spirv: Only emit functions which are actually used

Instead of emitting absolutely everything, just emit the few functions
that are actually referenced in some way by the entrypoint.  This should
save us quite a bit of time when handed large shader modules containing
many entrypoints.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Kristian H. Kristensen <hoegsberg@google.com>

src/compiler/spirv/spirv_to_nir.c

@@ -1394,8 +1394,11 @@ vtn_handle_function_call(struct vtn_builder *b, SpvOp opcode,
                          const uint32_t *w, unsigned count)
 {
    struct vtn_type *res_type = vtn_value(b, w[1], vtn_value_type_type)->type;
-   struct nir_function *callee =
+   struct vtn_function *vtn_callee =
-      vtn_value(b, w[3], vtn_value_type_function)->func->impl->function;
+      vtn_value(b, w[3], vtn_value_type_function)->func;
+   struct nir_function *callee = vtn_callee->impl->function;
+
+   vtn_callee->referenced = true;
 
    nir_call_instr *call = nir_call_instr_create(b->nb.shader, callee);
    for (unsigned i = 0; i < call->num_params; i++) {
@@ -3366,12 +3369,22 @@ spirv_to_nir(const uint32_t *words, size_t word_count,
 
    vtn_build_cfg(b, words, word_end);
 
-   foreach_list_typed(struct vtn_function, func, node, &b->functions) {
+   assert(b->entry_point->value_type == vtn_value_type_function);
-      b->const_table = _mesa_hash_table_create(b, _mesa_hash_pointer,
+   b->entry_point->func->referenced = true;
-                                               _mesa_key_pointer_equal);
 
-      vtn_function_emit(b, func, vtn_handle_body_instruction);
+   bool progress;
-   }
+   do {
+      progress = false;
+      foreach_list_typed(struct vtn_function, func, node, &b->functions) {
+         if (func->referenced && !func->emitted) {
+            b->const_table = _mesa_hash_table_create(b, _mesa_hash_pointer,
+                                                     _mesa_key_pointer_equal);
+
+            vtn_function_emit(b, func, vtn_handle_body_instruction);
+            progress = true;
+         }
+      }
+   } while (progress);
 
    assert(b->entry_point->value_type == vtn_value_type_function);
    nir_function *entry_point = b->entry_point->func->impl->function;

src/compiler/spirv/vtn_cfg.c

@@ -783,4 +783,6 @@ vtn_function_emit(struct vtn_builder *b, struct vtn_function *func,
     */
    if (b->has_loop_continue)
       nir_repair_ssa_impl(func->impl);
+
+   func->emitted = true;
 }

src/compiler/spirv/vtn_private.h

@@ -159,6 +159,9 @@ struct vtn_block {
 struct vtn_function {
    struct exec_node node;
 
+   bool referenced;
+   bool emitted;
+
    nir_function_impl *impl;
    struct vtn_block *start_block;