> +        {
> +            TCGArg t;
> +            t = a1, a1 = a2, a2 = t;
> +            cond = tcg_swap_cond(cond);
> +            break;
> +        }

To repeat my review of v1, you can't swap here if a2_is_const.


r~

> +    default:
> +        g_assert_not_reached();
> +    }
>   
>       static const LoongArchInsn cmp_vec_insn[16][2][4] = {
>           [TCG_COND_EQ] = {
> @@ -2236,32 +2263,30 @@ static void tcg_out_cmp_vec(TCGContext *s, bool lasx, unsigned vece,
>            * Try vseqi/vslei/vslti
>            */
>           int64_t value = sextract64(a2, 0, 8 << vece);
> +
> +        insn = cmp_vec_imm_insn[cond][lasx][vece];
>           switch (cond) {
>           case TCG_COND_EQ:
>           case TCG_COND_LE:
>           case TCG_COND_LT:
> -            insn = cmp_vec_imm_insn[cond][lasx][vece];
>               tcg_out32(s, encode_vdvjsk5_insn(insn, a0, a1, value));
>               break;
>           case TCG_COND_LEU:
>           case TCG_COND_LTU:
> -            insn = cmp_vec_imm_insn[cond][lasx][vece];
>               tcg_out32(s, encode_vdvjuk5_insn(insn, a0, a1, value));
>               break;
>           default:
>               g_assert_not_reached();
>           }
> +    } else {
> +        insn = cmp_vec_insn[cond][lasx][vece];
> +        tcg_out32(s, encode_vdvjvk_insn(insn, a0, a1, a2));
>       }
>   
> -    insn = cmp_vec_insn[cond][lasx][vece];
> -    if (insn == 0) {
> -        TCGArg t;
> -        t = a1, a1 = a2, a2 = t;
> -        cond = tcg_swap_cond(cond);
> -        insn = cmp_vec_insn[cond][lasx][vece];
> -        tcg_debug_assert(insn != 0);
> +    if (need_invert) {
> +        insn = lasx ? OPC_XVNOR_V : OPC_VNOR_V;
> +        tcg_out32(s, encode_vdvjvk_insn(insn, a0, a0, a0));
>       }
> -    tcg_out32(s, encode_vdvjvk_insn(insn, a0, a1, a2));
>   }
>   
>   static void tcg_out_vec_op(TCGContext *s, TCGOpcode opc,