vect_analyze_loop_operations was calling vectorizable_live_operation
for all live-out phis, which led to a bogus ncopies calculation in
the pure SLP case.  I think v_a_l_o should only be passing phis
that are vectorised using normal loop vectorisation, since
vect_slp_analyze_node_operations handles the SLP side (and knows
the correct slp_index and slp_node arguments to pass in, via
vect_analyze_stmt).

With that fixed we hit an older bug that vectorizable_live_operation
didn't handle live-out SLP inductions.  Fixed by using gimple_phi_result
rather than gimple_get_lhs for phis.

2018-01-16  Richard Sandiford  <richard.sandiford@linaro.org>

gcc/
	PR tree-optimization/83857
	* tree-vect-loop.c (vect_analyze_loop_operations): Don't call
	vectorizable_live_operation for pure SLP statements.
	(vectorizable_live_operation): Handle PHIs.

gcc/testsuite/
	PR tree-optimization/83857
	* gcc.dg/vect/pr83857.c: New test.

From-SVN: r256747