ifcvt.c (dead_or_predicable): Use df_simulate_find_defs and df_simulate_find_noclobber_defs as appropriate.

	* ifcvt.c (dead_or_predicable): Use df_simulate_find_defs and
	df_simulate_find_noclobber_defs as appropriate.  Keep track of an
	extra set merge_set_noclobber, and use it to relax the final test
	slightly.
	* df.h (df_simulate_find_noclobber_defs): Declare.
	* df-problems.c (df_simulate_find_defs): Don't ignore partial or
	conditional defs.
	(df_simulate_find_noclobber_defs): New function.

From-SVN: r158639