optabs: Fix vec_perm -> V16QI middle end lowering.

The current implementation re-uses the location of the selection
pattern to generate a new one.  This fails if the pattern resides in a
read-only location.

gcc/
	* optabs.c (expand_vec_perm): Don't re-use SEL as target operand.

From-SVN: r223369

gcc/ChangeLog

 2015-05-19  Andreas Krebbel  <krebbel@linux.vnet.ibm.com>
 
+	* optabs.c (expand_vec_perm): Don't re-use SEL as target operand.
+
+2015-05-19  Andreas Krebbel  <krebbel@linux.vnet.ibm.com>
+
 	* config/s390/s390.c (s390_secondary_reload): Fix check for
 	load/store relative.
 

gcc/optabs.c

@@ -6777,11 +6777,11 @@ expand_vec_perm (machine_mode mode, rtx v0, rtx v1, rtx sel, rtx target)
       machine_mode selmode = GET_MODE (sel);
       if (u == 2)
 	sel = expand_simple_binop (selmode, PLUS, sel, sel,
-				   sel, 0, OPTAB_DIRECT);
+				   NULL, 0, OPTAB_DIRECT);
       else
 	sel = expand_simple_binop (selmode, ASHIFT, sel,
 				   GEN_INT (exact_log2 (u)),
-				   sel, 0, OPTAB_DIRECT);
+				   NULL, 0, OPTAB_DIRECT);
       gcc_assert (sel != NULL);
 
       /* Broadcast the low byte each element into each of its bytes.  */