[PATCH] Cleanup TODO handling for CFG clenaup & SSA update

[Richard Biener]

There's an old comment

      /* When cleanup_tree_cfg merges consecutive blocks, it may
         perform some simplistic propagation when removing single
         valued PHI nodes.  This propagation may, in turn, cause the
         SSA form to become out-of-date (see PR 22037).  So, even
         if the parent pass had not scheduled an SSA update, we may
         still need to do one.  */
      if (!(flags & TODO_update_ssa_any) && need_ssa_update_p (cfun))
        flags |= TODO_update_ssa;

which is from times we've had multiple virtual operands.  After
those went away we could still run into this for example when
propagating a non-const function address into an indirect call
through a const function type.  This has been fixed as well
(we retain the const-ness of the call).  Thus the above is
no longer necessary and we can simplify the code.

Bootstrapped on x86_64-unknown-linux-gnu, testing in progress.

I'm not really nervous about this change but if you think it
should wait for GCC 10 speak up.

Richard.

2019-03-08  Richard Biener  <rguent...@suse.de>

        * passes.c (execute_function_todo): Remove dead code.

Index: gcc/passes.c
===================================================================
--- gcc/passes.c        (revision 269302)
+++ gcc/passes.c        (working copy)
@@ -1924,26 +1924,12 @@ execute_function_todo (function *fn, voi
 
   push_cfun (fn);
 
-  /* Always cleanup the CFG before trying to update SSA.  */
+  /* If we need to cleanup the CFG let it perform a needed SSA update.  */
   if (flags & TODO_cleanup_cfg)
-    {
-      cleanup_tree_cfg (flags & TODO_update_ssa_any);
-
-      /* When cleanup_tree_cfg merges consecutive blocks, it may
-        perform some simplistic propagation when removing single
-        valued PHI nodes.  This propagation may, in turn, cause the
-        SSA form to become out-of-date (see PR 22037).  So, even
-        if the parent pass had not scheduled an SSA update, we may
-        still need to do one.  */
-      if (!(flags & TODO_update_ssa_any) && need_ssa_update_p (cfun))
-       flags |= TODO_update_ssa;
-    }
-
-  if (flags & TODO_update_ssa_any)
-    {
-      unsigned update_flags = flags & TODO_update_ssa_any;
-      update_ssa (update_flags);
-    }
+    cleanup_tree_cfg (flags & TODO_update_ssa_any);
+  else if (flags & TODO_update_ssa_any)
+    update_ssa (flags & TODO_update_ssa_any);
+  gcc_assert (!need_ssa_update_p (fn));
 
   if (flag_tree_pta && (flags & TODO_rebuild_alias))
     compute_may_aliases ();