Re: [PATCH] tcg/i386: use 8-bit OR or XOR for unsigned 8-bit immediates

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

On 12/28/23 23:05, Paolo Bonzini wrote:
> In the case where OR or XOR has an 8-bit immediate between 128 and 255, we can
> operate on a low-byte register and shorten the output by two or three bytes
> (two if a prefix byte is needed for REX.B).
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>   tcg/i386/tcg-target.c.inc | 7 +++++++
>   1 file changed, 7 insertions(+)

Queued.  I adjusted the function a bit to use a switch.


r~

> 
> diff --git a/tcg/i386/tcg-target.c.inc b/tcg/i386/tcg-target.c.inc
> index 1791b959738..a24a23f43b1 100644
> --- a/tcg/i386/tcg-target.c.inc
> +++ b/tcg/i386/tcg-target.c.inc
> @@ -244,6 +244,7 @@ static bool tcg_target_const_match(int64_t val, TCGType type, int ct, int vece)
>   #define P_VEXL          0x80000         /* Set VEX.L = 1 */
>   #define P_EVEX          0x100000        /* Requires EVEX encoding */
>   
> +#define OPC_ARITH_EbIb	(0x80)
>   #define OPC_ARITH_EvIz	(0x81)
>   #define OPC_ARITH_EvIb	(0x83)
>   #define OPC_ARITH_GvEv	(0x03)		/* ... plus (ARITH_FOO << 3) */
> @@ -1366,6 +1367,12 @@ static void tgen_arithi(TCGContext *s, int c, int r0,
>           tcg_out8(s, val);
>           return;
>       }
> +    if (val == (uint8_t)val && (c == ARITH_OR || c == ARITH_XOR) &&
> +        (r0 < 4 || TCG_TARGET_REG_BITS == 64)) {
> +        tcg_out_modrm(s, OPC_ARITH_EbIb + P_REXB_RM, c, r0);
> +        tcg_out8(s, val);
> +        return;
> +    }
>       if (rexw == 0 || val == (int32_t)val) {
>           tcg_out_modrm(s, OPC_ARITH_EvIz + rexw, c, r0);
>           tcg_out32(s, val);