[Mesa-dev] [PATCH] i965: Fix number of slots in SSO mode when there are no user varyings.

[Jordan Justen]

Reviewed-by: Jordan Justen <jordan.l.justen at intel.com>

On 2017-01-08 15:45:49, Kenneth Graunke wrote:
> We want vue_map->num_slots to be one more than the final slot.
> 
> When assigning fixed slots, built-in slots, and non-SSO user varyings,
> we do slot++.  This leaves "slot" as one past the most recently assigned
> slot.  But for SSO user varyings, we computed slot based on the varying
> location value...and left it at that slot value.
> 
> To work around this inconsistency, I made num_slots be "slot + 1" if
> separate and "slot" otherwise.  The problem is...if there are no user
> varyings in SSO mode...then we would have done slot++ when assigning
> built-ins, so it would be off by one.  This resulted in loops from 0
> to vue_map->num_slots hitting a bonus BRW_VARYING_SLOT_PAD at the end.
> 
> This used to break the SIMD8 VS/TES backends, but I fixed that in
> commit 480d6c1653713dcae617ac523b2ca5deee01c845.  It's probably safe
> at this point, but we should fix it anyway.
> 
> To fix this, do slot++ in all cases.  For SSO mode, we overwrite slot
> for every varying, so this increment only matters on the last varying.
> Because we process varyings in order, this will set slot to 1 more
> than the highest assigned slot.
> 
> Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
> ---
>  src/mesa/drivers/dri/i965/brw_vue_map.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/src/mesa/drivers/dri/i965/brw_vue_map.c b/src/mesa/drivers/dri/i965/brw_vue_map.c
> index 982a31f9034..0d8f6c700b6 100644
> --- a/src/mesa/drivers/dri/i965/brw_vue_map.c
> +++ b/src/mesa/drivers/dri/i965/brw_vue_map.c
> @@ -181,14 +181,12 @@ brw_compute_vue_map(const struct gen_device_info *devinfo,
>        const int varying = ffsll(generics) - 1;
>        if (separate) {
>           slot = first_generic_slot + varying - VARYING_SLOT_VAR0;
> -         assign_vue_slot(vue_map, varying, slot);
> -      } else {
> -         assign_vue_slot(vue_map, varying, slot++);
>        }
> +      assign_vue_slot(vue_map, varying, slot++);
>        generics &= ~BITFIELD64_BIT(varying);
>     }
>  
> -   vue_map->num_slots = separate ? slot + 1 : slot;
> +   vue_map->num_slots = slot;
>     vue_map->num_per_vertex_slots = 0;
>     vue_map->num_per_patch_slots = 0;
>  }
> -- 
> 2.11.0
> 
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