Adding cyclicity check for netlist with boxes.

6 files changed, 403 insertions, 3 deletions

diff --git a/src/base/abc/abc.h b/src/base/abc/abc.h
index 62df9450..eb21b091 100644
--- a/src/base/abc/abc.h
+++ b/src/base/abc/abc.h
@@ -610,6 +610,7 @@ extern ABC_DLL Vec_Ptr_t *        Abc_NtkDfsIter( Abc_Ntk_t * pNtk, int fCollect
 extern ABC_DLL Vec_Ptr_t *        Abc_NtkDfsIterNodes( Abc_Ntk_t * pNtk, Vec_Ptr_t * vRoots );
 extern ABC_DLL Vec_Ptr_t *        Abc_NtkDfsHie( Abc_Ntk_t * pNtk, int fCollectAll );
 extern ABC_DLL int                Abc_NtkIsDfsOrdered( Abc_Ntk_t * pNtk );
+extern ABC_DLL Vec_Ptr_t *        Abc_NtkDfsWithBoxes( Abc_Ntk_t * pNtk );
 extern ABC_DLL Vec_Ptr_t *        Abc_NtkSupport( Abc_Ntk_t * pNtk );
 extern ABC_DLL Vec_Ptr_t *        Abc_NtkNodeSupport( Abc_Ntk_t * pNtk, Abc_Obj_t ** ppNodes, int nNodes );
 extern ABC_DLL Vec_Ptr_t *        Abc_AigDfs( Abc_Ntk_t * pNtk, int fCollectAll, int fCollectCos );
@@ -619,6 +620,7 @@ extern ABC_DLL Vec_Vec_t *        Abc_NtkLevelize( Abc_Ntk_t * pNtk );
 extern ABC_DLL int                Abc_NtkLevel( Abc_Ntk_t * pNtk );
 extern ABC_DLL int                Abc_NtkLevelReverse( Abc_Ntk_t * pNtk );
 extern ABC_DLL int                Abc_NtkIsAcyclic( Abc_Ntk_t * pNtk );
+extern ABC_DLL int                Abc_NtkIsAcyclicWithBoxes( Abc_Ntk_t * pNtk );
 extern ABC_DLL Vec_Ptr_t *        Abc_AigGetLevelizedOrder( Abc_Ntk_t * pNtk, int fCollectCis );
 /*=== abcFanio.c ==========================================================*/
 extern ABC_DLL void               Abc_ObjAddFanin( Abc_Obj_t * pObj, Abc_Obj_t * pFanin );
diff --git a/src/base/abc/abcDfs.c b/src/base/abc/abcDfs.c
index 08b62389..e6c9226f 100644
--- a/src/base/abc/abcDfs.c
+++ b/src/base/abc/abcDfs.c
@@ -687,6 +687,95 @@ int Abc_NtkIsDfsOrdered( Abc_Ntk_t * pNtk )
     return 1;
 }
 
+/**Function*************************************************************
+
+  Synopsis    [Create DFS ordering of nets.]
+
+  Description []
+               
+  SideEffects []
+
+  SeeAlso     []
+
+***********************************************************************/
+void Abc_NtkDfsNets_rec( Abc_Obj_t * pNet, Vec_Ptr_t * vNets )
+{
+    Abc_Obj_t * pNext;
+    Abc_Obj_t * pNode; int i;
+    assert( Abc_ObjIsNet(pNet) );
+    if ( Abc_NodeIsTravIdCurrent( pNet ) )
+        return;
+    Abc_NodeSetTravIdCurrent( pNet );
+    pNode = Abc_ObjFanin0( pNet );
+    Abc_ObjForEachFanin( pNode, pNext, i )
+        Abc_NtkDfsNets_rec( pNext, vNets );
+    Abc_ObjForEachFanout( pNode, pNext, i )
+        Vec_PtrPush( vNets, pNext );
+}
+Vec_Ptr_t * Abc_NtkDfsNets( Abc_Ntk_t * pNtk )
+{
+    Vec_Ptr_t * vNets;
+    Abc_Obj_t * pObj; int i;
+    vNets = Vec_PtrAlloc( 100 );
+    Abc_NtkIncrementTravId( pNtk );
+    Abc_NtkForEachCi( pNtk, pObj, i )
+        Abc_NodeSetTravIdCurrent( Abc_ObjFanout0(pObj) );
+    Abc_NtkForEachCi( pNtk, pObj, i )
+        Vec_PtrPush( vNets, Abc_ObjFanout0(pObj) );
+    Abc_NtkForEachCo( pNtk, pObj, i )
+        Abc_NtkDfsNets_rec( Abc_ObjFanin0(pObj), vNets );
+    return vNets;
+}
+
+/**Function*************************************************************
+
+  Synopsis    [Returns the DFS ordered array of logic nodes.]
