PR rtl-optimization/26244

	PR rtl-optimization/26244
	* cse.c (fold_rtx): Correctly associate shifts when const_arg1 and/or
	inner_const are negative or greater than or equal to the bitsize of
	MODE.  If SHIFT_COUNT_TRUNCATED is false, the values aren't associated.
	Otherwise, the values are masked using GET_MODE_BITSIZE (mode) - 1.
	Simplify complicated if statement.  For ASHIFT and LSHIFTRT, return
	CONST0_RTX (mode) when the new shift count is greater than or equal to
	to the bitsize of the object being shifted and XEXP (y, 0) has no side
	effects.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@115924 138bc75d-0d04-0410-961f-82ee72b054a4