Fix handling of unknown sizes in rtx_addr_can_trap_p

[Richard Sandiford]

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.

Tested on aarch64-linux-gnu and x86_64-linux-gnu.  OK to install?

Thanks,
Richard


[ This patch is part of the SVE series posted here:
  https://gcc.gnu.org/ml/gcc/2016-11/msg00030.html ]

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.

diff --git a/gcc/rtlanal.c b/gcc/rtlanal.c
index a9d3960..889b14d 100644
--- a/gcc/rtlanal.c
+++ b/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)
 	    {