[Mesa-dev] [PATCH 1/2] nir: Add a safety check that we don't remove dead I/O vars after lowering.

[Eric Anholt]

The pass only looks at var load/store intrinsics, not input load/store
intrinsics, so assert that we don't see the other type.
---

I tripped over this limitation when trying to use the NIR linking
helpers in vc4.

 src/compiler/nir/nir_remove_dead_variables.c | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/src/compiler/nir/nir_remove_dead_variables.c b/src/compiler/nir/nir_remove_dead_variables.c
index a1fe0de9c61f..7a676f2309c4 100644
--- a/src/compiler/nir/nir_remove_dead_variables.c
+++ b/src/compiler/nir/nir_remove_dead_variables.c
@@ -28,7 +28,8 @@
 #include "nir.h"
 
 static void
-add_var_use_intrinsic(nir_intrinsic_instr *instr, struct set *live)
+add_var_use_intrinsic(nir_intrinsic_instr *instr, struct set *live,
+                      nir_variable_mode modes)
 {
    unsigned num_vars = nir_intrinsic_infos[instr->intrinsic].num_variables;
 
@@ -47,6 +48,16 @@ add_var_use_intrinsic(nir_intrinsic_instr *instr, struct set *live)
       break;
    }
 
+      /* This pass can't be used on I/O variables after they've been
+       * lowered.
+       */
+   case nir_intrinsic_load_input:
+      assert(!(modes & nir_var_shader_in));
+      break;
+   case nir_intrinsic_store_output:
+      assert(!(modes & nir_var_shader_out));
+      break;
+
    default:
       for (unsigned i = 0; i < num_vars; i++) {
          _mesa_set_add(live, instr->variables[i]->var);
@@ -84,7 +95,7 @@ add_var_use_tex(nir_tex_instr *instr, struct set *live)
 }
 
 static void
-add_var_use_shader(nir_shader *shader, struct set *live)
+add_var_use_shader(nir_shader *shader, struct set *live, nir_variable_mode modes)
 {
    nir_foreach_function(function, shader) {
       if (function->impl) {
@@ -92,7 +103,8 @@ add_var_use_shader(nir_shader *shader, struct set *live)
             nir_foreach_instr(instr, block) {
                switch(instr->type) {
                case nir_instr_type_intrinsic:
-                  add_var_use_intrinsic(nir_instr_as_intrinsic(instr), live);
+                  add_var_use_intrinsic(nir_instr_as_intrinsic(instr), live,
+                                        modes);
                   break;
 
                case nir_instr_type_call:
@@ -162,7 +174,7 @@ nir_remove_dead_variables(nir_shader *shader, nir_variable_mode modes)
    struct set *live =
       _mesa_set_create(NULL, _mesa_hash_pointer, _mesa_key_pointer_equal);
 
-   add_var_use_shader(shader, live);
+   add_var_use_shader(shader, live, modes);
 
    if (modes & nir_var_uniform)
       progress = remove_dead_vars(&shader->uniforms, live) || progress;
-- 
2.14.2