+
+  Description [Collects only the internal nodes, leaving out CIs and CO.
+  However it marks with the current TravId both CIs and COs.]
+               
+  SideEffects []
+
+  SeeAlso     []
+
+***********************************************************************/
+void Abc_NtkDfsWithBoxes_rec( Abc_Obj_t * pNode, Vec_Ptr_t * vNodes )
+{
+    Abc_Obj_t * pFanin;
+    int i;
+    assert( !Abc_ObjIsNet(pNode) );
+    if ( Abc_ObjIsBo(pNode) )
+        pNode = Abc_ObjFanin0(pNode);
+    if ( Abc_ObjIsPi(pNode) )
+        return;
+    assert( Abc_ObjIsNode( pNode ) || Abc_ObjIsBox( pNode ) );
+    if ( Abc_NodeIsTravIdCurrent( pNode ) )
+        return;
+    Abc_NodeSetTravIdCurrent( pNode );
+    Abc_ObjForEachFanin( pNode, pFanin, i )
+    {
+        if ( Abc_ObjIsBox(pNode) )
+            pFanin = Abc_ObjFanin0(pFanin);
+        assert( Abc_ObjIsNet(pFanin) );
+        Abc_NtkDfsWithBoxes_rec( Abc_ObjFanin0Ntk(pFanin), vNodes );
+    }
+    Vec_PtrPush( vNodes, pNode );
+}
+Vec_Ptr_t * Abc_NtkDfsWithBoxes( Abc_Ntk_t * pNtk )
+{
+    Vec_Ptr_t * vNodes;
+    Abc_Obj_t * pObj;
+    int i;
+    Abc_NtkIncrementTravId( pNtk );
+    vNodes = Vec_PtrAlloc( 100 );
+    Abc_NtkForEachPo( pNtk, pObj, i )
+    {
+        assert( Abc_ObjIsNet(Abc_ObjFanin0(pObj)) );
+        Abc_NtkDfsWithBoxes_rec( Abc_ObjFanin0Ntk(Abc_ObjFanin0(pObj)), vNodes );
+    }
+    return vNodes;
+}
+
 
 /**Function*************************************************************
 
@@ -1353,6 +1442,99 @@ int Abc_NtkIsAcyclic( Abc_Ntk_t * pNtk )
     }
     return fAcyclic;
 }
+ 
+/**Function*************************************************************
+
+  Synopsis    [Checks for the loops with boxes.]
+
+  Description []
+                
+  SideEffects []
+
+  SeeAlso     []
+
+***********************************************************************/
+int Abc_NtkIsAcyclicWithBoxes_rec( Abc_Obj_t * pNode )
+{
+    Abc_Ntk_t * pNtk = pNode->pNtk;
+    Abc_Obj_t * pFanin;
+    int fAcyclic, i;
+    assert( !Abc_ObjIsNet(pNode) );
+    if ( Abc_ObjIsBo(pNode) )
+        pNode = Abc_ObjFanin0(pNode);
+    if ( Abc_ObjIsPi(pNode) )
+        return 1;
+    assert( Abc_ObjIsNode(pNode) || Abc_ObjIsBox(pNode) );
+    // make sure the node is not visited
+    assert( !Abc_NodeIsTravIdPrevious(pNode) );
+    // check if the node is part of the combinational loop
+    if ( Abc_NodeIsTravIdCurrent(pNode) )
+    {
+        fprintf( stdout, "Network \"%s\" contains combinational loop!\n", Abc_NtkName(pNtk) );
+        if ( Abc_ObjIsBox(pNode) )
+            fprintf( stdout, "Box \"%s\" is encountered twice on the following path to the COs:\n", Abc_ObjName(pNode) );
+        else
+            fprintf( stdout, "Node \"%s\" is encountered twice on the following path to the COs:\n", Abc_ObjName(Abc_ObjFanout0(pNode)) );
+        return 0;
+    }
+    // mark this node as a node on the current path
+    Abc_NodeSetTravIdCurrent( pNode );
+    // visit the transitive fanin
+    Abc_ObjForEachFanin( pNode, pFanin, i )
+    { 
+        if ( Abc_ObjIsBox(pNode) )
+            pFanin = Abc_ObjFanin0(pFanin);
+        pFanin = Abc_ObjFanin0Ntk(pFanin);
+        // make sure there is no mixing of networks
+        assert( pFanin->pNtk == pNode->pNtk );
