mesa/spirv: Lower variable initializers for global variables

We lower variable initializers for local variables higher up in the
function but we never called nir_lower_variable_initializers for
anything else.

Cc: mesa-stable@lists.freedesktop.org
Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7296>
(cherry picked from commit 6b85a887ff)

.pick_status.json

@@ -4873,7 +4873,7 @@
         "description": "mesa/spirv: Lower variable initializers for global variables",
         "nominated": true,
         "nomination_type": 0,
-        "resolution": 0,
+        "resolution": 1,
         "master_sha": null,
         "because_sha": null
     },

src/mesa/main/glspirv.c

@@ -295,6 +295,13 @@ _mesa_spirv_to_nir(struct gl_context *ctx,
    }
    assert(exec_list_length(&nir->functions) == 1);
 
+   /* Now that we've deleted all but the main function, we can go ahead and
+    * lower the rest of the constant initializers.  We do this here so that
+    * nir_remove_dead_variables and split_per_member_structs below see the
+    * corresponding stores.
+    */
+   NIR_PASS_V(nir, nir_lower_variable_initializers, ~0);
+
    /* Split member structs.  We do this before lower_io_to_temporaries so that
     * it doesn't lower system values to temporaries by accident.
     */