* varpool.c (dump_varpool_node): Dump write-only flag.
	* lto-cgraph.c (lto_output_varpool_node, input_varpool_node): Stream
	write-only flag.
	* tree-cfg.c (execute_fixup_cfg): Remove statements setting write-only variables.


	* gcc.c-torture/execute/20101011-1.c: Update testcase.
	* gcc.dg/ira-shrinkwrap-prep-1.c: Update testcase.
	* gcc.dg/tree-ssa/writeonly.c: New testcase.
	* gcc.dg/tree-ssa/ssa-dse-6.c: Update testcase.
	* gcc.dg/tree-ssa/pr21559.c: Update testcase.
	* gcc.dg/debug/pr35154.c: Update testcase.
	* gcc.target/i386/vectorize1.c: Update testcase.
	* ipa.c (process_references): New function.
	(set_readonly_bit): New function.
	(set_writeonly_bit): New function.
	(clear_addressable_bit): New function.
	(ipa_discover_readonly_nonaddressable_var): Mark write only variables; fix
	handling of aliases.
	* cgraph.h (struct varpool_node): Add writeonly flag.

From-SVN: r210522