[Mesa-dev] [PATCH] nir: fix compacting varyings when XFB outputs are present

[Samuel Pitoiset]

We shouldn't try to compact any varyings known as always
active IO, especially XFB outputs. For example, if one
component of an xfb output is also used as input varying
in the next stage, it shouldn't be compacted.

Because we look at the input varyings from the consumer
stage, we don't know if one of them is an XFB output. One
solution is to mark all components as used when
always_active_io is true to avoid wrong remapping.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset at gmail.com>
---
 src/compiler/nir/nir_linking_helpers.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/src/compiler/nir/nir_linking_helpers.c b/src/compiler/nir/nir_linking_helpers.c
index 85712a7cb1..88014e9a1d 100644
--- a/src/compiler/nir/nir_linking_helpers.c
+++ b/src/compiler/nir/nir_linking_helpers.c
@@ -236,6 +236,15 @@ get_slot_component_masks_and_interp_types(struct exec_list *var_list,
                get_interp_type(var, default_to_smooth_interp);
             interp_loc[location + i] = get_interp_loc(var);
 
+            if (var->data.always_active_io) {
+               /* Mark all components as used to avoid repacting xfb varyings
+                * wrongly. For instance, if one component of an xfb output is
+                * also used as input varying in the next stage.
+                */
+               comps[location + i] |= 0xf;
+               continue;
+            }
+
             if (dual_slot) {
                if (i & 1) {
                   comps[location + i] |= ((1 << comps_slot2) - 1);
-- 
2.19.1