> Am 10.01.2026 um 06:34 schrieb Andrew Pinski <[email protected]>:
>
> So it turns out LOOPS_MAY_HAVE_MULTIPLE_LATCHES is set in places
> along compiling. Setting it only means there might be multiple
> latches currently. It does not mean let's go in an delete them
> all; which is what remove_forwarder_block does currently. This
> was happening before my set of patches too but since it was
> only happening in merge_phi pass, latches were not cleared away
> al of the time and then recreated.
>
> This solves the problem by protecting latches all of the time
> instead of depedent on LOOPS_MAY_HAVE_MULTIPLE_LATCHES not being set.
>
> vect-uncounted_7.c needs to be xfailed here because we no longer
> vectorize the code. Note the IR between GCC 15 and after this patch
> is the same so I think this was just a case were the testcase
> was added after the remove forwarder changes and should not have
> vectorized (or vectorize differently).
>
> Bootstrapped and tested on x86_64-linux-gnu.
Ok
Richard
> PR tree-optimization/123417
> gcc/ChangeLog:
>
> * tree-cfgcleanup.cc (maybe_remove_forwarder_block): Always
> protect latches.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.dg/vect/vect-uncounted_7.c: xfail vect test.
>
> Signed-off-by: Andrew Pinski <[email protected]>
> ---
> gcc/testsuite/gcc.dg/vect/vect-uncounted_7.c | 4 ++--
> gcc/tree-cfgcleanup.cc | 6 ++----
> 2 files changed, 4 insertions(+), 6 deletions(-)
>
> diff --git a/gcc/testsuite/gcc.dg/vect/vect-uncounted_7.c
> b/gcc/testsuite/gcc.dg/vect/vect-uncounted_7.c
> index 83aa3085ce7..d299c7fa433 100644
> --- a/gcc/testsuite/gcc.dg/vect/vect-uncounted_7.c
> +++ b/gcc/testsuite/gcc.dg/vect/vect-uncounted_7.c
> @@ -20,5 +20,5 @@ void foo(int i, char *p, char *q)
> }
> }
>
> -/* { dg-final { scan-tree-dump "Loop being analyzed as uncounted." "vect" }
> } */
> -/* { dg-final { scan-tree-dump "vectorized 1 loops in function" "vect" } } */
> +/* { dg-final { scan-tree-dump "Loop being analyzed as uncounted." "vect" }
> } */
> +/* { dg-final { scan-tree-dump "vectorized 1 loops in function" "vect" {
> xfail *-*-* } } } */
> diff --git a/gcc/tree-cfgcleanup.cc b/gcc/tree-cfgcleanup.cc
> index 929990cef2e..4cf754f5e56 100644
> --- a/gcc/tree-cfgcleanup.cc
> +++ b/gcc/tree-cfgcleanup.cc
> @@ -629,10 +629,8 @@ maybe_remove_forwarder_block (basic_block bb, bool
> can_split = false)
> return false;
> /* If bb doesn't have a single predecessor we'd make this
> loop have multiple latches. Don't do that if that
> - would in turn require disambiguating them. */
> - if (!single_pred_p (bb)
> - && !loops_state_satisfies_p
> - (LOOPS_MAY_HAVE_MULTIPLE_LATCHES))
> + would in turn require disambiguating them over again. */
> + if (!single_pred_p (bb))
> return false;
> }
> /* cleanup_tree_cfg_noloop just created the loop preheader, don't
> --
> 2.43.0
>
