Re: [PATCH 3/3] tree-cfg: check placement of returns_twice calls

[Richard Biener <richard.guenther@gmail.com>]

On Fri, Jan 14, 2022 at 7:21 PM Alexander Monakov <amonakov@ispras.ru> wrote:
>
> When a returns_twice call has an associated abnormal edge, the edge
> corresponds to the "second return" from the call. It wouldn't make sense
> if any executable statements appeared between the call and the
> destination of the edge (they wouldn't be re-executed upon the "second
> return"), so verify that.

OK for next stage1.

Thanks,
Richard.

> gcc/ChangeLog:
>
>         * tree-cfg.c (gimple_verify_flow_info): Check placement of
>         returns_twice calls.
> ---
>  gcc/tree-cfg.c | 33 +++++++++++++++++++++++++++++++++
>  1 file changed, 33 insertions(+)
>
> diff --git a/gcc/tree-cfg.c b/gcc/tree-cfg.c
> index a99f1acb4..70bd31d3d 100644
> --- a/gcc/tree-cfg.c
> +++ b/gcc/tree-cfg.c
> @@ -5644,6 +5644,7 @@ gimple_verify_flow_info (void)
>         }
>
>        /* Verify that body of basic block BB is free of control flow.  */
> +      bool seen_nondebug_stmt = false;
>        for (; !gsi_end_p (gsi); gsi_next (&gsi))
>         {
>           gimple *stmt = gsi_stmt (gsi);
> @@ -5664,6 +5665,38 @@ gimple_verify_flow_info (void)
>                      gimple_label_label (label_stmt), bb->index);
>               err = 1;
>             }
> +
> +         /* Check that no statements appear between a returns_twice call
> +            and its associated abnormal edge.  */
> +         if (gimple_code (stmt) == GIMPLE_CALL
> +             && gimple_call_flags (stmt) & ECF_RETURNS_TWICE)
> +           {
> +             const char *misplaced = NULL;
> +             /* TM is an exception: it points abnormal edges just after the
> +                call that starts a transaction, i.e. it must end the BB.  */
> +             if (gimple_call_builtin_p (stmt, BUILT_IN_TM_START))
> +               {
> +                 if (single_succ_p (bb)
> +                     && bb_has_abnormal_pred (single_succ (bb))
> +                     && !gsi_one_nondebug_before_end_p (gsi))
> +                   misplaced = "not last";
> +               }
> +             else
> +               {
> +                 if (seen_nondebug_stmt
> +                     && bb_has_abnormal_pred (bb))
> +                   misplaced = "not first";
> +               }
> +             if (misplaced)
> +               {
> +                 error ("returns_twice call is %s in basic block %d",
> +                        misplaced, bb->index);
> +                 print_gimple_stmt (stderr, stmt, 0, TDF_SLIM);
> +                 err = 1;
> +               }
> +           }
> +         if (!is_gimple_debug (stmt))
> +           seen_nondebug_stmt = true;
>         }
>
>        gsi = gsi_last_nondebug_bb (bb);
> --
> 2.33.1
>