lra: Don't remove the scratch in (mem:BLK (scratch))

LRA wants to replace SCRATCH registers with real registers.  It should
not do that with (mem:BLK (scratch)), which is special, not really a
scratch register.


2015-10-29  Segher Boessenkool  <segher@kernel.crashing.org>

	* lra-constraints.c (process_address_1): Handle (mem:BLK (scratch))
	by ignoring it.

From-SVN: r229551

gcc/ChangeLog

+2015-10-29  Segher Boessenkool  <segher@kernel.crashing.org>
+
+	* lra-constraints.c (process_address_1): Handle (mem:BLK (scratch))
+	by ignoring it.
+
 2015-10-29  Richard Henderson  <rth@redhat.com>
 
 	PR target/68124

gcc/lra-constraints.c

@@ -2874,6 +2874,11 @@ process_address_1 (int nop, bool check_only_p,
   enum constraint_num cn = lookup_constraint (constraint);
   bool change_p = false;
 
+  if (MEM_P (op)
+      && GET_MODE (op) == BLKmode
+      && GET_CODE (XEXP (op, 0)) == SCRATCH)
+    return false;
+
   if (insn_extra_address_constraint (cn))
     decompose_lea_address (&ad, curr_id->operand_loc[nop]);
   else if (MEM_P (op))