+        // check if the fanin is visited
+        if ( Abc_ObjIsPi(pFanin) )
+            continue;
+        if ( Abc_ObjIsBo(pFanin) )
+            pFanin = Abc_ObjFanin0(pFanin);
+        assert( Abc_ObjIsNode(pFanin) || Abc_ObjIsBox(pFanin) );
+        if ( Abc_NodeIsTravIdPrevious(pFanin) ) 
+            continue;
+        // traverse the fanin's cone searching for the loop
+        if ( (fAcyclic = Abc_NtkIsAcyclicWithBoxes_rec(pFanin)) )
+            continue;
+        // return as soon as the loop is detected
+        fprintf( stdout, " %s ->", Abc_ObjName( Abc_ObjIsBox(pFanin) ? pFanin : Abc_ObjFanout0(pFanin) ) );
+        return 0;
+    }
+    // mark this node as a visited node
+    assert( Abc_ObjIsNode(pNode) || Abc_ObjIsBox(pNode) );
+    Abc_NodeSetTravIdPrevious( pNode );
+    return 1;
+}
+int Abc_NtkIsAcyclicWithBoxes( Abc_Ntk_t * pNtk )
+{
+    Abc_Obj_t * pNode;
+    int fAcyclic;
+    int i;
+    // set the traversal ID for this DFS ordering
+    Abc_NtkIncrementTravId( pNtk );   
+    Abc_NtkIncrementTravId( pNtk );   
+    // pNode->TravId == pNet->nTravIds      means "pNode is on the path"
+    // pNode->TravId == pNet->nTravIds - 1  means "pNode is visited but is not on the path"
+    // pNode->TravId <  pNet->nTravIds - 1  means "pNode is not visited"
+    // traverse the network to detect cycles
+    fAcyclic = 1;
+    Abc_NtkForEachPo( pNtk, pNode, i )
+    {
+        pNode = Abc_ObjFanin0Ntk(Abc_ObjFanin0(pNode));
+        if ( Abc_NodeIsTravIdPrevious(pNode) )
+            continue;
+        // traverse the output logic cone
+        if ( (fAcyclic = Abc_NtkIsAcyclicWithBoxes_rec(pNode)) )
+            continue;
+        // stop as soon as the first loop is detected
+        fprintf( stdout, " PO \"%s\"\n", Abc_ObjName(Abc_ObjFanout0(pNode)) );
+        break;
+    }
+    return fAcyclic;
+}
+
 
 
 /**Function*************************************************************
diff --git a/src/base/abc/abcHieGia.c b/src/base/abc/abcHieGia.c
new file mode 100644
index 00000000..1586dcd7
--- /dev/null
+++ b/src/base/abc/abcHieGia.c
@@ -0,0 +1,184 @@
+/**CFile****************************************************************
+
+  FileName    [abcHieGia.c]
+
+  SystemName  [ABC: Logic synthesis and verification system.]
+
+  PackageName [Network and node package.]
+
+  Synopsis    [Procedures to handle hierarchy.]
+
+  Author      [Alan Mishchenko]
+  
+  Affiliation [UC Berkeley]
+
+  Date        [Ver. 1.0. Started - June 20, 2005.]
+
+  Revision    [$Id: abcHieGia.c,v 1.00 2005/06/20 00:00:00 alanmi Exp $]
+
+***********************************************************************/
+
+#include "abc.h"
+
+ABC_NAMESPACE_IMPL_START
+
+
+////////////////////////////////////////////////////////////////////////
+///                        DECLARATIONS                              ///
+////////////////////////////////////////////////////////////////////////
+
+////////////////////////////////////////////////////////////////////////
+///                     FUNCTION DEFINITIONS                         ///
+////////////////////////////////////////////////////////////////////////
+
+/**Function*************************************************************
+
+  Synopsis    [Transfers the AIG from one manager into another.]
