tree-optimization/101801 - remove vect_worthwhile_without_simd_p

tree-optimization/101801 - remove vect_worthwhile_without_simd_p

This removes the cost part of vect_worthwhile_without_simd_p, retaining
only the correctness bits.  The reason is that the cost heuristic
do not properly account for SLP plus the check whether "without simd"
applies misfires for AVX512 mask vectors at the moment, leading to
missed vectorizations there.

Any costing decision should take place in the cost modeling, no
single stmt is to disable all vectorization on its own.

2021-08-06  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/101801
	* tree-vectorizer.h (vect_worthwhile_without_simd_p): Rename...
	(vect_can_vectorize_without_simd_p): ... to this.
	* tree-vect-loop.c (vect_worthwhile_without_simd_p): Rename...
	(vect_can_vectorize_without_simd_p): ... to this and fold
	in vect_min_worthwhile_factor.
	(vect_min_worthwhile_factor): Remove.
	(vectorizable_reduction): Adjust and remove the cost part.
	* tree-vect-stmts.c (vectorizable_shift): Likewise.
	(vectorizable_operation): Likewise.