Re: [PATCH v2 06/14] tcg/{i386, s390x}: Add earlyclobber to the op_add2's first output

[Philippe Mathieu-Daudé]

On 19/7/23 11:44, Ilya Leoshkevich wrote:
> i386 and s390x implementations of op_add2 require an earlyclobber,
> which is currently missing. This breaks VCKSM in s390x guests. E.g., on
> x86_64 the following op:
>
>      add2_i32 tmp2,tmp3,tmp2,tmp3,tmp3,tmp2   dead: 0 2 3 4 5  pref=none,0xffff
>
> is translated to:
>
>      addl     %ebx, %r12d
>      adcl     %r12d, %ebx
>
> Introduce a new C_N1_O1_I4 constraint, and make sure that earlyclobber
> of aliased outputs is honored.
>
> Cc: qemu-stable@nongnu.org
> Fixes: 82790a870992 ("tcg: Add markup for output requires new register")
> Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
> ---
>   tcg/i386/tcg-target-con-set.h  | 2 +-
>   tcg/i386/tcg-target.c.inc      | 2 +-
>   tcg/s390x/tcg-target-con-set.h | 5 ++---
>   tcg/s390x/tcg-target.c.inc     | 4 ++--
>   tcg/tcg.c                      | 8 +++++++-
>   5 files changed, 13 insertions(+), 8 deletions(-)
>
> diff --git a/tcg/i386/tcg-target-con-set.h b/tcg/i386/tcg-target-con-set.h
> index 91ceb0e1da2..cb4b25263e9 100644
> --- a/tcg/i386/tcg-target-con-set.h
> +++ b/tcg/i386/tcg-target-con-set.h
> @@ -53,4 +53,4 @@ C_O2_I1(r, r, L)
>   C_O2_I2(a, d, a, r)
>   C_O2_I2(r, r, L, L)
>   C_O2_I3(a, d, 0, 1, r)
> -C_O2_I4(r, r, 0, 1, re, re)
> +C_N1_O1_I4(r, r, 0, 1, re, re)

While here, please update the comment in header. Although the
description is not arch-specific; include/tcg/tcg.h or tcg/tcg.c
could hold it.

The patch LGTM but I don't feel confident enough to add a R-b tag.
If it still miss a R-b tag in a pair of days I'll have a deeper
look at it.

Regards,

Phil.