PR tree-optimization/89500

	PR tree-optimization/89500
	* tree-ssa-strlen.c (stridx_strlenloc): Adjust comment.
	(handle_builtin_strlen): Remove noncst_bound variable.  Always
	optimize strnlen (x, 0) to 0.  Optimize strnlen (x, cst) to
	cst if the first cst bytes starting at x are known to be non-zero,
	even if the string is not zero terminated.  Don't try to modify
	*si for strnlen.  Update strlen_to_stridx only for strlen or if
	we can prove strnlen returns the same value as strlen would.

	* gcc.dg/pr89500.c: New test.
	* gcc.dg/Wstringop-overflow-10.c: New test.
	* gcc.dg/strlenopt-60.c: New test.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@269230 138bc75d-0d04-0410-961f-82ee72b054a4