spirv: Eliminate dead input/output variables after translation.

spirv_to_nir can generate input/output variables which are illegal
for the current shader stage, which would cause nir_validate_shader
to balk.  After my recent commit to start decorating arrays as compact,
dEQP-VK.spirv_assembly.instruction.graphics.module.same_module started
hitting validation errors due to outputs in a TCS (not intended for the
TCS at all) not being per-vertex arrays.

Thanks to Jason Ekstrand for suggesting this approach.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=109573
Fixes: ef99f4c8d17 compiler: Mark clip/cull distance arrays as compact before lowering.
Reviewed-by: Juan A. Suarez <[email protected]>

1 files changed, 20 insertions, 5 deletions

diff --git a/src/compiler/spirv/spirv_to_nir.c b/src/compiler/spirv/spirv_to_nir.c
index 5e8eb222555..8c07542f832 100644
--- a/src/compiler/spirv/spirv_to_nir.c
+++ b/src/compiler/spirv/spirv_to_nir.c
@@ -4497,20 +4497,35 @@ spirv_to_nir(const uint32_t *words, size_t word_count,
       }
    } while (progress);
 
+   vtn_assert(b->entry_point->value_type == vtn_value_type_function);
+   nir_function *entry_point = b->entry_point->func->impl->function;
+   vtn_assert(entry_point);
+
+   entry_point->is_entrypoint = true;
+
+   /* When multiple shader stages exist in the same SPIR-V module, we
+    * generate input and output variables for every stage, in the same
+    * NIR program.  These dead variables can be invalid NIR.  For example,
+    * TCS outputs must be per-vertex arrays (or decorated 'patch'), while
+    * VS output variables wouldn't be.
+    *
+    * To ensure we have valid NIR, we eliminate any dead inputs and outputs
+    * right away.  In order to do so, we must lower any constant initializers
+    * on outputs so nir_remove_dead_variables sees that they're written to.
+    */
+   nir_lower_constant_initializers(b->shader, nir_var_shader_out);
+   nir_remove_dead_variables(b->shader,
+                             nir_var_shader_in | nir_var_shader_out);
+
    /* We sometimes generate bogus derefs that, while never used, give the
     * validator a bit of heartburn.  Run dead code to get rid of them.
     */
    nir_opt_dce(b->shader);
 
-   vtn_assert(b->entry_point->value_type == vtn_value_type_function);
-   nir_function *entry_point = b->entry_point->func->impl->function;
-   vtn_assert(entry_point);
-
    /* Unparent the shader from the vtn_builder before we delete the builder */
    ralloc_steal(NULL, b->shader);
 
    ralloc_free(b);
 
-   entry_point->is_entrypoint = true;
    return entry_point;
 }