* cfgloop.h (struct loop): New field constraints.
	(LOOP_C_INFINITE, LOOP_C_FINITE): New macros.
	(loop_constraint_set, loop_constraint_clr, loop_constraint_set_p): New
	functions.
	* cfgloop.c (alloc_loop): Initialize new field.
	* cfgloopmanip.c (copy_loop_info): Copy constraints.
	* tree-ssa-loop-niter.c (number_of_iterations_exit_assumptions):
	Adjust niter analysis wrto loop constraints.
	* doc/loop.texi (@node Number of iterations): Add description for loop
	constraints.

From-SVN: r238876