nir,vtn: Add return info to parameters

Reviewed-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/33246>

src/compiler/nir/nir.h

@@ -3580,7 +3580,7 @@ typedef struct {
    uint8_t num_components;
    uint8_t bit_size;
 
-   /* True if this paramater is actually the function return variable */
+   /* True if this parameter is a deref used for returning values */
    bool is_return;
 
    bool implicit_conversion_prohibited;

src/compiler/spirv/vtn_cfg.c

@@ -331,6 +331,8 @@ vtn_cfg_handle_prepass_instruction(struct vtn_builder *b, SpvOp opcode,
          func->params[idx++] = (nir_parameter) {
             .num_components = nir_address_format_num_components(addr_format),
             .bit_size = nir_address_format_bit_size(addr_format),
+            .is_return = true,
+            .type = func_type->return_type->type,
          };
       }