re PR tree-optimization/27639 (VRP miscompilation of simple loop)

re PR tree-optimization/27639 (VRP miscompilation of simple loop)

	PR tree-optimization/27639
	PR tree-optimization/26719
	* tree-vrp.c (adjust_range_with_scev): Use scev_direction and adjust
	call to scev_probably_wraps_p.
	* tree-ssa-loop-niter.c (compare_trees, convert_step_widening,
	used_in_pointer_arithmetic_p, convert_step): Removed.
	(nowrap_type_p): New function.
	(scev_probably_wraps_p): Rewritten.
	* tree-scalar-evolution.c (instantiate_parameters_1): Do not call
	chrec_convert if chrec_convert_aggressive might have been used.
	* tree-chrec.c (convert_affine_scev, chrec_convert_1,
	scev_direction): New functions.
	(chrec_convert): Changed to a wrapper over chrec_convert_1.
	* tree-ssa-loop-ivopts.c (idx_find_step): Use convert_affine_scev
	instead of convert_step.
	* tree-flow.h (scev_probably_wraps_p): Declaration changed.
	(convert_step): Declaration removed.
	(convert_affine_scev, nowrap_type_p, scev_direction): Declare.

	* gcc.dg/pr27639.c: New test.
	* gcc.dg/pr26719.c: New test.
	* gcc.dg/tree-ssa/scev-cast.c: New test.

From-SVN: r114057