tree-optimization/101267 - fix SLP vect with masked operations

tree-optimization/101267 - fix SLP vect with masked operations

This fixes the missed handling of external/constant mask SLP
operations, for the testcase in particular masked loads.  The
patch adjusts the vect_check_scalar_mask API to reflect the
required vect_is_simple_use SLP compatible API plus adjusts
for the special handling of masked loads in SLP discovery.

The issue is likely latent.

2021-06-30  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/101267
	* tree-vect-stmts.c (vect_check_scalar_mask): Adjust
	API and use SLP compatible interface of vect_is_simple_use.
	Reject not vectorized SLP defs for callers that do not support
	that.
	(vect_check_store_rhs): Handle masked stores and pass down
	the appropriate operator index.
	(vectorizable_call): Adjust.
	(vectorizable_store): Likewise.
	(vectorizable_load): Likewise.  Handle SLP pecularity of
	masked loads.
	(vect_is_simple_use): Remove special-casing of masked stores.

	* gfortran.dg/pr101267.f90: New testcase.