possible negative patch for gcc/tree-ssa-loop-im.c (or removal of an assert)

[Gaius Mulley]

Hello,

I've been looking through tree-ssa-loop-im.c (while hunting down a bug
in the modula-2 front end) and found a curiosity in
gcc/tree-ssa-loop-im.c.

It seems that there is dead code in function determine_max_movement
as mem_ref_in_stmt can never return NULL.


static mem_ref_p
mem_ref_in_stmt (gimple stmt)
{
  ...

  gcc_assert (ref != NULL);
  return ref;
}

so the patch below could logically be applied as the else statement is
currently unreachable.



--- tree-ssa-loop-im.c.orig     2014-07-11 16:54:41.000000000 +0100
+++ tree-ssa-loop-im.c  2014-07-11 16:55:38.000000000 +0100
@@ -798,21 +798,11 @@
     {
       mem_ref_p ref = mem_ref_in_stmt (stmt);
 
-      if (ref)
-       {
-         lim_data->max_loop
-                 = outermost_indep_loop (lim_data->max_loop, loop, ref);
-         if (!lim_data->max_loop)
-           return false;
-       }
-      else
-       {
-         if ((val = gimple_vuse (stmt)) != NULL_TREE)
-           {
-             if (!add_dependency (val, lim_data, loop, false))
-               return false;
-           }
-       }
+      gcc_assert (ref != NULL);
+      lim_data->max_loop
+       = outermost_indep_loop (lim_data->max_loop, loop, ref);
+      if (!lim_data->max_loop)
+       return false;
     }
 
   lim_data->cost += stmt_cost (stmt);


However my question is whether the assert in mem_ref_in_stmt is correct?
Since the author of determine_max_movement must have thought ref could
be NULL.

Anyhow, it seems that either the above patch should be applied or the
'gcc_assert (ref != NULL);' from mem_ref_p should be removed.

regards,
Gaius