Fix SLP def type when computing masks (PR85853)

Fix SLP def type when computing masks (PR85853)

In this PR, SLP failed to include a comparison node in the SLP
tree and so marked the node as external.  It then went on to call
vect_is_simple_use on the comparison with its STMT_VINFO_DEF_TYPE
still claiming that it was an internal definition.

We already avoid that for vect_analyze_stmt by temporarily copying
the node's definition type to each STMT_VINFO_DEF_TYPE.  This patch
extends that to the vector type calculation.  The easiest thing
seemed to be to split the analysis of the root node out into
a subroutine, so that it's possible to return false early without
awkward control flow.

2018-05-23  Richard Sandiford  <richard.sandiford@linaro.org>

gcc/
	PR tree-optimization/85853
	* tree-vect-slp.c (vect_slp_analyze_node_operations): Split out
	the handling of the root of the node to...
	(vect_slp_analyze_node_operations_1): ...this new function,
	and run the whole thing with the child nodes' def types
	set according to their SLP node's def type.

gcc/testsuite/
	PR tree-optimization/85853
	* gfortran.dg/vect/pr85853.f90: New test.

From-SVN: r260601