re PR target/47025 (Dead stores in variadic functions not eliminated)

re PR target/47025 (Dead stores in variadic functions not eliminated)

2011-09-06  Richard Guenther  <rguenther@suse.de>

	PR tree-optimization/47025
	* tree-ssa-alias.c (ref_maybe_used_by_call_p_1): BUILT_IN_VA_END
	uses nothing.
	(call_may_clobber_ref_p_1): BUILT_IN_VA_END is a barrier like
	BUILT_IN_FREE.
	(stmt_kills_ref_p_1): BUILT_IN_VA_END kills what its argument
	definitely points to.
	* tree-ssa-structalias.c (find_func_aliases_for_builtin_call):
	BUILT_IN_VA_START doesn't let its va_list argument escape.
	* tree-ssa-dce.c (propagate_necessity): BUILT_IN_VA_END does
	not make any previous stores necessary.

From-SVN: r178601