I'd much rather land the first 3 patches from this series if possible.

https://patchwork.freedesktop.org/series/53800/

I've confirmed it packs the shaders you were looking at as expected once you patch 2 is applied. The series makes this code much more flexible (for future improvements) and easier to follow.

On 9/12/18 5:28 am, Rob Clark wrote:
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 <robdcl...@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) {

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