[PATCH] bb-reorder: Improve compgotos pass (PR71785)

[Steven Bosscher]

On Sun, Oct 30, 2016 at 8:10 PM, Segher Boessenkool wrote:
> This patch solves this problem by simply running the duplicate_computed_gotos
> pass again, as long as it does any work.  The patch looks much bigger than
> it is, because I factored out two routines to simplify the control flow.

It's made the patch a bit difficult to read. Condensing it a bit...

> +  for (;;)
>      {
> +      if (n_basic_blocks_for_fn (fun) <= NUM_FIXED_BLOCKS + 1)
> +       return 0;

This test should not be needed in the loop. This pass can never
collapse the function to a single basic block.


> +      clear_bb_flags ();
> +      cfg_layout_initialize (0);

See comment below...


> +      basic_block bb;
> +      FOR_EACH_BB_FN (bb, fun)
> +       {
> +         /* Build the reorder chain for the original order of blocks.  */
> +         if (bb->next_bb != EXIT_BLOCK_PTR_FOR_FN (fun))
> +           bb->aux = bb->next_bb;
> +       }
>
> +      duplicate_computed_gotos_find_candidates (fun, candidates, max_size);
>
> +      bool changed = false;
> +      if (!bitmap_empty_p (candidates))
> +       changed = duplicate_computed_gotos_do_duplicate (fun, candidates);
>
> +      if (changed)
> +       fixup_partitions ();
> +
> +      cfg_layout_finalize ();

I don't think you have to go into/out-of cfglayout mode for each iteration.


>        /* Merge the duplicated blocks into predecessors, when possible.  */
> +      if (changed)
> +       cleanup_cfg (0);
> +      else
> +       break;
>      }

Maybe a gcc_assert that the loop doesn't iterate more often than num_edges?

Ciao!
Steven