nir/lower_shader_calls: skip zero-sized qsort

Fixes UBSan:
src/compiler/nir/nir_lower_shader_calls.c:1681:7: runtime error: null pointer passed as argument 1, which is declared to never be null

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Timur Kristóf <timur.kristof@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/25853>

diff --git a/src/compiler/nir/nir_lower_shader_calls.c b/src/compiler/nir/nir_lower_shader_calls.c
index c10f930..d9e2a33 100644 (file)
--- a/src/compiler/nir/nir_lower_shader_calls.c
+++ b/src/compiler/nir/nir_lower_shader_calls.c
@@ -1678,10 +1678,12 @@ nir_opt_sort_and_pack_stack(nir_shader *shader,
       }
 
       /* Sort scratch item by component size. */
-      qsort(util_dynarray_begin(&ops),
-            util_dynarray_num_elements(&ops, struct scratch_item),
-            sizeof(struct scratch_item),
-            sort_scratch_item_by_size_and_value_id);
+      if (util_dynarray_num_elements(&ops, struct scratch_item)) {
+         qsort(util_dynarray_begin(&ops),
+               util_dynarray_num_elements(&ops, struct scratch_item),
+               sizeof(struct scratch_item),
+               sort_scratch_item_by_size_and_value_id);
+      }
 
       /* Reorder things on the stack */
       _mesa_hash_table_u64_clear(value_id_to_item);