This patch fixes an exponential issue in ccmp.c.  When deciding which ccmp
expansion to use, the tree nodes gs0 and gs1 are fully expanded twice.  If
they contain more CCMP opportunities, their subtrees are also expanded twice.
When the trees are complex the expansion takes exponential time and memory.
As a workaround in GCC6 compute the cost of the first expansion early, and
only try the alternative expansion if the cost is low enough.  This rarely
affects real code, eg. SPECINT2006 has identical codesize.

2016-02-04  Wilco Dijkstra  <wdijkstr@arm.com>

    gcc/
	PR target/69619
	* ccmp.c (expand_ccmp_expr_1): Avoid evaluating gs0/gs1
	twice when complex.

    gcc/testsuite/
	PR target/69619
	* gcc.dg/pr69619.c: Add new test.

From-SVN: r233145