tree-optimization/105198 - wrong code with predictive commoning

tree-optimization/105198 - wrong code with predictive commoning

When predictive commoning looks for a looparound PHI it tries
to match the entry value definition (a load) up with the appropriate
member of the chain.  But it fails to consider stmts clobbering
the very same memory location inbetween the load and loop entry.

In theory we could be more clever on must aliases that would be
also picked up from a load (so not exactly stmt_kills_ref_p) and
use the stored value from that if it is an exact match.  But we
currently have no way to propagate this information inside predcom.

2022-04-08  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/105198
	* tree-predcom.c (find_looparound_phi): Check whether
	the found memory location of the entry value is clobbered
	inbetween the value we want to use and loop entry.

	* gcc.dg/torture/pr105198.c: New testcase.

(cherry picked from commit e5453bcc217ea4ac53a4ac277661d6ef0ccd425b)