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

4 files changed, 93 insertions, 2 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index f2b4828..efc2016 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,8 @@
+2016-11-25  Richard Sandiford  <richard.sandiford@arm.com>
+
+	* tree-tailcall.c (find_tail_calls): Allow calls to reference
+	local variables if all references are known to be direct.
+
 2016-11-25  Jakub Jelinek  <jakub@redhat.com>
 	    Prathamesh Kulkarni  <prathamesh.kulkarni@linaro.org>
 
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 1028191..e18397f 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,7 @@
+2016-11-25  Richard Sandiford  <richard.sandiford@arm.com>
+
+	* gcc.dg/tree-ssa/tailcall-8.c: New test.
+
 2016-11-25  Senthil Kumar Selvaraj  <senthil_kumar.selvaraj@atmel.com>
 
 	* gcc.dg/pr64277.c: Use __INT32_TYPE__ for targets
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/tailcall-8.c b/gcc/testsuite/gcc.dg/tree-ssa/tailcall-8.c
new file mode 100644
index 0000000..ffeabe5
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/tailcall-8.c
@@ -0,0 +1,80 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-tailc-details" } */
+
+struct s { int x; };
+void f_direct (struct s);
+void f_indirect (struct s *);
+void f_void (void);
+
+/* Tail call.  */
+void
+g1 (struct s param)
+{
+  f_direct (param);
+}
+
+/* Tail call.  */
+void
+g2 (struct s *param_ptr)
+{
+  f_direct (*param_ptr);
+}
+
+/* Tail call.  */
+void
+g3 (struct s *param_ptr)
+{
+  f_indirect (param_ptr);
+}
+
+/* Tail call.  */
+void
+g4 (struct s *param_ptr)
+{
+  f_indirect (param_ptr);
+  f_void ();
+}
+
+/* Tail call.  */
+void
+g5 (struct s param)
+{
+  struct s local = param;
+  f_direct (local);
+}
+
+/* Tail call.  */
+void
+g6 (struct s param)
+{
+  struct s local = param;
+  f_direct (local);
+  f_void ();
+}
+
+/* Not a tail call.  */
+void
+g7 (struct s param)
+{
+  struct s local = param;
+  f_indirect (&local);
+}
+
+/* Not a tail call.  */
+void
+g8 (struct s *param_ptr)
+{
+  struct s local = *param_ptr;
+  f_indirect (&local);
+}
+
+/* Not a tail call.  */
+void
+g9 (struct s *param_ptr)
+{
+  struct s local = *param_ptr;
+  f_indirect (&local);
+  f_void ();
+}
+
+/* { dg-final { scan-tree-dump-times "Found tail call" 6 "tailc" } } */
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;