Allow match-and-simplified phiopt to run in early phiopt

Allow match-and-simplified phiopt to run in early phiopt

To move a few things more to match-and-simplify from phiopt,
we need to allow match_simplify_replacement to run in early
phiopt. To do this we add a replacement for gimple_simplify
that is explictly for phiopt.

OK? Bootstrapped and tested on x86_64-linux-gnu with no
regressions.

gcc/ChangeLog:

	* tree-ssa-phiopt.c (match_simplify_replacement):
	Add early_p argument. Call gimple_simplify_phiopt
	instead of gimple_simplify.
	(tree_ssa_phiopt_worker): Update call to
	match_simplify_replacement and allow unconditionally.
	(phiopt_early_allow): New function.
	(gimple_simplify_phiopt): New function.