bb-reorder: Improve the simple algorithm for -Os (PR67864)

bb-reorder: Improve the simple algorithm for -Os (PR67864)

As the PR points out, the "simple" reorder algorithm makes bigger code
than the STC algorithm did, for -Os, for x86.  I now tested it for many
different targets and it turns out to be worse everywhere.

This simple patch tunes "simple" a bit; this makes it better than STC
almost everywhere.  The only exceptions (for the targets where I have
results) are x86 and mn10300.  For those targets it may be best to switch
the default algorithm for -Os to STC.

2015-10-11  Segher Boessenkool  <segher@kernel.crashing.org>

	PR rtl-optimization/67864
	* gcc/bb-reorder (reorder_basic_blocks_simple): Prefer existing
	fallthrough edges for conditional jumps.  Don't sort candidate
	edges if not optimizing for speed.

From-SVN: r228692