+
+  Description []
+               
+  SideEffects []
+
+  SeeAlso     []
+
+***********************************************************************/
+void Abc_NodeStrashToGia_rec( Gia_Man_t * pNew, Hop_Obj_t * pObj )
+{
+    assert( !Hop_IsComplement(pObj) );
+    if ( !Hop_ObjIsNode(pObj) || Hop_ObjIsMarkA(pObj) )
+        return;
+    Abc_NodeStrashToGia_rec( pNew, Hop_ObjFanin0(pObj) ); 
+    Abc_NodeStrashToGia_rec( pNew, Hop_ObjFanin1(pObj) );
+    pObj->iData = Gia_ManHashAnd( pNew, Hop_ObjChild0CopyI(pObj), Hop_ObjChild1CopyI(pObj) );
+    assert( !Hop_ObjIsMarkA(pObj) ); // loop detection
+    Hop_ObjSetMarkA( pObj );
+}
+int Abc_NodeStrashToGia( Gia_Man_t * pNew, Abc_Obj_t * pNode )
+{
+    Hop_Man_t * pMan = (Hop_Man_t *)pNode->pNtk->pManFunc;
+    Hop_Obj_t * pRoot = (Hop_Obj_t *)pNode->pData;
+    Abc_Obj_t * pFanin;  int i;
+    assert( Abc_ObjIsNode(pNode) );
+    assert( Abc_NtkHasAig(pNode->pNtk) && !Abc_NtkIsStrash(pNode->pNtk) );
+    // check the constant case
+    if ( Abc_NodeIsConst(pNode) || Hop_Regular(pRoot) == Hop_ManConst1(pMan) )
+        return Abc_LitNotCond( 1, Hop_IsComplement(pRoot) );
+    // set elementary variables
+    Abc_ObjForEachFanin( pNode, pFanin, i )
+        assert( pFanin->iTemp != -1 );
+    Abc_ObjForEachFanin( pNode, pFanin, i )
+        Hop_IthVar(pMan, i)->iData = pFanin->iTemp;
+    // strash the AIG of this node
+    Abc_NodeStrashToGia_rec( pNew, Hop_Regular(pRoot) );
+    Hop_ConeUnmark_rec( Hop_Regular(pRoot) );
+    return Abc_LitNotCond( Hop_Regular(pRoot)->iData, Hop_IsComplement(pRoot) );
+}
+
+
+/**Function*************************************************************
+
+  Synopsis    [Flattens the logic hierarchy of the netlist.]
+
+  Description []
+               
+  SideEffects []
+
+  SeeAlso     []
+
+***********************************************************************/
+void Gia_ManFlattenLogicHierarchy_rec( Gia_Man_t * pNew, Abc_Ntk_t * pNtk, int * pCounter )
+{
+    Vec_Ptr_t * vDfs = (Vec_Ptr_t *)pNtk->pData;
+    Abc_Obj_t * pObj, * pTerm; 
+    int i, k; (*pCounter)++;
+    //printf( "[%d:%d] ", Abc_NtkPiNum(pNtk), Abc_NtkPoNum(pNtk) );
+    Vec_PtrForEachEntry( Abc_Obj_t *, vDfs, pObj, i )
+    {
+        if ( Abc_ObjIsNode(pObj) )
+            Abc_ObjFanout0(pObj)->iTemp = Abc_NodeStrashToGia( pNew, pObj );
+        else
+        {
+            Abc_Ntk_t * pModel = (Abc_Ntk_t *)pObj->pData;
+            assert( !Abc_ObjIsLatch(pObj) );
+            assert( Abc_NtkPiNum(pModel) == Abc_ObjFaninNum(pObj) );
+            assert( Abc_NtkPoNum(pModel) == Abc_ObjFanoutNum(pObj) );
+            Abc_NtkFillTemp( pModel );
+            Abc_ObjForEachFanin( pObj, pTerm, k )
+            {
+                assert( Abc_ObjIsNet(Abc_ObjFanin0(pTerm)) );
+//                Abc_ObjFanout0(Abc_NtkPi(pModel, k))->iTemp = Gia_ManAppendBuf( pNew, Abc_ObjFanin0(pTerm)->iTemp );
+                Abc_ObjFanout0(Abc_NtkPi(pModel, k))->iTemp = Abc_ObjFanin0(pTerm)->iTemp;
+            }
+            Gia_ManFlattenLogicHierarchy_rec( pNew, pModel, pCounter );
+            Abc_ObjForEachFanout( pObj, pTerm, k )
+            {
+                assert( Abc_ObjIsNet(Abc_ObjFanout0(pTerm)) );
