[Mesa-dev] [RFC PATCH 03/13] nir: fix output offset compute for dvec3/4

[Alejandro Piñeiro]

The offset compute was working fine for the case of attrib_slots=1,
and updating the offset for the following varying.

But in the case of attrib_slots=2 (so dvec3/4), we are basically
splitting the comp_slots needed in two outputs. In that case we can't
add to the offset the full size of the type.

v2: added assert and some parenthesis to improve readability (Jason)

Reviewed-by: Jason Ekstrand <jason at jlekstrand.net>
---
 src/compiler/nir/nir_gather_xfb_info.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/compiler/nir/nir_gather_xfb_info.c b/src/compiler/nir/nir_gather_xfb_info.c
index f8d4cd833c7..f4f597da4f5 100644
--- a/src/compiler/nir/nir_gather_xfb_info.c
+++ b/src/compiler/nir/nir_gather_xfb_info.c
@@ -81,7 +81,12 @@ add_var_xfb_outputs(nir_xfb_info *xfb,
          output->component_mask = (comp_mask >> (s * 4)) & 0xf;
 
          (*location)++;
-         *offset += comp_slots * 4;
+         /* attrib_slots would be only > 1 for doubles. On that case
+          * comp_slots will be a multiple of 2, so the following doesn't need
+          * to use DIV_ROUND_UP or similar
+          */
+         assert(comp_slots % attrib_slots == 0);
+         *offset += (comp_slots / attrib_slots) * 4;
       }
    }
 }
-- 
2.19.1