[Mesa-dev] [PATCH 04/23] i965/fs: fix requirements to allow type change in copy-propagation

[Jordan Justen]

Should the subject say something about not allowing a type size
change?

-Jordan

On 2016-05-03 05:21:53, Samuel Iglesias Gonsálvez wrote:
> From: Iago Toral Quiroga <itoral at igalia.com>
> 
> When source modifiers are present and the types of the source and
> the entry's source are different, there are certain cases in which
> we allow copy-propagation to change the type of source by the type
> of the entry's source we are copy propagating from.
> 
> However, it is not generally safe to do this if the types involved
> have different sizes, since parameters like the stride would change
> the semantics of the resulting instruction.
> 
> Prevents that we turn this:
> 
> load_payload(8) vgrf17:DF, |vgrf4+0.0|:DF 1sthalf
> mov(8) vgrf18:DF, vgrf17:DF 1sthalf
> load_payload(8) vgrf5:DF, vgrf18:DF, vgrf20:DF NoMask 1sthalf WE_all
> load_payload(8) vgrf21:UD, vgrf5+0.4<2>:UD 1sthalf
> mov(8) vgrf22:UD, vgrf21:UD 1sthalf
> 
> into:
> 
> load_payload(8) vgrf17:DF, |vgrf4+0.0|:DF 1sthalf
> mov(8) vgrf18:DF, |vgrf4+0.0|:DF 1sthalf
> load_payload(8) vgrf5:DF, |vgrf4+0.0|:DF, |vgrf4+2.0|:DF NoMask 1sthalf WE_all
> load_payload(8) vgrf21:UD, vgrf5+0.4<2>:UD 1sthalf
> mov(8) vgrf22:DF, |vgrf4+0.4|<2>:DF 1sthalf
> 
> where the semantics of the last instruccion have changed.
> ---
>  src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp b/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp
> index abc68c8..aa4c9c9 100644
> --- a/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp
> +++ b/src/mesa/drivers/dri/i965/brw_fs_copy_propagation.cpp
> @@ -411,8 +411,9 @@ fs_visitor::try_copy_propagate(fs_inst *inst, int arg, acp_entry *entry)
>        return false;
>  
>     if (has_source_modifiers &&
> -       entry->dst.type != inst->src[arg].type &&
> -       !inst->can_change_types())
> +       ((entry->dst.type != inst->src[arg].type &&
> +         !inst->can_change_types()) ||
> +        (type_sz(entry->dst.type) != type_sz(inst->src[arg].type))))
>        return false;
>  
>     if (devinfo->gen >= 8 && (entry->src.negate || entry->src.abs) &&
> -- 
> 2.5.0
> 
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