+//                Abc_ObjFanout0(pTerm)->iTemp = Gia_ManAppendBuf( pNew, Abc_ObjFanin0(Abc_NtkPo(pModel, k))->iTemp );
+                Abc_ObjFanout0(pTerm)->iTemp = Abc_ObjFanin0(Abc_NtkPo(pModel, k))->iTemp;
+            }
+        }
+    }
+}
+Gia_Man_t * Gia_ManFlattenLogicHierarchy( Abc_Ntk_t * pNtk )
+{
+    Gia_Man_t * pNew, * pTemp; 
+    Abc_Ntk_t * pModel;
+    Abc_Obj_t * pTerm;
+    int i, Counter = -1;
+    assert( Abc_NtkIsNetlist(pNtk) );
+
+//    Abc_NtkPrintBoxInfo( pNtk );
+    Abc_NtkFillTemp( pNtk );
+
+    // start the manager
+    pNew = Gia_ManStart( Abc_NtkObjNumMax(pNtk) );
+    pNew->pName = Abc_UtilStrsav(pNtk->pName);
+    pNew->pSpec = Abc_UtilStrsav(pNtk->pSpec);
+
+    // create PIs and buffers
+    Abc_NtkForEachPi( pNtk, pTerm, i )
+        pTerm->iTemp = Gia_ManAppendCi( pNew );
+    Abc_NtkForEachPi( pNtk, pTerm, i )
+//        Abc_ObjFanout0(pTerm)->iTemp = Gia_ManAppendBuf( pNew, pTerm->iTemp );
+        Abc_ObjFanout0(pTerm)->iTemp = pTerm->iTemp;
+
+    // create DFS order of nets
+    if ( !pNtk->pDesign )
+        pNtk->pData = Abc_NtkDfsWithBoxes( pNtk );
+    else
+        Vec_PtrForEachEntry( Abc_Ntk_t *, pNtk->pDesign->vModules, pModel, i )
+            pModel->pData = Abc_NtkDfsWithBoxes( pModel );
+
+    // call recursively
+    Gia_ManHashAlloc( pNew );
+    Gia_ManFlattenLogicHierarchy_rec( pNew, pNtk, &Counter );
+    Gia_ManHashStop( pNew );
+    printf( "Hierarchy reader flattened %d instances of logic boxes.\n", Counter );
+
+    // delete DFS order of nets
+    if ( !pNtk->pDesign )
+        Vec_PtrFreeP( (Vec_Ptr_t **)&pNtk->pData );
+    else
+        Vec_PtrForEachEntry( Abc_Ntk_t *, pNtk->pDesign->vModules, pModel, i )
+            Vec_PtrFreeP( (Vec_Ptr_t **)&pModel->pData );
+
+    // create buffers and POs
+    Abc_NtkForEachPo( pNtk, pTerm, i )
+//        pTerm->iTemp = Gia_ManAppendBuf( pNew, Abc_ObjFanin0(pTerm)->iTemp );
+        pTerm->iTemp = Abc_ObjFanin0(pTerm)->iTemp;
+    Abc_NtkForEachPo( pNtk, pTerm, i )
+        Gia_ManAppendCo( pNew, pTerm->iTemp );
+
+    pNew = Gia_ManCleanup( pTemp = pNew );
+    Gia_ManStop( pTemp );
+    return pNew;
+}
+
+
+////////////////////////////////////////////////////////////////////////
+///                       END OF FILE                                ///
+////////////////////////////////////////////////////////////////////////
+
+
+ABC_NAMESPACE_IMPL_END
+
diff --git a/src/base/abc/module.make b/src/base/abc/module.make
index e7c6345d..34517b04 100644
--- a/src/base/abc/module.make
+++ b/src/base/abc/module.make
@@ -8,6 +8,7 @@ SRC +=    src/base/abc/abcAig.c \
     src/base/abc/abcFunc.c \
     src/base/abc/abcHie.c \
     src/base/abc/abcHieCec.c \
+    src/base/abc/abcHieGia.c \
     src/base/abc/abcHieNew.c \
     src/base/abc/abcLatch.c \
     src/base/abc/abcLib.c \
diff --git a/src/base/io/io.c b/src/base/io/io.c
index 39c08db4..42a4a370 100644
--- a/src/base/io/io.c
+++ b/src/base/io/io.c
@@ -170,13 +170,14 @@ int IoCommandRead( Abc_Frame_t * pAbc, int argc, char ** argv )
     char Command[1000];
     Abc_Ntk_t * pNtk;
     char * pFileName, * pTemp;
-    int c, fCheck, fBarBufs;
+    int c, fCheck, fBarBufs, fReadGia;
 
     fCheck = 1;
     fBarBufs = 0;
+    fReadGia = 0;
     glo_fMapped = 0;
