https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81192
--- Comment #5 from Tom de Vries <vries at gcc dot gnu.org> ---
There actually is some code in find_same_succ_bb to keep loop structure:
...
if (bb == NULL
/* Be conservative with loop structure. It's not evident that this test
is sufficient. Before tail-merge, we've just called
loop_optimizer_finalize, and LOOPS_MAY_HAVE_MULTIPLE_LATCHES is now
set, so there's no guarantee that the loop->latch value is still
valid.
But we assume that, since we've forced LOOPS_HAVE_SIMPLE_LATCHES at
the
start of pre, we've kept that property intact throughout pre, and are
keeping it throughout tail-merge using this test. */
|| bb->loop_father->latch == bb)
return;
...
For this example, the cleanup_tree_cfg in tail_merge_optimize creates multiple
loop latches in the inner loop, so the loop->latch value is no longer valid.
This test needs fixing.
