Re: [PATCH 20/24] tcg/i386: Add cf parameter to tcg_out_cmp

[Peter Maydell]

On Tue, 8 Aug 2023 at 04:13, Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> Add the parameter to avoid TEST and pass along to tgen_arithi.
> All current users pass false.
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>  tcg/i386/tcg-target.c.inc | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/tcg/i386/tcg-target.c.inc b/tcg/i386/tcg-target.c.inc
> index b88fc14afd..56549ff2a0 100644
> --- a/tcg/i386/tcg-target.c.inc
> +++ b/tcg/i386/tcg-target.c.inc
> @@ -1418,15 +1418,15 @@ static void tcg_out_jxx(TCGContext *s, int opc, 
> TCGLabel *l, bool small)
>      }
>  }
>
> -static void tcg_out_cmp(TCGContext *s, TCGArg arg1, TCGArg arg2,
> -                        int const_arg2, int rexw)
> +static void tcg_out_cmp(TCGContext *s, int rexw, TCGArg arg1, TCGArg arg2,
> +                        int const_arg2, bool cf)
>  {
>      if (const_arg2) {
> -        if (arg2 == 0) {
> +        if (arg2 == 0 && !cf) {
>              /* test r, r */
>              tcg_out_modrm(s, OPC_TESTL + rexw, arg1, arg1);
>          } else {
> -            tgen_arithi(s, ARITH_CMP + rexw, arg1, arg2, 0);
> +            tgen_arithi(s, ARITH_CMP + rexw, arg1, arg2, cf);
>          }
>      } else {
>          tgen_arithr(s, ARITH_CMP + rexw, arg1, arg2);

I don't really understand the motivation here.
Why are some uses of this function fine with using the TEST
insn, but some must avoid it? What does 'cf' stand for?
A comment would help here if there isn't a clearer argument
name available...

thanks
-- PMM