tree-optimization/122723 - masking of .COND_ADD reductions

tree-optimization/122723 - masking of .COND_ADD reductions

The following fixes loop masking of .COND_ADD reductions when
we decide to reduce multiple lanes to one, thus go through
vect_transform_reduction.  The first issue is in
vect_reduction_update_partial_vector_usage which does not handle
incoming .COND_ADD well and fails to compute 'cond_fn' in this
case, disabling masking.  The second issue is that
vect_transform_reduction does not implement the masked but
not mask-by-cond case for any .COND_* operation.  The following
should fix both.

The testcases verify runtime in vect.exp and vectorization support
in the i386 target section for the combinations of -O3, -Ofast
plus masked vs. non-masked epilogues.

	PR tree-optimization/122723
	* tree-vect-loop.cc (vect_reduction_update_partial_vector_usage):
	Handle incoming .COND_* operation.
	(vect_transform_reduction): Likewise.  Handle .COND_*
	operation when not using COND_EXPR masking in a masked loop.

	* gcc.dg/vect/vect-reduc-cond-add-1.c: New generic functional
	testcase.
	* gcc.target/i386/vect-epilogues-6.c: New testcase.
	* gcc.target/i386/vect-epilogues-7.c: Likewise.
	* gcc.target/i386/vect-epilogues-8.c: Likewise.
	* gcc.target/i386/vect-epilogues-9.c: Likewise.