Re: [PATCH] Fix ARM constant-pool layout calculations under -falign-labels

[Julian Brown <julian at codesourcery dot com>]

On Wed, 1 Aug 2012 14:43:33 -0700
Roland McGrath <mcgrathr@google.com> wrote:

> Using e.g. -falign-labels=16 on ARM can confuse the constant-pool
> layout code such that it places pool entries too far away from their
> referring instructions.  This change seems to fix it.
> 
> I don't have a small test case, only a large one, which I haven't
> actually tried to get to reproduce on any vanilla ARM target.  But
> the logic of the change seems straightforward and sound.

FWIW, I've hit this issue in the past, and used a patch as follows to
fix it:

@@ -12015,7 +12025,10 @@ create_fix_barrier (Mfix *fix, HOST_WIDE
       gcc_assert (GET_CODE (from) != BARRIER);
 
       /* Count the length of this insn.  */
-      count += get_attr_length (from);
+      if (LABEL_P (from) && (align_jumps > 0 || align_loops > 0))
+        count += MAX (align_jumps, align_loops);
+      else
+        count += get_attr_length (from);
 
       /* If there is a jump table, add its length.  */
       tmp = is_jump_table (from);
@@ -12435,6 +12448,8 @@ arm_reorg (void)
              insn = table;
            }
        }
+      else if (LABEL_P (insn) && (align_jumps > 0 || align_loops > 0))
+       address += MAX (align_jumps, align_loops);
     }
 
   fix = minipool_fix_head;

Not sure if that's equivalent, but you might want to check
-falign-jumps too while you're at it.

Cheers,

Julian