Fix handling of unknown sizes in rtx_addr_can_trap_p

If the size passed in to rtx_addr_can_trap_p was zero, the frame
handling would get the size from the mode instead.  However, this
too can be zero if the mode is BLKmode, i.e. if we have a BLKmode
memory reference with no MEM_SIZE (which should be rare these days).
This meant that the conditions for a 4-byte access at offset X were
stricter than those for an access of unknown size at offset X.

This patch checks whether the size is still zero, as the
SYMBOL_REF handling does.

gcc/
2016-11-15  Richard Sandiford  <richard.sandiford@arm.com>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

	* rtlanal.c (rtx_addr_can_trap_p_1): Handle unknown sizes.

Co-Authored-By: Alan Hayward <alan.hayward@arm.com>
Co-Authored-By: David Sherwood <david.sherwood@arm.com>

From-SVN: r242476

gcc/ChangeLog

@@ -2,6 +2,12 @@
 	    Alan Hayward  <alan.hayward@arm.com>
 	    David Sherwood  <david.sherwood@arm.com>
 
+	* rtlanal.c (rtx_addr_can_trap_p_1): Handle unknown sizes.
+
+2016-11-16  Richard Sandiford  <richard.sandiford@arm.com>
+	    Alan Hayward  <alan.hayward@arm.com>
+	    David Sherwood  <david.sherwood@arm.com>
+
 	* tree-vect-loop.c (vect_transform_loop): Protect the updates of
 	all three iteration counts with an any_* test.  Use a single update
 	for each count.  Fix the calculation of nb_iterations_estimate.

gcc/rtlanal.c

@@ -543,6 +543,8 @@ rtx_addr_can_trap_p_1 (const_rtx x, HOST_WIDE_INT offset, HOST_WIDE_INT size,
 
 	  if (size == 0)
 	    size = GET_MODE_SIZE (mode);
+	  if (size == 0)
+	    return 1;
 
 	  if (x == frame_pointer_rtx)
 	    {