> The following fixes a latent issue when we mark control edges but
> end up with marking a block with no stmts necessary. In this case
> we fail to mark dependent control edges of that block.
>
> Bootstrapped and tested on x86_64-unknown-linux-gnu.
>
> Does this look OK?
>
> Thanks,
> Richard.
>
> PR tree-optimization/106722
> * tree-ssa-dce.cc (mark_last_stmt_necessary): Return
> whether we marked a stmt.
> (mark_control_dependent_edges_necessary): When
> mark_last_stmt_necessary didn't mark any stmt make sure
> to mark its control dependent edges.
> (propagate_necessity): Likewise.
>
> * gcc.dg/torture/pr108737.c: New testcase.
> diff --git a/gcc/tree-ssa-dce.cc b/gcc/tree-ssa-dce.cc
> index b2fe9f4f55e..21b3294fc86 100644
> --- a/gcc/tree-ssa-dce.cc
> +++ b/gcc/tree-ssa-dce.cc
> @@ -327,17 +327,23 @@ mark_stmt_if_obviously_necessary (gimple *stmt, bool
> aggressive)
>
> /* Mark the last statement of BB as necessary. */
>
> -static void
> +static bool
> mark_last_stmt_necessary (basic_block bb)
> {
> gimple *stmt = last_stmt (bb);
>
> - bitmap_set_bit (last_stmt_necessary, bb->index);
> + if (!bitmap_set_bit (last_stmt_necessary, bb->index))
> + return true;
> +
> bitmap_set_bit (bb_contains_live_stmts, bb->index);
>
> /* We actually mark the statement only if it is a control statement. */
> if (stmt && is_ctrl_stmt (stmt))
> - mark_stmt_necessary (stmt, true);
> + {
> + mark_stmt_necessary (stmt, true);
> + return true;
> + }
> + return false;
> }
>
>
> @@ -369,8 +375,8 @@ mark_control_dependent_edges_necessary (basic_block bb,
> bool ignore_self)
> continue;
> }
>
> - if (!bitmap_bit_p (last_stmt_necessary, cd_bb->index))
> - mark_last_stmt_necessary (cd_bb);
> + if (!mark_last_stmt_necessary (cd_bb))
> + mark_control_dependent_edges_necessary (cd_bb, false);
Makes sense to me, though I am bit surprised it took such a long time to
show up.
Honza
