Reimplement has_call_callback using ir_hierarchical_vistor

This has the added advantage that it will stop traversing the tree as
soon as the first call is found.

The output of all test cases was verified to be the same using diff.

ir_basic_block.cpp

@@ -30,17 +30,25 @@
 #include <stdio.h>
 #include "ir.h"
 #include "ir_visitor.h"
-#include "ir_visit_tree.h"
 #include "ir_basic_block.h"
 #include "glsl_types.h"
 
-static void
-has_call_callback(ir_instruction *ir, void *data)
-{
-   bool *has_call = (bool *)data;
+class ir_has_call_visitor : public ir_hierarchical_visitor {
+public:
+   ir_has_call_visitor()
+   {
+      has_call = false;
+   }
 
-   *has_call = *has_call || ir->as_call();
-}
+   virtual ir_visitor_status visit_enter(ir_call *ir)
+   {
+      (void) ir;
+      has_call = true;
+      return visit_stop;
+   }
+
+   bool has_call;
+};
 
 /**
  * Calls a user function for every basic block in the instruction stream.
@@ -108,7 +116,7 @@ void call_for_basic_blocks(exec_list *instructions,
 	    call_for_basic_blocks(&ir_sig->body, callback, data);
 	 }
       } else if (ir->as_assignment()) {
-	 bool has_call = false;
+	 ir_has_call_visitor v;
 
 	 /* If there's a call in the expression tree being assigned,
 	  * then that ends the BB too.
@@ -123,9 +131,8 @@ void call_for_basic_blocks(exec_list *instructions,
 	  * expression flattener may be useful before using the basic
 	  * block finder to get more maximal basic blocks out.
 	  */
-	 ir_visit_tree(ir, has_call_callback, &has_call);
-
-	 if (has_call) {
+	 ir->accept(&v);
+	 if (v.has_call) {
 	    callback(leader, ir, data);
 	    leader = NULL;
 	 }