Tighten check for whether sibcall references local variables

Tighten check for whether sibcall references local variables

This loop:

      /* Make sure the tail invocation of this function does not refer
         to local variables.  */
      FOR_EACH_LOCAL_DECL (cfun, idx, var)
        {
          if (TREE_CODE (var) != PARM_DECL
              && auto_var_in_fn_p (var, cfun->decl)
              && (ref_maybe_used_by_stmt_p (call, var)
                  || call_may_clobber_ref_p (call, var)))
            return;
        }

triggered even for local variables that are passed by value.
This meant that we didn't allow local aggregates to be passed
to a sibling call but did (for example) allow global aggregates
to be passed.

I think the loop is really checking for indirect references,
so should be able to skip any variables that never have their
address taken.

gcc/
	* tree-tailcall.c (find_tail_calls): Allow calls to reference
	local variables if all references are known to be direct.

gcc/testsuite/
	* gcc.dg/tree-ssa/tailcall-8.c: New test.

From-SVN: r242860