Adding a warning when the current network or AIG has no POs.

src/base/abci/abc.c

@@ -575,6 +575,8 @@ void Abc_FrameUpdateGia( Abc_Frame_t * pAbc, Gia_Man_t * pNew )
         Abc_Print( -1, "Abc_FrameUpdateGia(): Tranformation has failed.\n" );
         return;
     }
+    if ( Gia_ManPoNum(pNew) == 0 )
+        Abc_Print( 0, "The current GIA has no primary outputs. Some commands may not work correctly.\n" );
     if ( pNew == pAbc->pGia )
         return;
     // transfer names

src/base/main/mainFrame.c

@@ -494,6 +494,9 @@ void Abc_FrameReplaceCurrentNetwork( Abc_Frame_t * p, Abc_Ntk_t * pNtk )
     if ( pNtk == NULL )
         return;
 
+    if ( Abc_NtkPoNum(pNtk) == 0 )
+        Abc_Print( 0, "The current network has no primary outputs. Some commands may not work correctly.\n" );
+
     // transfer the parameters to the new network
     if ( p->pNtkCur && Abc_FrameIsFlagEnabled( "backup" ) )
     {