tree-ssa-dse.c (valid_ao_ref_for_dse): Reject ao_refs with negative offsets.

	* tree-ssa-dse.c (valid_ao_ref_for_dse): Reject ao_refs with
	negative offsets.

From-SVN: r253691

gcc/ChangeLog

+2017-10-12  Jeff Law  <law@redhat.com>
+
+	* tree-ssa-dse.c (valid_ao_ref_for_dse): Reject ao_refs with
+	negative offsets.
+
 2017-10-12  Martin Sebor  <msebor@redhat.com>
 
 	PR other/82301

gcc/tree-ssa-dse.c

@@ -131,6 +131,7 @@ valid_ao_ref_for_dse (ao_ref *ref)
 	  && ref->max_size != -1
 	  && ref->size != 0
 	  && ref->max_size == ref->size
+	  && ref->offset >= 0
 	  && (ref->offset % BITS_PER_UNIT) == 0
 	  && (ref->size % BITS_PER_UNIT) == 0
 	  && (ref->size != -1));