> Am 12.11.2019 um 15:32 schrieb Segher Boessenkool
> <seg...@kernel.crashing.org>:
>
> Hi!
>
> On Tue, Nov 12, 2019 at 03:11:05PM +0100, Ilya Leoshkevich wrote:
>> try_forward_edges does not update dominance info, and merge_blocks
>> relies on it being up-to-date. In PR92430 stale dominance info makes
>> merge_blocks produce a loop in the dominator tree, which in turn makes
>> delete_basic_block loop forever.
>>
>> Fix by freeing dominance info at the beginning of cleanup_cfg.
>
>> --- a/gcc/cfgcleanup.c
>> +++ b/gcc/cfgcleanup.c
>> @@ -3312,6 +3312,9 @@ public:
>> unsigned int
>> pass_jump_after_combine::execute (function *)
>> {
>> + /* Jump threading does not keep dominators up-to-date. */
>> + free_dominance_info (CDI_DOMINATORS);
>> + free_dominance_info (CDI_POST_DOMINATORS);
>> cleanup_cfg (flag_thread_jumps ? CLEANUP_THREADING : 0);
>> return 0;
>> }
>
> Why do you always free it, if if only gets invalidated if flag_thread_jumps?
>
> It may be a good idea to throw away the dom info anyway, but the comment
> seems off then?
Hmm, come to think of it, it would make sense to make flag_thread_jumps
a gate for this pass, and then run free_dominance_info (CDI_DOMINATORS)
and cleanup_cfg (CLEANUP_THREADING) unconditionally. What do you think?
Best regards,
Ilya
