combine: Allow combining two insns to two insns

combine: Allow combining two insns to two insns

This patch allows combine to combine two insns into two.  This helps
in many cases, by reducing instruction path length, and also allowing
further combinations to happen.  PR85160 is a typical example of code
that it can improve.

This patch does not allow such combinations if either of the original
instructions was a simple move instruction.  In those cases combining
the two instructions increases register pressure without improving the
code.  With this move test register pressure does no longer increase
noticably as far as I can tell.

(At first I also didn't allow either of the resulting insns to be a
move instruction.  But that is actually a very good thing to have, as
should have been obvious).

	PR rtl-optimization/85160
	* combine.c (is_just_move): New function.
	(try_combine): Allow combining two instructions into two if neither of
	the original instructions was a move.

From-SVN: r263067