nir: Add helpers for lazy var creation.

This should make writing some lowering/meta code easier.  It also keeps
the num_inputs/outputs updated, when sometimes passes forgot to do so (for
example, nir_lower_input_attachments updated for one of the two vars it
creates).  The names of the variables change in many cases, but it's
probably nicer to see "VERT_ATTRIB_POS" than "in_0" or whatever.

I've only converted mesa core (compiler and GL), not all the driver meta
code.

Reviewed-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Reviewed-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/22809>

2 files changed, 5 insertions, 21 deletions

diff --git a/src/gallium/auxiliary/nir/nir_draw_helpers.c b/src/gallium/auxiliary/nir/nir_draw_helpers.c
index ad0d6d15ea1..2b362433f77 100644
--- a/src/gallium/auxiliary/nir/nir_draw_helpers.c
+++ b/src/gallium/auxiliary/nir/nir_draw_helpers.c
@@ -50,16 +50,9 @@ typedef struct {
 static nir_ssa_def *
 load_frag_coord(nir_builder *b)
 {
-   nir_foreach_shader_in_variable(var, b->shader) {
-      if (var->data.location == VARYING_SLOT_POS)
-         return nir_load_var(b, var);
-   }
-
-   nir_variable *pos = nir_variable_create(b->shader, nir_var_shader_in,
-                                           glsl_vec4_type(), NULL);
-   pos->data.location = VARYING_SLOT_POS;
+   nir_variable *pos = nir_get_variable_with_location(b->shader, nir_var_shader_in,
+                                                      VARYING_SLOT_POS, glsl_vec4_type());
    pos->data.interpolation = INTERP_MODE_NOPERSPECTIVE;
-   pos->data.driver_location = b->shader->num_inputs++;
    return nir_load_var(b, pos);
 }
 
diff --git a/src/gallium/auxiliary/nir/nir_to_tgsi.c b/src/gallium/auxiliary/nir/nir_to_tgsi.c
index 5d60915392f..cb95afa5383 100644
--- a/src/gallium/auxiliary/nir/nir_to_tgsi.c
+++ b/src/gallium/auxiliary/nir/nir_to_tgsi.c
@@ -3673,15 +3673,8 @@ nir_lower_primid_sysval_to_input_filter(const nir_instr *instr, const void *_dat
 static nir_ssa_def *
 nir_lower_primid_sysval_to_input_lower(nir_builder *b, nir_instr *instr, void *data)
 {
-   nir_variable *var = *(nir_variable **)data;
-   if (!var) {
-      var = nir_variable_create(b->shader, nir_var_shader_in, glsl_uint_type(), "gl_PrimitiveID");
-      var->data.location = VARYING_SLOT_PRIMITIVE_ID;
-      b->shader->info.inputs_read |= VARYING_BIT_PRIMITIVE_ID;
-      var->data.driver_location = b->shader->num_inputs++;
-
-      *(nir_variable **)data = var;
-   }
+   nir_variable *var = nir_get_variable_with_location(b->shader, nir_var_shader_in,
+                                                      VARYING_SLOT_PRIMITIVE_ID, glsl_uint_type());
 
    nir_io_semantics semantics = {
       .location = var->data.location,
@@ -3695,11 +3688,9 @@ nir_lower_primid_sysval_to_input_lower(nir_builder *b, nir_instr *instr, void *d
 static bool
 nir_lower_primid_sysval_to_input(nir_shader *s)
 {
-   nir_variable *input = NULL;
-
    return nir_shader_lower_instructions(s,
                                         nir_lower_primid_sysval_to_input_filter,
-                                        nir_lower_primid_sysval_to_input_lower, &input);
+                                        nir_lower_primid_sysval_to_input_lower, NULL);
 }
 
 const void *