ir3: add some preamble helpers

Helpers to check for preamble existence, find shpe, and create an empty
preamble.

Signed-off-by: Job Noorman <jnoorman@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/31222>

src/freedreno/ir3/ir3.c

@@ -586,6 +586,94 @@ ir3_block_get_last_phi(struct ir3_block *block)
    return last_phi;
 }
 
+struct ir3_instruction *
+ir3_find_shpe(struct ir3 *ir)
+{
+   if (!ir3_has_preamble(ir)) {
+      return NULL;
+   }
+
+   foreach_block (block, &ir->block_list) {
+      struct ir3_instruction *last = ir3_block_get_last_non_terminator(block);
+
+      if (last && last->opc == OPC_SHPE) {
+         return last;
+      }
+   }
+
+   unreachable("preamble without shpe");
+}
+
+struct ir3_instruction *
+ir3_create_empty_preamble(struct ir3 *ir)
+{
+   assert(!ir3_has_preamble(ir));
+
+   struct ir3_block *main_start_block = ir3_start_block(ir);
+
+   /* Create a preamble CFG similar to what the frontend would generate. Note
+    * that the empty else_block is important for ir3_after_preamble to work.
+    *
+    * shps_block:
+    * if (shps) {
+    *    getone_block:
+    *    if (getone) {
+    *       body_block:
+    *       shpe
+    *    }
+    * } else {
+    *    else_block:
+    * }
+    * main_start_block:
+    */
+   struct ir3_block *shps_block = ir3_block_create(ir);
+   struct ir3_block *getone_block = ir3_block_create(ir);
+   struct ir3_block *body_block = ir3_block_create(ir);
+   struct ir3_block *else_block = ir3_block_create(ir);
+   list_add(&else_block->node, &ir->block_list);
+   list_add(&body_block->node, &ir->block_list);
+   list_add(&getone_block->node, &ir->block_list);
+   list_add(&shps_block->node, &ir->block_list);
+
+   struct ir3_builder b = ir3_builder_at(ir3_after_block(shps_block));
+   ir3_SHPS(&b);
+   shps_block->successors[0] = getone_block;
+   ir3_block_add_predecessor(getone_block, shps_block);
+   ir3_block_link_physical(shps_block, getone_block);
+   shps_block->successors[1] = else_block;
+   ir3_block_add_predecessor(else_block, shps_block);
+   ir3_block_link_physical(shps_block, else_block);
+
+   b.cursor = ir3_after_block(getone_block);
+   ir3_GETONE(&b);
+   getone_block->divergent_condition = true;
+   getone_block->successors[0] = body_block;
+   ir3_block_add_predecessor(body_block, getone_block);
+   ir3_block_link_physical(getone_block, body_block);
+   getone_block->successors[1] = main_start_block;
+   ir3_block_add_predecessor(main_start_block, getone_block);
+   ir3_block_link_physical(getone_block, main_start_block);
+
+   b.cursor = ir3_after_block(body_block);
+   struct ir3_instruction *shpe = ir3_SHPE(&b);
+   shpe->barrier_class = shpe->barrier_conflict = IR3_BARRIER_CONST_W;
+   array_insert(body_block, body_block->keeps, shpe);
+   ir3_JUMP(&b);
+   body_block->successors[0] = main_start_block;
+   ir3_block_add_predecessor(main_start_block, body_block);
+   ir3_block_link_physical(body_block, main_start_block);
+
+   b.cursor = ir3_after_block(else_block);
+   ir3_JUMP(&b);
+   else_block->successors[0] = main_start_block;
+   ir3_block_add_predecessor(main_start_block, else_block);
+   ir3_block_link_physical(else_block, main_start_block);
+
+   main_start_block->reconvergence_point = true;
+
+   return shpe;
+}
+
 void
 ir3_block_add_predecessor(struct ir3_block *block, struct ir3_block *pred)
 {

src/freedreno/ir3/ir3.h

@@ -811,6 +811,17 @@ ir3_after_preamble(struct ir3 *ir)
       return block;
 }
 
+static inline bool
+ir3_has_preamble(struct ir3 *ir)
+{
+   return ir3_start_block(ir) != ir3_after_preamble(ir);
+}
+
+struct ir3_instruction *ir3_find_shpe(struct ir3 *ir);
+
+/* Create an empty preamble and return shpe. */
+struct ir3_instruction *ir3_create_empty_preamble(struct ir3 *ir);
+
 void ir3_block_add_predecessor(struct ir3_block *block, struct ir3_block *pred);
 void ir3_block_link_physical(struct ir3_block *pred, struct ir3_block *succ);
 void ir3_block_remove_predecessor(struct ir3_block *block,