tree-optimization/113374 - early break vect and virtual operands

tree-optimization/113374 - early break vect and virtual operands

The following fixes wrong virtual operands being used for peeled
early breaks where we can have different live ones and for multiple
exits it makes sure to update the correct PHI arguments.

I've introduced SET_PHI_ARG_DEF_ON_EDGE so we can avoid using
a wrong edge to compute the PHI arg index from.

I've took the liberty to understand the code again and refactor
and comment it a bit differently.  The main functional change
is that we preserve the live virtual operand on all exits.

	PR tree-optimization/113374
	* tree-ssa-operands.h (SET_PHI_ARG_DEF_ON_EDGE): New.
	* tree-vect-loop.cc (move_early_exit_stmts): Update
	virtual LC PHIs.
	* tree-vect-loop-manip.cc (slpeel_tree_duplicate_loop_to_edge_cfg):
	Refactor.  Preserve virtual LC PHIs on all exits.

	* gcc.dg/vect/vect-early-break_106-pr113374.c: New testcase.