Improve match_simplify_replacement in phi-opt

Improve match_simplify_replacement in phi-opt

This improves match_simplify_replace in phi-opt to handle the
case where there is one cheap (non-call) preparation statement in the
middle basic block similar to xor_replacement and others.
This allows to remove xor_replacement which it does too.

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

Thanks,
Andrew Pinski

Changes since v1:
v3 - Just minor changes to using gimple_assign_lhs
instead of gimple_lhs and fixing a comment.
v2 - change the check on the preparation statement to
allow only assignments and no calls and only assignments
that feed into the phi.

gcc/ChangeLog:

	PR tree-optimization/25290
	* tree-ssa-phiopt.c (xor_replacement): Delete.
	(tree_ssa_phiopt_worker): Delete use of xor_replacement.
	(match_simplify_replacement): Allow one cheap preparation
	statement that can be moved to before the if.

gcc/testsuite/ChangeLog:

	* gcc.dg/tree-ssa/pr96928-1.c: Fix testcase for now that ~
	happens on the outside of the bit_xor.