simplify spawn block handling

gen_input/templates/interp/CORENAME.cpp.gtl

@@ -181,6 +181,15 @@ protected:
         auto sign_mask = 1ULL<<(W-1);
         return (from & mask) | ((from & sign_mask) ? ~mask : 0);
     }
+    
+    inline void process_spawn_blocks() {
+        for(auto it = std::begin(spawn_blocks); it!=std::end(spawn_blocks);)
+             if(*it){
+                 (*it)();
+                 ++it;
+             } else
+                 spawn_blocks.erase(it);
+    }
 <%functions.each{ it.eachLine { %>
     ${it}<%}%>
 <%}%>
@@ -226,7 +235,7 @@ private:
         <%instr.behavior.eachLine{%>${it}
         <%}%>} catch(...){}
         // post execution stuff
-        for(auto& spawn_block:spawn_blocks) spawn_block();
+        process_spawn_blocks();
         if(this->sync_exec && POST_SYNC) this->do_sync(POST_SYNC, ${idx});
         // trap check
         if(*trap_state!=0){