[Mesa-dev] [PATCH 3/3] nir: fixed some missed varying compaction opportunities

[Rob Clark]

Previously, if we had a .z or .w component that could be compacted
to .y, we'd could overlook that opportunity.

Signed-off-by: Rob Clark <robdclark at gmail.com>
---
 src/compiler/nir/nir_linking_helpers.c | 30 ++++++++++++++++++++------
 1 file changed, 23 insertions(+), 7 deletions(-)

diff --git a/src/compiler/nir/nir_linking_helpers.c b/src/compiler/nir/nir_linking_helpers.c
index 1ab9c095657..ce368a3c132 100644
--- a/src/compiler/nir/nir_linking_helpers.c
+++ b/src/compiler/nir/nir_linking_helpers.c
@@ -431,12 +431,30 @@ compact_components(nir_shader *producer, nir_shader *consumer, uint8_t *comps,
          uint8_t interp = get_interp_type(var, type, default_to_smooth_interp);
          for (; cursor[interp] < 32; cursor[interp]++) {
             uint8_t cursor_used_comps = comps[cursor[interp]];
+            uint8_t unused_comps = ~cursor_used_comps;
 
-            /* We couldn't find anywhere to pack the varying continue on. */
-            if (cursor[interp] == location &&
-                (var->data.location_frac == 0 ||
-                 cursor_used_comps & ((1 << (var->data.location_frac)) - 1)))
-               break;
+            /* Don't search beyond our current location, we are just trying
+             * to pack later varyings to lower positions:
+             */
+            if (cursor[interp] == location) {
+               if (var->data.location_frac == 0)
+                  break;
+
+               /* If not already aligned to slot, see if we can shift it up.
+                * Note that if we get this far it is a scalar so we know that
+                * shifting this var to any other open position won't conflict
+                * with it's current position.
+                */
+               unsigned p = ffs(unused_comps & 0xf);
+               if (!p)
+                  break;
+
+               /* ffs returns 1 for bit zero: */
+               p--;
+
+               if (p >= var->data.location_frac)
+                  break;
+            }
 
             /* We can only pack varyings with matching interpolation types */
             if (interp_type[cursor[interp]] != interp)
@@ -460,8 +478,6 @@ compact_components(nir_shader *producer, nir_shader *consumer, uint8_t *comps,
             if (!cursor_used_comps)
                continue;
 
-            uint8_t unused_comps = ~cursor_used_comps;
-
             for (unsigned i = 0; i < 4; i++) {
                uint8_t new_var_comps = 1 << i;
                if (unused_comps & new_var_comps) {
-- 
2.19.2