Re: [PATCH] Pass manager: add support for termination of pass list

[Richard Biener <richard.guenther@gmail.com>]

On Thu, Oct 22, 2015 at 1:02 PM, Martin Liška <mliska@suse.cz> wrote:
> On 10/21/2015 04:06 PM, Richard Biener wrote:
>> On Wed, Oct 21, 2015 at 1:24 PM, Martin Liška <mliska@suse.cz> wrote:
>>> On 10/21/2015 11:59 AM, Richard Biener wrote:
>>>> On Wed, Oct 21, 2015 at 11:19 AM, Martin Liška <mliska@suse.cz> wrote:
>>>>> On 10/20/2015 03:39 PM, Richard Biener wrote:
>>>>>> On Tue, Oct 20, 2015 at 3:00 PM, Martin Liška <mliska@suse.cz> wrote:
>>>>>>> Hello.
>>>>>>>
>>>>>>> As part of upcoming merge of HSA branch, we would like to have possibility to terminate
>>>>>>> pass manager after execution of the HSA generation pass. The HSA back-end is implemented
>>>>>>> as a tree pass that directly emits HSAIL from gimple tree representation. The pass operates
>>>>>>> on clones created by HSA IPA pass and the pass manager should stop execution of further
>>>>>>> RTL passes.
>>>>>>>
>>>>>>> Suggested patch survives bootstrap and regression tests on x86_64-linux-pc.
>>>>>>>
>>>>>>> What do you think about it?
>>>>>>
>>>>>> Are you sure it works this way?
>>>>>>
>>>>>> Btw, you will miss executing of all the cleanup passes that will
>>>>>> eventually free memory
>>>>>> associated with the function.  So I'd rather support a
>>>>>> TODO_discard_function which
>>>>>> should basically release the body from the cgraph.
>>>>>
>>>>> Hi.
>>>>>
>>>>> Agree with you that I should execute all TODOs, which can be easily done.
>>>>> However, if I just try to introduce the suggested TODO and handle it properly
>>>>> by calling cgraph_node::release_body, then for instance fn->gimple_df, fn->cfg are
>>>>> released and I hit ICEs on many places.
>>>>>
>>>>> Stopping the pass manager looks necessary, or do I miss something?
>>>>
>>>> "Stopping the pass manager" is necessary after TODO_discard_function, yes.
>>>> But that may be simply done via a has_body () check then?
>>>
>>> Thanks, there's second version of the patch. I'm going to start regression tests.
>>
>> As release_body () will free cfun you should pop_cfun () before
>> calling it (and thus
>
> Well, release_function_body calls both push & pop, so I think calling pop
> before cgraph_node::release_body is not necessary.

(ugh).

> If tried to call pop_cfun before cgraph_node::release_body, I have cfun still
> pointing to the same (function *) (which is gcc_freed, but cfun != NULL).

Hmm, I meant to call pop_cfun then after it (unless you want to fix the above,
none of the freeing functions should techincally need 'cfun', just add
'fn' parameters ...).

I expected pop_cfun to eventually set cfun to NULL if it popped the
"last" cfun.  Why
doesn't it do that?

>> drop its modification).  Also TODO_discard_functiuon should be only set for
>> local passes thus you should probably add a gcc_assert (cfun).
>> I'd move its handling earlier, definitely before the ggc_collect, eventually
>> before the pass_fini_dump_file () (do we want a last dump of the
>> function or not?).
>
> Fully agree, moved here.
>
>>
>> @@ -2397,6 +2410,10 @@ execute_pass_list_1 (opt_pass *pass)
>>      {
>>        gcc_assert (pass->type == GIMPLE_PASS
>>                   || pass->type == RTL_PASS);
>> +
>> +
>> +      if (!gimple_has_body_p (current_function_decl))
>> +       return;
>>
>> too much vertical space.  With popping cfun before releasing the body the check
>> might just become if (!cfun) and
>
> As mentioned above, as release body is symmetric (calling push & pop), the suggested
> guard will not work.

I suggest to fix it.  If it calls push/pop it should leave with the
original cfun, popping again
should make it NULL?

>>
>> @@ -2409,7 +2426,7 @@ execute_pass_list (function *fn, opt_pass *pass)
>>  {
>>    push_cfun (fn);
>>    execute_pass_list_1 (pass);
>> -  if (fn->cfg)
>> +  if (gimple_has_body_p (current_function_decl) && fn->cfg)
>>      {
>>        free_dominance_info (CDI_DOMINATORS);
>>        free_dominance_info (CDI_POST_DOMINATORS);
>>
>> here you'd need to guard the pop_cfun call on cfun != NULL.  IMHO it's better
>> to not let cfun point to deallocated data.
>
> As I've read the code, since we gcc_free 'struct function', one can just rely on
> gimple_has_body_p (current_function_decl) as it correctly realizes that
> DECL_STRUCT_FUNCTION (current_function_decl) == NULL.

I'm sure that with some GC checking ggc_free makes them #deadbeef or so:

void
ggc_free (void *p)
{
...
#ifdef ENABLE_GC_CHECKING
  /* Poison the data, to indicate the data is garbage.  */
  VALGRIND_DISCARD (VALGRIND_MAKE_MEM_UNDEFINED (p, size));
  memset (p, 0xa5, size);
#endif

so I don't think that's a good thing to rely on ;)

Richard.

> I'm attaching v3.
>
> Thanks,
> Martin
>
>>
>> Otherwise looks good to me.
>>
>> Richard.
>>
>>
>>> Martin
>>>
>>>>
>>>>> Thanks,
>>>>> Martin
>>>>>
>>>>>>
>>>>>> Richard.
>>>>>>
>>>>>>> Thanks,
>>>>>>> Martin
>>>>>
>>>
>