re PR tree-optimization/71588 (ICE on valid code at -O2 and -O3 on x86_64-linux-gnu: in execute_todo, at passes.c:2009)

	PR tree-optimization/71588
	* tree-ssa-strlen.c (valid_builtin_call): New function.
	(adjust_last_stmt, handle_builtin_memset, strlen_optimize_stmt): Use
	it.

	* gcc.dg/pr71558.c: New test.

From-SVN: r237628