* combine.c (simplify_shift_const_1): Split code to determine
	shift_mode into ...
	(try_widen_shift_mode): ... here.  Allow widening for ASHIFTRT if the
	new bits shifted in are identical to the old sign bit.

testsuite/
	* gcc.target/mips/octeon-exts-7.c: New test.
	* gcc.target/mips/octeon-exts-2.c: Revert previous change.
	* gcc.target/mips/octeon-exts-5.c: Likewise.

From-SVN: r149778