Re: [PATCH] i386: Don't use VCOMX for XFmode compares

On Mon, Aug 10, 2026 at 9:03 AM Hu, Lin1 <[email protected]> wrote:
>
> Hi, all
>
> v{,u}comx insn only support DF/SF/HF mode, add extra mode checking during
> optimisation.
>
> Bootstrapped and regtested on x86-64-pc-linux, OK for trunk?
>
> BRs,
> Lin
>
> gcc/ChangeLog:
>
>         PR target/126676
>         * config/i386/i386-expand.cc (ix86_expand_fp_compare): Only use
>         UNSPEC_OPTCOMX for the modes VCOMX exists for.
>
> gcc/testsuite/ChangeLog:
>
>         PR target/126676
>         * gcc.target/i386/pr126676.c: New test.

LGTM.

Thanks,
Uros.

> ---
>  gcc/config/i386/i386-expand.cc           | 15 ++++++++-------
>  gcc/testsuite/gcc.target/i386/pr126676.c |  7 +++++++
>  2 files changed, 15 insertions(+), 7 deletions(-)
>  create mode 100644 gcc/testsuite/gcc.target/i386/pr126676.c
>
> diff --git a/gcc/config/i386/i386-expand.cc b/gcc/config/i386/i386-expand.cc
> index d0b92efc48b..fb4224af0da 100644
> --- a/gcc/config/i386/i386-expand.cc
> +++ b/gcc/config/i386/i386-expand.cc
> @@ -2922,6 +2922,7 @@ ix86_expand_fp_compare (enum rtx_code code, rtx op0, rtx op1)
>    rtx tmp, scratch;
>
>    code = ix86_prepare_fp_compare_args (code, &op0, &op1);
> +  machine_mode op_mode = GET_MODE (op0);
>
>    tmp = gen_rtx_COMPARE (CCFPmode, op0, op1);
>    if (unordered_compare)
> @@ -2932,14 +2933,14 @@ ix86_expand_fp_compare (enum rtx_code code, rtx op0, rtx op1)
>      {
>      case IX86_FPCMP_COMI:
>        tmp = gen_rtx_COMPARE (CCFPmode, op0, op1);
> +      /* VCOMX/VUCOMX only have DF/SF/HF mode instructions.  */
> +      if (TARGET_AVX10_2
> +         && (code == EQ || code == NE)
> +         && (op_mode == HFmode || op_mode == SFmode || op_mode == DFmode))
> +       tmp = gen_rtx_UNSPEC (CCFPmode, gen_rtvec (1, tmp), UNSPEC_OPTCOMX);
>        /* We only have vcomisbf16, No vcomubf16 nor vcomxbf16 */
> -      if (GET_MODE (op0) != E_BFmode)
> -       {
> -         if (TARGET_AVX10_2 && (code == EQ || code == NE))
> -           tmp = gen_rtx_UNSPEC (CCFPmode, gen_rtvec (1, tmp), UNSPEC_OPTCOMX);
> -         if (unordered_compare)
> -           tmp = gen_rtx_UNSPEC (CCFPmode, gen_rtvec (1, tmp), UNSPEC_NOTRAP);
> -       }
> +      if (op_mode != BFmode && unordered_compare)
> +       tmp = gen_rtx_UNSPEC (CCFPmode, gen_rtvec (1, tmp), UNSPEC_NOTRAP);
>        cmp_mode = CCFPmode;
>        emit_insn (gen_rtx_SET (gen_rtx_REG (CCFPmode, FLAGS_REG), tmp));
>        break;
> diff --git a/gcc/testsuite/gcc.target/i386/pr126676.c b/gcc/testsuite/gcc.target/i386/pr126676.c
> new file mode 100644
> index 00000000000..219a6133790
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/i386/pr126676.c
> @@ -0,0 +1,7 @@
> +/* { dg-do compile { target { ! ia32 } } } */
> +/* { dg-options "-O2 -march=x86-64 -mavx10.2 -mapxf" } */
> +/* { dg-final { scan-assembler-times "fucomip" 2 } } */
> +/* { dg-final { scan-assembler-not "comx" } } */
> +
> +int f1 (long double a, long double b, int x) { return x > 0 && a == b; }
> +int f2 (long double a, long double b, int x) { return x > 0 && a != b; }
> --
> 2.31.1
>