Re: [PATCH v2 01/10] accel/tcg: Reduce CF_COUNT_MASK to match TCG_MAX_INSNS

[Peter Maydell]

On Mon, 12 Jul 2021 at 16:42, Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> The space reserved for CF_COUNT_MASK was overly large.
> Reduce to free up cflags bits and eliminate an extra test.
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>  include/exec/exec-all.h   | 4 +++-
>  accel/tcg/translate-all.c | 5 ++---
>  2 files changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/include/exec/exec-all.h b/include/exec/exec-all.h
> index 754f4130c9..dfe82ed19c 100644
> --- a/include/exec/exec-all.h
> +++ b/include/exec/exec-all.h
> @@ -492,7 +492,9 @@ struct TranslationBlock {
>      target_ulong cs_base; /* CS base for this block */
>      uint32_t flags; /* flags defining in which context the code was 
> generated */
>      uint32_t cflags;    /* compile flags */
> -#define CF_COUNT_MASK  0x00007fff
> +
> +/* Note that TCG_MAX_INSNS is 512; we validate this match elsewhere. */
> +#define CF_COUNT_MASK  0x000001ff
>  #define CF_LAST_IO     0x00008000 /* Last insn may be an IO access.  */
>  #define CF_MEMI_ONLY   0x00010000 /* Only instrument memory ops */
>  #define CF_USE_ICOUNT  0x00020000
> diff --git a/accel/tcg/translate-all.c b/accel/tcg/translate-all.c
> index 4df26de858..997e44c73b 100644
> --- a/accel/tcg/translate-all.c
> +++ b/accel/tcg/translate-all.c
> @@ -1430,9 +1430,8 @@ TranslationBlock *tb_gen_code(CPUState *cpu,
>      if (max_insns == 0) {
>          max_insns = CF_COUNT_MASK;
>      }
> -    if (max_insns > TCG_MAX_INSNS) {
> -        max_insns = TCG_MAX_INSNS;
> -    }
> +    QEMU_BUILD_BUG_ON(CF_COUNT_MASK + 1 != TCG_MAX_INSNS);
> +

Previously we would allow max_insns = TCG_MAX_INSNS (512).
Now we only allow it to be 511...

-- PMM