When niter may be zero, return a COND_EXPR with the may_be_zero condition.

2010-05-28  Sebastian Pop  <sebastian.pop@amd.com>

	* tree-scalar-evolution.c (set_nb_iterations_in_loop): Inlined in the
	only place it was called from.
	(number_of_latch_executions): Do not return chrec_dont_know when the
	may_be_zero is a runtime condition: instead, return a COND_EXPR
	including the may_be_zero condition.
	* cfgloop.h (struct loop): Add a note on COND_EXPRs to the comment
	of nb_iterations.
	* tree-ssa-loop-ivopts.c (contains_abnormal_ssa_name_p): Handle
	COND_EXPRs.

	* gcc.dg/vect/vect-outer-fir-lb.c: Un-XFAIL-ed.

From-SVN: r159992