Re: [RFC PATCH 3/4] tcg/ppc: Optimize memory ordering generation with lwsync

[Richard Henderson]

On 5/3/22 03:33, Nicholas Piggin wrote:
> lwsync orders more than just LD_LD, importantly it matches x86 and
> s390 default memory ordering.
>
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> ---
>   target/ppc/cpu.h         | 2 ++
>   tcg/ppc/tcg-target.c.inc | 2 +-
>   2 files changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/target/ppc/cpu.h b/target/ppc/cpu.h
> index c2b6c987c0..0b0e9761cd 100644
> --- a/target/ppc/cpu.h
> +++ b/target/ppc/cpu.h
> @@ -28,6 +28,8 @@
>   
>   #define TCG_GUEST_DEFAULT_MO 0
>   
> +#define PPC_LWSYNC_MO (TCG_MO_LD_LD | TCG_MO_LD_ST | TCG_MO_ST_ST)

You can't put this here...


> +
>   #define TARGET_PAGE_BITS_64K 16
>   #define TARGET_PAGE_BITS_16M 24
>   
> diff --git a/tcg/ppc/tcg-target.c.inc b/tcg/ppc/tcg-target.c.inc
> index 3ff845d063..b87fc2383e 100644
> --- a/tcg/ppc/tcg-target.c.inc
> +++ b/tcg/ppc/tcg-target.c.inc
> @@ -1834,7 +1834,7 @@ static void tcg_out_mb(TCGContext *s, TCGArg a0)
>   {
>       uint32_t insn = HWSYNC;
>       a0 &= TCG_MO_ALL;
> -    if (a0 == TCG_MO_LD_LD) {
> +    if ((a0 & PPC_LWSYNC_MO) == a0) {

... and have it used here.  You should have seen compilation failures for the missing 
symbol.  I can only assume you used a restricted --target-list in testing.

Anyway, it looks like a simpler test would be

    insn = (a0 & TCG_MO_ST_LD ? HWSYNC : LWSYNC);


r~