tree-optimization/114760 - check variants of >> and << in loop-niter

tree-optimization/114760 - check variants of >> and << in loop-niter

When recognizing bit counting idiom, include pattern "x * 2"
for "x << 1", and "x / 2" for "x >> 1" (given x is unsigned).

gcc/ChangeLog:
	PR tree-optimization/114760
	* tree-ssa-loop-niter.cc (is_lshift_by_1): New function
	to check if STMT is equivalent to x << 1.
	(is_rshift_by_1): New function to check if STMT is
	equivalent to x >> 1.
	(number_of_iterations_cltz): Enhance the identification
	of logical shift by one.
	(number_of_iterations_cltz_complement): Enhance the
	identification of logical shift by one.

gcc/testsuite/ChangeLog:
	PR tree-optimization/114760
	* gcc.dg/tree-ssa/pr114760-1.c: New test.
	* gcc.dg/tree-ssa/pr114760-2.c: New test.