Re: [Qemu-devel] [PATCH v2 1/4] tcg/optimize: fix known-zero bits for right shift ops

[Michael Roth <mdroth@linux.vnet.ibm.com>]

Quoting Aurelien Jarno (2013-09-09 12:27:47)
> 32-bit versions of sar and shr ops should not propagate known-zero bits
> from the unused 32 high bits. For sar it could even lead to wrong code
> being generated.
> 
> Cc: Richard Henderson <rth@twiddle.net>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: qemu-stable@nongnu.org
> Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
> ---
>  tcg/optimize.c |   21 +++++++++++++++++----
>  1 file changed, 17 insertions(+), 4 deletions(-)

Ping, looking to pull this in for 1.7.1

> 
> diff --git a/tcg/optimize.c b/tcg/optimize.c
> index b29bf25..c539e39 100644
> --- a/tcg/optimize.c
> +++ b/tcg/optimize.c
> @@ -730,16 +730,29 @@ static TCGArg *tcg_constant_folding(TCGContext *s, uint16_t *tcg_opc_ptr,
>              mask = temps[args[1]].mask & mask;
>              break;
> 
> -        CASE_OP_32_64(sar):
> +        case INDEX_op_sar_i32:
> +            if (temps[args[2]].state == TCG_TEMP_CONST) {
> +                mask = ((int32_t)temps[args[1]].mask
> +                        >> temps[args[2]].val);
> +            }
> +            break;
> +        case INDEX_op_sar_i64:
>              if (temps[args[2]].state == TCG_TEMP_CONST) {
> -                mask = ((tcg_target_long)temps[args[1]].mask
> +                mask = ((int64_t)temps[args[1]].mask
>                          >> temps[args[2]].val);
>              }
>              break;
> 
> -        CASE_OP_32_64(shr):
> +        case INDEX_op_shr_i32:
>              if (temps[args[2]].state == TCG_TEMP_CONST) {
> -                mask = temps[args[1]].mask >> temps[args[2]].val;
> +                mask = ((uint32_t)temps[args[1]].mask
> +                        >> temps[args[2]].val);
> +            }
> +            break;
> +        case INDEX_op_shr_i64:
> +            if (temps[args[2]].state == TCG_TEMP_CONST) {
> +                mask = ((uint64_t)temps[args[1]].mask
> +                        >> temps[args[2]].val);
>              }
>              break;
> 
> -- 
> 1.7.10.4