Merge pull request #7946 from donn/dft_null_ptr_access

dft: fix null pointer access

Author: maliberty

src/dft/src/cells/ScanCellFactory.cpp

@@ -60,7 +60,8 @@ TypeOfCell IdentifyCell(odb::dbInst* inst, sta::dbSta* sta)
   sta::dbNetwork* db_network = sta->getDbNetwork();
   sta::LibertyCell* liberty_cell
       = GetLibertyCell(inst->getMaster(), db_network);
-  if (liberty_cell->hasSequentials() && !inst->getMaster()->isBlock()) {
+  if (liberty_cell != nullptr && liberty_cell->hasSequentials()
+      && !inst->getMaster()->isBlock()) {
     // we assume that we are only dealing with one bit cells, but in the future
     // we could deal with multibit cells too
     return TypeOfCell::kOneBitCell;

src/dft/test/max_chain_count_sky130.ok

@@ -1,5 +1,6 @@
 [INFO ODB-0227] LEF file: sky130hd/sky130hd.tlef, created 13 layers, 25 vias
 [INFO ODB-0227] LEF file: sky130hd/sky130_fd_sc_hd_merged.lef, created 437 library cells
+[WARNING ORD-2011] LEF master sky130_fd_sc_hd__tapvpwrvgnd_1 has no liberty cell.
 ***************************
 Report DFT Plan
 Number of chains: 1

src/dft/test/max_chain_count_sky130.v

@@ -25,6 +25,8 @@ module max_chain_count(port1,
   output output9;
   output output10;
 
+  // A cell without a lib view to ensure those don't cause a crash
+  sky130_fd_sc_hd__tapvpwrvgnd_1 tap();
 
   // Rising edge flops
   sky130_fd_sc_hd__dfstp_1 ff1_clk1_rising(

src/dft/test/max_chain_count_sky130.vok

@@ -84,6 +84,7 @@ module max_chain_count (clock,
     .SCE(scan_enable_0),
     .SET_B(set_b),
     .CLK(clock));
+ sky130_fd_sc_hd__tapvpwrvgnd_1 tap ();
  sky130_fd_sc_hd__sdfsbp_1 ff10_clk1_rising (.D(port1),
     .Q(output10),
     .SCD(output1),