tree-ssa-strlen: optimization skips clobbering store [PR111519]

The following testcase is miscompiled, because count_nonzero_bytes incorrectly
uses get_strinfo information on a pointer from which an earlier instruction
loads SSA_NAME stored at the current instruction.  get_strinfo shows a state
right before the current store though, so if there are some stores in between
the current store and the load, the string length information might have
changed.

The patch passes around gimple_vuse from the store and punts instead of using
strinfo on loads from MEM_REF which have different gimple_vuse from that.

2023-10-11  Richard Biener  <rguenther@suse.de>
	    Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/111519
	* tree-ssa-strlen.cc (strlen_pass::count_nonzero_bytes): Add vuse
	argument and pass it through to recursive calls and
	count_nonzero_bytes_addr calls.  Don't shadow the stmt argument, but
	change stmt for gimple_assign_single_p statements for which we don't
	immediately punt.
	(strlen_pass::count_nonzero_bytes_addr): Add vuse argument and pass
	it through to recursive calls and count_nonzero_bytes calls.  Don't
	use get_strinfo if gimple_vuse (stmt) is different from vuse.  Don't
	shadow the stmt argument.

	* gcc.dg/torture/pr111519.c: New testcase.