PR rtl-optimization/23567
	* ifcvt.c (noce_mem_write_may_trap_or_fault_p): New function.
	(noce_process_if_block): Don't do any optimizations except
	if (cond) x = x; if !set_b and write into orig_x may trap
	or fault.  Remove the MEM_READONLY_P check.

	* gcc.c-torture/execute/20051104-1.c: New test.

From-SVN: r106585