[intermediate representation] fixed some bugs

lib/ir/basic_block.cpp

@@ -9,18 +9,22 @@ class phi_node;
 
 basic_block::basic_block(context &ctx, const std::string &name, function *parent):
   value(type::get_label_ty(ctx), name), ctx_(ctx), parent_(parent){
-
 }
 
 basic_block* basic_block::create(context &ctx, const std::string &name, function *parent){
   return new basic_block(ctx, name, parent);
 }
 
+void basic_block::add_predecessor(basic_block *pred) {
+  preds_.push_back(pred);
+}
+
 basic_block::iterator basic_block::get_first_non_phi(){
   auto it = begin();
   for(; it != end(); it++)
-  if(!dynamic_cast<phi_node*>(*it))
+  if(!dynamic_cast<phi_node*>(*it)){
     return it;
+  }
   return it;
 }