Re: [PATCH 17/18] target/i386/tcg: add a CCOp for SBB x,x

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

On 12/10/25 07:16, Paolo Bonzini wrote:
> This is more efficient both when generating code and when testing
> flags.

I guess sbb x,x appears quite frequently in x86 setcc computation, and the testing of the 
flags is much less important than the straight line code generation?


> diff --git a/target/i386/cpu.h b/target/i386/cpu.h
> index ecca38ed0b5..314e773a5d4 100644
> --- a/target/i386/cpu.h
> +++ b/target/i386/cpu.h
> @@ -1515,7 +1515,18 @@ typedef enum {
>       CC_OP_POPCNTL__,
>       CC_OP_POPCNTQ__,
>       CC_OP_POPCNT = sizeof(target_ulong) == 8 ? CC_OP_POPCNTQ__ : CC_OP_POPCNTL__,
> -#define CC_OP_LAST_BWLQ CC_OP_POPCNTQ__
> +
> +    /*
> +     * Note that only CC_OP_SBB_SELF (i.e. the one with MO_TL size)
> +     * is used or implemented, because the translation produces a
> +     * sign-extended CC_DST.
> +     */
> +    CC_OP_SBB_SELFB__, /* S/Z/C/A via CC_DST, O clear, P set.  */
> +    CC_OP_SBB_SELFW__,
> +    CC_OP_SBB_SELFL__,
> +    CC_OP_SBB_SELFQ__,
> +    CC_OP_SBB_SELF = sizeof(target_ulong) == 8 ? CC_OP_SBB_SELFQ__ : CC_OP_SBB_SELFL__,
> +#define CC_OP_LAST_BWLQ CC_OP_SBB_SELFQ__

The documentation here could be improved to note that CC_DST is always in {-1, 0}.  The 
fact that you can derive all other flags via masking less immediately relevant.

Otherwise,
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>


r~