anv: Insert holes for non-existant XFB varyings

Thanks to optimizations, it's possible for varyings to get deleted but
still leave the variable there for nir_gather_xfb_info to find.  If we
get into this case, insert a hole.

Fixes: 36ee2fd61c8 "anv: Implement the basic form of..."
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3520>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3520>
(cherry picked from commit 993f866d2e31c06462b49d760debf64d14e54a68)

1 files changed, 17 insertions, 5 deletions

diff --git a/src/intel/vulkan/genX_pipeline.c b/src/intel/vulkan/genX_pipeline.c
index 0964ef5c604..ea2e38834e8 100644
--- a/src/intel/vulkan/genX_pipeline.c
+++ b/src/intel/vulkan/genX_pipeline.c
@@ -1415,11 +1415,23 @@ emit_3dstate_streamout(struct anv_pipeline *pipeline,
          next_offset[buffer] = output->offset +
                                __builtin_popcount(component_mask) * 4;
 
-         so_decl[stream][decls[stream]++] = (struct GENX(SO_DECL)) {
-            .OutputBufferSlot = buffer,
-            .RegisterIndex = vue_map->varying_to_slot[varying],
-            .ComponentMask = component_mask,
-         };
+         const int slot = vue_map->varying_to_slot[varying];
+         if (slot < 0) {
+            /* This can happen if the shader never writes to the varying.
+             * Insert a hole instead of actual varying data.
+             */
+            so_decl[stream][decls[stream]++] = (struct GENX(SO_DECL)) {
+               .HoleFlag = true,
+               .OutputBufferSlot = buffer,
+               .ComponentMask = component_mask,
+            };
+         } else {
+            so_decl[stream][decls[stream]++] = (struct GENX(SO_DECL)) {
+               .OutputBufferSlot = buffer,
+               .RegisterIndex = slot,
+               .ComponentMask = component_mask,
+            };
+         }
       }
 
       int max_decls = 0;