nir/lower_io: Make variable location assignment a manual operation

Previously, we just assigned variable locations in nir_lower_io.  Now, we
force the user to assign variable locations for us.  This gives the backend
a bit more control over where variables are placed.

v2: Rename from _packed to _scalar

Reviewed-by: Connor Abbott <cwabbott0@gmail.com>

src/glsl/nir/nir.h

@@ -1577,6 +1577,9 @@ void nir_lower_global_vars_to_local(nir_shader *shader);
 
 void nir_lower_locals_to_regs(nir_shader *shader);
 
+void nir_assign_var_locations_scalar(struct exec_list *var_list,
+                                     unsigned *size);
+
 void nir_lower_io(nir_shader *shader);
 
 void nir_lower_vars_to_ssa(nir_shader *shader);

src/glsl/nir/nir_lower_io.c

@@ -76,8 +76,8 @@ type_size(const struct glsl_type *type)
    return 0;
 }
 
-static void
+void
-assign_var_locations(struct exec_list *var_list, unsigned *size)
+nir_assign_var_locations_scalar(struct exec_list *var_list, unsigned *size)
 {
    unsigned location = 0;
 
@@ -96,14 +96,6 @@ assign_var_locations(struct exec_list *var_list, unsigned *size)
    *size = location;
 }
 
-static void
-assign_var_locations_shader(nir_shader *shader)
-{
-   assign_var_locations(&shader->inputs, &shader->num_inputs);
-   assign_var_locations(&shader->outputs, &shader->num_outputs);
-   assign_var_locations(&shader->uniforms, &shader->num_uniforms);
-}
-
 static bool
 deref_has_indirect(nir_deref_var *deref)
 {
@@ -304,8 +296,6 @@ nir_lower_io_impl(nir_function_impl *impl)
 void
 nir_lower_io(nir_shader *shader)
 {
-   assign_var_locations_shader(shader);
-
    nir_foreach_overload(shader, overload) {
       if (overload->impl)
          nir_lower_io_impl(overload->impl);

src/mesa/drivers/dri/i965/brw_fs_nir.cpp

@@ -105,6 +105,10 @@ fs_visitor::emit_nir_code()
    /* Get rid of split copies */
    nir_optimize(nir);
 
+   nir_assign_var_locations_scalar(&nir->uniforms, &nir->num_uniforms);
+   nir_assign_var_locations_scalar(&nir->inputs, &nir->num_inputs);
+   nir_assign_var_locations_scalar(&nir->outputs, &nir->num_outputs);
+
    nir_lower_io(nir);
    nir_validate_shader(nir);