tree-optimization/107919 - predicate simplification in uninit

tree-optimization/107919 - predicate simplification in uninit

The testcase from the PR at -O2 shows

    ((_277 == 2) AND (_79 == 0))
    OR ((NOT (_277 == 0)) AND (NOT (_277 > 2)) AND (NOT (_277 == 2)) AND (_79 == 0))
    OR ((NOT (pretmp_300 == 255)) AND (_277 == 0) AND (NOT (_277 > 2)) AND (NOT (_277 == 2)) AND (_79 == 0))

which we fail to simplify.  The following patch makes us simplify
the relations on _277, producing

    ((_79 == 0) AND (_277 == 2))
    OR ((_79 == 0) AND (_277 <= 1) AND (NOT (_277 == 0)))
    OR ((_79 == 0) AND (_277 == 0) AND (NOT (pretmp_300 == 255)))

which might be an incremental step to resolve a bogus uninit
diagnostic at -O2.  The patch uses maybe_fold_and_comparison for this.

	PR tree-optimization/107919
	* gimple-predicate-analysis.cc (simplify_1): Rename to ...
	(simplify_1a): .. this.
	(simplify_1b): New.
	(predicate::simplify): Call both simplify_1a and simplify_1b.