tree-optimization/101505 - properly determine stmt precision for PHIs

tree-optimization/101505 - properly determine stmt precision for PHIs

Loop vectorization pattern recog fails to walk PHIs when determining
stmt precisions.  This fails to recognize non-mask uses for bools
in PHIs and outer loop vectorization.

2021-07-19  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/101505
	* tree-vect-patterns.c (vect_determine_precisions): Walk
	PHIs also for loop vectorization.

	* gcc.dg/vect/pr101505.c: New testcase.

(cherry picked from commit 8df3ee8f7d85d0708f3c3ca96b55c9230c2ae9f0)