nir: Add helpers for getting input/output intrinsic sources.

With the many variants of IO intrinsics, particular sources are often in
different locations.  It's convenient to say "give me the indirect
offset" or "give me the vertex index" and have it just work, without
having to think about exactly which kind of intrinsic you have.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Jason Ekstrand <jason.ekstrand@intel.com>

src/glsl/nir/nir.h

@@ -1933,6 +1933,9 @@ void nir_assign_var_locations(struct exec_list *var_list,
 void nir_lower_io(nir_shader *shader,
                   nir_variable_mode mode,
                   int (*type_size)(const struct glsl_type *));
+nir_src *nir_get_io_indirect_src(nir_intrinsic_instr *instr);
+nir_src *nir_get_io_vertex_index_src(nir_intrinsic_instr *instr);
+
 void nir_lower_vars_to_ssa(nir_shader *shader);
 
 bool nir_remove_dead_variables(nir_shader *shader);

src/glsl/nir/nir_lower_io.c

@@ -328,3 +328,45 @@ nir_lower_io(nir_shader *shader, nir_variable_mode mode,
          nir_lower_io_impl(overload->impl, mode, type_size);
    }
 }
+
+/**
+ * Return the indirect source for a load/store indirect intrinsic.
+ */
+nir_src *
+nir_get_io_indirect_src(nir_intrinsic_instr *instr)
+{
+   switch (instr->intrinsic) {
+   case nir_intrinsic_load_input_indirect:
+   case nir_intrinsic_load_output_indirect:
+   case nir_intrinsic_load_uniform_indirect:
+      return &instr->src[0];
+   case nir_intrinsic_load_per_vertex_input_indirect:
+   case nir_intrinsic_load_per_vertex_output_indirect:
+   case nir_intrinsic_store_output_indirect:
+      return &instr->src[1];
+   case nir_intrinsic_store_per_vertex_output_indirect:
+      return &instr->src[2];
+   default:
+      return NULL;
+   }
+}
+
+/**
+ * Return the vertex index source for a load/store per_vertex intrinsic.
+ */
+nir_src *
+nir_get_io_vertex_index_src(nir_intrinsic_instr *instr)
+{
+   switch (instr->intrinsic) {
+   case nir_intrinsic_load_per_vertex_input:
+   case nir_intrinsic_load_per_vertex_output:
+   case nir_intrinsic_load_per_vertex_input_indirect:
+   case nir_intrinsic_load_per_vertex_output_indirect:
+      return &instr->src[0];
+   case nir_intrinsic_store_per_vertex_output:
+   case nir_intrinsic_store_per_vertex_output_indirect:
+      return &instr->src[1];
+   default:
+      return NULL;
+   }
+}