re PR rtl-optimization/26244 (FAIL: gcc.c-torture/execute/builtin-bitops-1.c executio...

re PR rtl-optimization/26244 (FAIL: gcc.c-torture/execute/builtin-bitops-1.c execution,  -O3 -fomit-frame-pointer -funroll-loops)

	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.

Co-Authored-By: Roger Sayle <roger@eyesopen.com>
From-SVN: r115924