diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index a49e0249236..fe32d0f7d31 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2016-11-16  Richard Sandiford  <richard.sandiford@arm.com>
+	    Alan Hayward  <alan.hayward@arm.com>
+	    David Sherwood  <david.sherwood@arm.com>
+
+	* cprop.c (local_cprop_find_used_regs): Use df_read_modify_subreg_p.
+
 2016-11-16  Richard Biener  <rguenther@suse.de>
 
 	PR middle-end/78333
diff --git a/gcc/cprop.c b/gcc/cprop.c
index 6b4c0b8fa38..31868a5c6bb 100644
--- a/gcc/cprop.c
+++ b/gcc/cprop.c
@@ -1161,9 +1161,7 @@ local_cprop_find_used_regs (rtx *xptr, void *data)
       return;
 
     case SUBREG:
-      /* Setting a subreg of a register larger than word_mode leaves
-	 the non-written words unchanged.  */
-      if (GET_MODE_BITSIZE (GET_MODE (SUBREG_REG (x))) > BITS_PER_WORD)
+      if (df_read_modify_subreg_p (x))
 	return;
       break;