analyzer: fix ICE due to sm-state origin being purged (PR 93382)

The ICE in PR analyzer/93382 is a validation error.

The global variable "idx" acquires a "tainted" state from local array
n1[0].  When the frame is popped, the svalue for n1[0] is purged, but
the "taint" sm_state_map's entry for "idx" has a svalue_id referencing
the now-purged svalue.  This is caught by program_state::validate as an
assertion failure.

This patch fixes the issue by resetting the origin id within
sm_state_map entries for the case where the origin id has been purged.

gcc/analyzer/ChangeLog:
	PR analyzer/93382
	* program-state.cc (sm_state_map::on_svalue_purge): If the
	entry survives, but the origin is being purged, then reset the
	origin to null.

gcc/testsuite/ChangeLog:
	PR analyzer/93382
	* gcc.dg/analyzer/pr93382.c: New test.

gcc/analyzer/ChangeLog

 2020-01-22  David Malcolm  <dmalcolm@redhat.com>
 
+	PR analyzer/93382
+	* program-state.cc (sm_state_map::on_svalue_purge): If the
+	entry survives, but the origin is being purged, then reset the
+	origin to null.
+
+2020-01-22  David Malcolm  <dmalcolm@redhat.com>
+
 	* sm-signal.cc: Fix nesting of CHECKING_P and namespace ana.
 
 2020-01-22  David Malcolm  <dmalcolm@redhat.com>

gcc/analyzer/program-state.cc

@@ -453,6 +453,11 @@ sm_state_map::on_svalue_purge (const state_machine &sm,
 
 	  to_remove.safe_push (dst_sid);
 	}
+      else if ((*iter).second.m_origin.as_int () >= first_unused_sid.as_int ())
+	{
+	  /* If the origin svalue is being purged, then reset it to null.  */
+	  (*iter).second.m_origin = svalue_id::null ();
+	}
     }
 
   int i;

gcc/testsuite/ChangeLog

+2020-01-22  David Malcolm  <dmalcolm@redhat.com>
+
+	PR analyzer/93382
+	* gcc.dg/analyzer/pr93382.c: New test.
+
 2020-01-22  Andrew Pinski  <apinski@marvell.com>
 
 	* gcc.dg/tree-ssa/pr88497-1.c: Move to ...

gcc/testsuite/gcc.dg/analyzer/pr93382.c

+typedef __SIZE_TYPE__ size_t;
+
+int idx;
+void *fp;
+
+size_t
+fread (void *, size_t, size_t, void *);
+
+void
+ql (void)
+{
+  int n1[1];
+
+  fread (n1, sizeof (n1[0]), 1, fp); /* { dg-message "'n1' gets an unchecked value here" } */
+  idx = n1[0]; /* { dg-message "'idx' has an unchecked value here (from 'n1')" */
+}
+
+int arr[10];
+	
+int
+pl (void)
+{
+  ql ();
+  return arr[idx]; /* { dg-warning "use of tainted value 'idx' in array lookup without bounds checking" } */
+}