re PR rtl-optimization/58997 (ICE on valid code at -O3 on x86_64-linux-gnu (affecting gcc trunk and 4.8.2))

	PR rtl-optimization/58997
	* loop-iv.c (iv_subreg): For IV_UNKNOWN_EXTEND, expect
	get_iv_value to be in iv->mode rather than iv->extend_mode.
	(iv_extend): Likewise.  Otherwise, if iv->extend != extend,
	use lowpart_subreg on get_iv_value before calling simplify_gen_unary.
	* loop-unswitch.c (may_unswitch_on): Make sure op[i] is in the right
	mode.

	* gcc.c-torture/compile/pr58997.c: New test.

From-SVN: r204413