On Fri, Jan 14, 2022 at 7:21 PM Alexander Monakov <amona...@ispras.ru> wrote:
>
> A returns_twice call may have associated abnormal edges that correspond
> to the "second return" from the call. If the call is duplicated, the
> copies of those edges also need to be abnormal, but e.g. tracer does not
> enforce that. Just prohibit the (unlikely to be useful) duplication.
The general CFG copying routines properly duplicate those edges, no?
Tracer uses duplicate_block so it should also get copies of all successor
edges of that block. It also only traces along normal edges. What it might
miss is abnormal incoming edges - is that what you are referring to?
That would be a thing we don't handle in duplicate_block on its own but
that callers are expected to do (though I don't see copy_bbs doing that
either). I wonder if we can trigger this issue for some testcase?
The thing to check would be incoming abnormal edges in
can_duplicate_block_p, not (only) returns twice functions?
Richard.
> gcc/ChangeLog:
>
> * tree-cfg.c (gimple_can_duplicate_bb_p): Reject blocks with
> calls that may return twice.
> ---
> gcc/tree-cfg.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/gcc/tree-cfg.c b/gcc/tree-cfg.c
> index b7fe313b7..a99f1acb4 100644
> --- a/gcc/tree-cfg.c
> +++ b/gcc/tree-cfg.c
> @@ -6304,12 +6304,15 @@ gimple_can_duplicate_bb_p (const_basic_block bb)
> {
> gimple *g = gsi_stmt (gsi);
>
> - /* An IFN_GOMP_SIMT_ENTER_ALLOC/IFN_GOMP_SIMT_EXIT call must be
> + /* Prohibit duplication of returns_twice calls, otherwise associated
> + abnormal edges also need to be duplicated properly.
> + An IFN_GOMP_SIMT_ENTER_ALLOC/IFN_GOMP_SIMT_EXIT call must be
> duplicated as part of its group, or not at all.
> The IFN_GOMP_SIMT_VOTE_ANY and IFN_GOMP_SIMT_XCHG_* are part of such
> a
> group, so the same holds there. */
> if (is_gimple_call (g)
> - && (gimple_call_internal_p (g, IFN_GOMP_SIMT_ENTER_ALLOC)
> + && (gimple_call_flags (g) & ECF_RETURNS_TWICE
> + || gimple_call_internal_p (g, IFN_GOMP_SIMT_ENTER_ALLOC)
> || gimple_call_internal_p (g, IFN_GOMP_SIMT_EXIT)
> || gimple_call_internal_p (g, IFN_GOMP_SIMT_VOTE_ANY)
> || gimple_call_internal_p (g, IFN_GOMP_SIMT_XCHG_BFLY)
> --
> 2.33.1
>
