read_saif ref missing instance resolves #406

Signed-off-by: James Cherry <cherry@parallaxsw.com>

power/SaifReader.cc

@@ -139,7 +139,9 @@ SaifReader::instancePush(const char *instance_name)
   else {
     // Inside annotation scope.
     Instance *parent = path_.empty() ? sdc_network_->topInstance() : path_.back();
-    Instance *child = sdc_network_->findChild(parent, instance_name);
+    Instance *child = parent
+      ? sdc_network_->findChild(parent, instance_name)
+      : nullptr;
     path_.push_back(child);
   }
   stringDelete(instance_name);

test/read_saif_null_instance.lib

@@ -0,0 +1,14 @@
+library(min) {
+  technology(cmos);
+  time_unit : "1ns";
+  voltage_unit : "1V";
+  current_unit : "1mA";
+  capacitive_load_unit(1, pf);
+  cell(BUF) {
+    pin(A) { direction : input; }
+    pin(Y) { direction : output;
+      function : "A";
+      timing() { related_pin : "A"; }
+    }
+  }
+}

test/read_saif_null_instance.ok

@@ -0,0 +1 @@
+Annotated 0 pin activities.

test/read_saif_null_instance.saif

@@ -0,0 +1,16 @@
+(SAIFILE
+(SAIFVERSION "2.0")
+(DIRECTION "backward")
+(DIVIDER / )
+(TIMESCALE 1ns)
+(DURATION 1000)
+ (INSTANCE TOP
+  (INSTANCE child
+   (INSTANCE grandchild
+    (NET
+     (clk (T0 500) (T1 500) (TZ 0) (TX 0) (TB 0) (TC 1000))
+    )
+   )
+  )
+ )
+)

test/read_saif_null_instance.tcl

@@ -0,0 +1,5 @@
+# read_saif references missing instance
+read_liberty read_saif_null_instance.lib
+read_verilog read_saif_null_instance.v
+link_design top
+read_saif -scope TOP read_saif_null_instance.saif

test/read_saif_null_instance.v

@@ -0,0 +1,2 @@
+module top(input clk);
+endmodule

test/regression_vars.tcl

@@ -158,6 +158,7 @@ record_public_tests {
   path_group_names
   power_json
   prima3
+  read_saif_null_instance
   report_checks_sorted
   report_checks_src_attr
   report_json1