     Extra_UtilGetoptReset();
-    while ( ( c = Extra_UtilGetopt( argc, argv, "mcbh" ) ) != EOF )
+    while ( ( c = Extra_UtilGetopt( argc, argv, "mcbgh" ) ) != EOF )
     {
         switch ( c )
         {
@@ -189,6 +190,9 @@ int IoCommandRead( Abc_Frame_t * pAbc, int argc, char ** argv )
             case 'b':
                 fBarBufs ^= 1;
                 break;
+            case 'g':
+                fReadGia ^= 1;
+                break;
             case 'h':
                 goto usage;
             default:
@@ -225,6 +229,20 @@ int IoCommandRead( Abc_Frame_t * pAbc, int argc, char ** argv )
         Cmd_CommandExecute( pAbc, Command );
         return 0;
     }
+    if ( fReadGia )
+    {
+        extern Gia_Man_t * Gia_ManFlattenLogicHierarchy( Abc_Ntk_t * pNtk );
+        Abc_Ntk_t * pNtk = Io_ReadNetlist( pFileName, Io_ReadFileType(pFileName), fCheck );
+        Gia_Man_t * pGia = Gia_ManFlattenLogicHierarchy( pNtk );
+        Abc_NtkDelete( pNtk );
+        if ( pGia == NULL )
+        {
+            Abc_Print( 1, "Abc_CommandBlast(): Bit-blasting has failed.\n" );
+            return 0;
+        }
+        Abc_FrameUpdateGia( pAbc, pGia );
+        return 0;
+    }
     // check if the library is available
     if ( glo_fMapped && Abc_FrameReadLibGen() == NULL )
     {
@@ -247,13 +265,14 @@ int IoCommandRead( Abc_Frame_t * pAbc, int argc, char ** argv )
     return 0;
 
 usage:
-    fprintf( pAbc->Err, "usage: read [-mcbh] <file>\n" );
+    fprintf( pAbc->Err, "usage: read [-mcbgh] <file>\n" );
     fprintf( pAbc->Err, "\t         replaces the current network by the network read from <file>\n" );
     fprintf( pAbc->Err, "\t         by calling the parser that matches the extension of <file>\n" );
     fprintf( pAbc->Err, "\t         (to read a hierarchical design, use \"read_hie\")\n" );
     fprintf( pAbc->Err, "\t-m     : toggle reading mapped Verilog [default = %s]\n", glo_fMapped? "yes":"no" );
     fprintf( pAbc->Err, "\t-c     : toggle network check after reading [default = %s]\n", fCheck? "yes":"no" );
     fprintf( pAbc->Err, "\t-b     : toggle reading barrier buffers [default = %s]\n", fBarBufs? "yes":"no" );
+    fprintf( pAbc->Err, "\t-g     : toggle reading and flattening into &-space [default = %s]\n", fBarBufs? "yes":"no" );
     fprintf( pAbc->Err, "\t-h     : prints the command summary\n" );
     fprintf( pAbc->Err, "\tfile   : the name of a file to read\n" );
     return 1;
diff --git a/src/base/io/ioUtil.c b/src/base/io/ioUtil.c
index 24ed029a..671c6d56 100644
--- a/src/base/io/ioUtil.c
+++ b/src/base/io/ioUtil.c
@@ -158,7 +158,19 @@ Abc_Ntk_t * Io_ReadNetlist( char * pFileName, Io_FileType_t FileType, int fCheck
         return NULL;
     }
     if ( Abc_NtkBlackboxNum(pNtk) || Abc_NtkWhiteboxNum(pNtk) )
+    {
+        int i, fCycle = 0;
+        Abc_Ntk_t * pModel;
         fprintf( stdout, "Warning: The network contains hierarchy.\n" );
+        Vec_PtrForEachEntry( Abc_Ntk_t *, pNtk->pDesign->vModules, pModel, i )
+                if ( !Abc_NtkIsAcyclicWithBoxes( pModel ) )
+                    fCycle = 1;
+        if ( fCycle )
+        {
+            Abc_NtkDelete( pNtk );
+            return NULL;    
+        }
+    }
     return pNtk;
 }