PR tree-optimization/77975
	* tree-ssa-loop-niter.c (get_base_for): Allow phi argument from latch
	edge to be constant.
	(get_val_for): For constant x return it.  Formatting fix.
	(loop_niter_by_eval): Avoid pointless looping if the next iteration
	would use the same bases as the current one.

	* gcc.dg/pr77975.c: New test.

From-SVN: r246021