Re: [PATCH 6/21]middle-end: support multiple exits in loop versioning

[Richard Biener]

On Mon, 6 Nov 2023, Tamar Christina wrote:

> Hi All,
> 
> This has loop versioning use the vectorizer's IV exit edge when it's available
> since single_exit (..) fails with multiple exits.
> 
> Bootstrapped Regtested on aarch64-none-linux-gnu and no issues.
> 
> Ok for master?
> 
> Thanks,
> Tamar
> 
> gcc/ChangeLog:
> 
>       * tree-vect-loop-manip.cc (vect_loop_versioning): Support multiple
>       exits.
> 
> --- inline copy of patch -- 
> diff --git a/gcc/tree-vect-loop-manip.cc b/gcc/tree-vect-loop-manip.cc
> index 
> 3d59119787d6afdc5a6465a547d1ea2d3d940373..58b4b9c11d8b844ee86156cdfcba7f838030a7c2
>  100644
> --- a/gcc/tree-vect-loop-manip.cc
> +++ b/gcc/tree-vect-loop-manip.cc
> @@ -4180,12 +4180,24 @@ vect_loop_versioning (loop_vec_info loop_vinfo,
>        If loop versioning wasn't done from loop, but scalar_loop instead,
>        merge_bb will have already just a single successor.  */
>  
> -      merge_bb = single_exit (loop_to_version)->dest;
> +      /* Due to the single_exit check above we should only get here when
> +      loop == loop_to_version, that means we can use loop_vinfo to get the
> +      exits.  */

You mean LOOP_VINFO_EARLY_BREAKS can only ever version the loop
itself?  That's correct.  All inner loops of loop_to_version have
a single exit unless it's loop itself.

Please reword a bit and instead do

       edge exit_edge;
       if (loop_to_version == loop)
         exit_edge = LOOP_VINFO_IV_EXIT (loop_vinfo);
       else
         exit_edge = single_exit (loop_to_version);

OK with that change.

Richard.

> +      edge exit_edge = single_exit (loop_to_version);
> +      if (LOOP_VINFO_EARLY_BREAKS (loop_vinfo))
> +     {
> +       /* In early exits the main exit will fail into the merge block of the
> +          alternative exits.  So we need the single successor of the main
> +          exit here to find the merge block.  */
> +       exit_edge = LOOP_VINFO_IV_EXIT (loop_vinfo);
> +     }
> +      gcc_assert (exit_edge);
> +      merge_bb = exit_edge->dest;
>        if (EDGE_COUNT (merge_bb->preds) >= 2)
>       {
>         gcc_assert (EDGE_COUNT (merge_bb->preds) >= 2);
> -       new_exit_bb = split_edge (single_exit (loop_to_version));
> -       new_exit_e = single_exit (loop_to_version);
> +       new_exit_bb = split_edge (exit_edge);
> +       new_exit_e = exit_edge;
>         e = EDGE_SUCC (new_exit_bb, 0);
>  
>         for (gsi = gsi_start_phis (merge_bb); !gsi_end_p (gsi);