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

1 files changed, 4 insertions, 2 deletions

diff --git a/gcc/tree-tailcall.c b/gcc/tree-tailcall.c
index f97541d..66a0a4c 100644
--- a/gcc/tree-tailcall.c
+++ b/gcc/tree-tailcall.c
@@ -504,12 +504,14 @@ find_tail_calls (basic_block bb, struct tailcall **ret)
 	tail_recursion = true;
     }
 
-  /* Make sure the tail invocation of this function does not refer
-     to local variables.  */
+  /* Make sure the tail invocation of this function does not indirectly
+     refer to local variables.  (Passing variables directly by value
+     is OK.)  */
   FOR_EACH_LOCAL_DECL (cfun, idx, var)
     {
       if (TREE_CODE (var) != PARM_DECL
 	  && auto_var_in_fn_p (var, cfun->decl)
+	  && may_be_aliased (var)
 	  && (ref_maybe_used_by_stmt_p (call, var)
 	      || call_may_clobber_ref_p (call, var)))
 	return;