[Mesa-dev] [PATCH v2] i965/vec4: check writemask when bailing out at register coalesce

[Jason Ekstrand]

Cc'ing stable

On Fri, Sep 11, 2015 at 8:13 AM, Alejandro Piñeiro <apinheiro at igalia.com> wrote:
> opt_register_coalesce stopped to check previous instructions to
> coalesce with if somebody else was writing on the same
> destination. This can be optimized to check if somebody else was
> writing to the same channels of the same destination using the
> writemask.
>
> Shader DB results (taking into account only vec4):
>
> total instructions in shared programs: 1781593 -> 1734957 (-2.62%)
> instructions in affected programs:     1238390 -> 1191754 (-3.77%)
> helped:                                12782
> HURT:                                  0
> GAINED:                                0
> LOST:                                  0
>
> v2: removed some parenthesis, fixed indentation, as suggested by
>     Matt Turner
>
> Reviewed-by: Matt Turner <mattst88 at gmail.com>
> ---
>
> Patch updated after Matt review.
>
>  src/mesa/drivers/dri/i965/brw_vec4.cpp | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/src/mesa/drivers/dri/i965/brw_vec4.cpp b/src/mesa/drivers/dri/i965/brw_vec4.cpp
> index 85dc372..587a782 100644
> --- a/src/mesa/drivers/dri/i965/brw_vec4.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_vec4.cpp
> @@ -1089,11 +1089,12 @@ vec4_visitor::opt_register_coalesce()
>          if (interfered)
>             break;
>
> -         /* If somebody else writes our destination here, we can't coalesce
> -          * before that.
> +         /* If somebody else writes the same channels of our destination here,
> +          * we can't coalesce before that.
>            */
> -         if (inst->dst.in_range(scan_inst->dst, scan_inst->regs_written))
> -           break;
> +         if (inst->dst.in_range(scan_inst->dst, scan_inst->regs_written) &&
> +             (inst->dst.writemask & scan_inst->dst.writemask) != 0)
> +            break;
>
>           /* Check for reads of the register we're trying to coalesce into.  We
>            * can't go rewriting instructions above that to put some other value
> --
> 2.1.4
>
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