1) Add new new option flag_tree_fully_unroll_loop to control
     whether do completely loop unrolling in the phase of
     canonicalization of induction variables.
  2) Fix the code to pass the uninitialized var use in the build.

	modified:   gcc/common.opt
	modified:   gcc/tree-ssa-loop-ivcanon.c
	modified:   gcc/tree-ssa-loop-manip.c
	modified:   gcc/tree-vect-loop-manip.c
	modified:   gcc/tree-vect-loop.c
	modified:   gcc/tree-vectorizer.c