[Mesa-dev] [PATCH v2 02/13] i965: Fix partial variable access for geometry shaders in SSO mode.

[Kenneth Graunke]

Without varying packing, if a VS writes a compound variable, and the GS
only reads part of it, the base location of the variable may not
actually be in the VUE map.

To cope with this, we do lowering in terms of varying slots, add any
constant offsets to the base, and then do the VUE map remapping.  This
ensures we only look up VUE map entries for slots which actually exist.

Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
---
 src/mesa/drivers/dri/i965/brw_nir.c | 38 +++++++++++++++++++++++++++++++++----
 1 file changed, 34 insertions(+), 4 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_nir.c b/src/mesa/drivers/dri/i965/brw_nir.c
index afb1f6d..f9e5c59 100644
--- a/src/mesa/drivers/dri/i965/brw_nir.c
+++ b/src/mesa/drivers/dri/i965/brw_nir.c
@@ -112,6 +112,27 @@ remap_vs_attrs(nir_block *block, void *closure)
    return true;
 }
 
+static bool
+remap_inputs_with_vue_map(nir_block *block, void *closure)
+{
+   const struct brw_vue_map *vue_map = closure;
+
+   nir_foreach_instr(block, instr) {
+      if (instr->type != nir_instr_type_intrinsic)
+         continue;
+
+      nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
+
+      if (intrin->intrinsic == nir_intrinsic_load_input ||
+          intrin->intrinsic == nir_intrinsic_load_per_vertex_input) {
+         int vue_slot = vue_map->varying_to_slot[intrin->const_index[0]];
+         assert(vue_slot != -1);
+         intrin->const_index[0] = vue_slot;
+      }
+   }
+   return true;
+}
+
 static void
 brw_nir_lower_inputs(nir_shader *nir,
                      const struct brw_device_info *devinfo,
@@ -180,15 +201,24 @@ brw_nir_lower_inputs(nir_shader *nir,
          brw_compute_vue_map(devinfo, &input_vue_map, inputs_read,
                              nir->info.separate_shader);
 
-         /* Start with the slot for the variable's base. */
          foreach_list_typed(nir_variable, var, node, &nir->inputs) {
-            assert(input_vue_map.varying_to_slot[var->data.location] != -1);
-            var->data.driver_location =
-               input_vue_map.varying_to_slot[var->data.location];
+            var->data.driver_location = var->data.location;
          }
 
          /* Inputs are stored in vec4 slots, so use type_size_vec4(). */
          nir_lower_io(nir, nir_var_shader_in, type_size_vec4);
+
+         /* This pass needs actual constants */
+         nir_opt_constant_folding(nir);
+
+         nir_foreach_overload(nir, overload) {
+            if (overload->impl) {
+               nir_builder_init(&params.b, overload->impl);
+               nir_foreach_block(overload->impl, add_const_offset_to_base, &params);
+               nir_foreach_block(overload->impl, remap_inputs_with_vue_map,
+                                 &input_vue_map);
+            }
+         }
       }
       break;
    }
-- 
2.6.3