> On Jun 30, 2021, at 1:59 PM, Richard Biener <rguent...@suse.de> wrote:
>
> On June 30, 2021 8:07:43 PM GMT+02:00, Qing Zhao <qing.z...@oracle.com> wrote:
>>
>>
>>> On Jun 30, 2021, at 12:36 PM, Richard Biener <rguent...@suse.de>
>> wrote:
>>>
>>> On June 30, 2021 7:20:18 PM GMT+02:00, Andrew Pinski
>> <pins...@gmail.com> wrote:
>>>> On Wed, Jun 30, 2021 at 8:47 AM Qing Zhao via Gcc-patches
>>>> <gcc-patches@gcc.gnu.org> wrote:
>>>>>
>>>>> I came up with a very simple testing case that can repeat the same
>>>> issue:
>>>>>
>>>>> [qinzhao@localhost gcc]$ cat t.c
>>>>> extern void bar (int);
>>>>> void foo (int a)
>>>>> {
>>>>> int i;
>>>>> for (i = 0; i < a; i++) {
>>>>> if (__extension__({int size2;
>>>>> size2 = 4;
>>>>> size2 > 5;}))
>>>>> bar (a);
>>>>> }
>>>>> }
>>>>
>>>> You should show the full dump,
>>>> What we have is the following:
>>>>
>>>>
>>>>
>>>> size2_3 = PHI <size2_1(D), size2_13>
>>>> <bb 3> :
>>>>
>>>> size2_12 = .DEFERRED_INIT (size2_3, 2);
>>>> size2_13 = 4;
>>>>
>>>> So CCP decides to propagate 4 into the PHI and then decides
>> size2_1(D)
>>>> is undefined so size2_3 is then considered 4 and propagates it into
>>>> the .DEFERRED_INIT.
>>>
>>> Which means the DEFERED_INIT is inserted at the wrong place.
>>
>> Then, where is the correct place for “.DEFERRED_INIT(size2,2)?
>>
>> The variable “size2” is a block scope variable which is declared inside
>> the “if” condition:
>
> But that's obviously not how it behaves
> During into SSA phase since we're inserting a PHI for it - and we're
> inserting it because of the use in the DEFERED_INIT call. I suppose you need
> to fiddle with the SSA rewrite and avoid treating the use as a use but only
> for the purpose of inserting PHIs...
>
> You might be able to construct a testcase which has a use before the real
> init where then the optimistic CCP propagation will defeat the DEFERED_INIT
> otherwise.
>
> I'd need to play with the actual patch to find a good solution to this
> problem.
Do you want me send you the current patch (4th version) with email?
Or I have a branch at
https://gitlab.com/x86-gcc/gcc.git
users/qinzhao/auto-init/v3
(And I am currently try to change the DEFERRED_INIT call from:
temp = .DEFERRED_INIT (temp/WITH_SIZE_EXPR(temp), init_type)
To:
temp = .DEFERRED_INIT (SIZE_of_temp, init_type)
And this solution successfully hide this CCP issue and also simplify the
implementation at the same time.)
Qing
>
> Richard.
>
>>>>> if (__extension__({int size2;
>>>>> size2 = 4;
>>>>> size2 > 5;}))
>>
>> So, it’s reasonable to insert the initialization inside this block and
>> immediately after the declaration, This is what the patch currently
>> does:
>>
>> *****The full dump of “gimple” phase is:
>>
>> void foo (int a)
>> {
>> int D.2240;
>> int i;
>>
>> i = .DEFERRED_INIT (i, 2);
>> i = 0;
>> goto <D.2244>;
>> <D.2243>:
>> {
>> int size2;
>>
>> size2 = .DEFERRED_INIT (size2, 2);
>> size2 = 4;
>> _1 = size2 > 5;
>> D.2240 = (int) _1;
>> }
>> if (D.2240 != 0) goto <D.2246>; else goto <D.2247>;
>> <D.2246>:
>> bar (a);
>> <D.2247>:
>> i = i + 1;
>> <D.2244>:
>> if (i < a) goto <D.2243>; else goto <D.2241>;
>> <D.2241>:
>> }
>>
>> However, I suspect that the SSA phase moved the “size2” out of its
>> block scope as following:
>>
>> ******The full “SSA” dump is:
>>
>> ;; Function foo (foo, funcdef_no=0, decl_uid=2236, cgraph_uid=1,
>> symbol_order=0)
>>
>> void foo (int a)
>> {
>> int size2;
>> int i;
>> _Bool _1;
>> int _14;
>>
>> <bb 2> :
>> i_7 = .DEFERRED_INIT (i_6(D), 2);
>> i_8 = 0;
>> goto <bb 6>; [INV]
>>
>> <bb 3> :
>> size2_12 = .DEFERRED_INIT (size2_3, 2);
>> size2_13 = 4;
>> _1 = size2_13 > 5;
>> _14 = (int) _1;
>> if (_14 != 0)
>> goto <bb 4>; [INV]
>> else
>> goto <bb 5>; [INV]
>>
>> <bb 4> :
>> bar (a_11(D));
>>
>> <bb 5> :
>> i_16 = i_2 + 1;
>>
>> <bb 6> :
>> # i_2 = PHI <i_8(2), i_16(5)>
>> # size2_3 = PHI <size2_9(D)(2), size2_13(5)>
>> if (i_2 < a_11(D))
>> goto <bb 3>; [INV]
>> else
>> goto <bb 7>; [INV]
>>
>> <bb 7> :
>> return;
>>
>> }
>>
>> In the above, we can see that “ # size2_3 = PHI <size2_9(D)(2),
>> size2_13(5)>” is outside of its block scope already.
>> “size2” should not be in the same scope as “I" .
>>
>> This looks incorrect SSA transformation to me.
>>
>> What do you think?
>>
>> Qing
>>
>>>
>>> Richard.
>>>>
>>>> Thanks,
>>>> Andrew
>>>>
>>>>
>>>>>
>>>>> [qinzhao@localhost gcc]$
>>>> /home/qinzhao/Work/GCC/gcc_build_debug/gcc/xgcc
>>>> -B/home/qinzhao/Work/GCC/gcc_build_debug/gcc/ -std=c99 -m64
>>>> -march=native -ftrivial-auto-var-init=zero t.c -fdump-tree-all -O1
>>>>> t.c: In function ‘foo’:
>>>>> t.c:11:1: error: ‘DEFFERED_INIT’ calls should have the same LHS as
>>>> the first argument
>>>>> 11 | }
>>>>> | ^
>>>>> size2_12 = .DEFERRED_INIT (4, 2);
>>>>> during GIMPLE pass: ccp
>>>>> dump file: a-t.c.032t.ccp1
>>>>> t.c:11:1: internal compiler error: verify_gimple failed
>>>>> 0x143ee47 verify_gimple_in_cfg(function*, bool)
>>>>> ../../latest_gcc/gcc/tree-cfg.c:5501
>>>>> 0x122d799 execute_function_todo
>>>>> ../../latest_gcc/gcc/passes.c:2042
>>>>> 0x122c74b do_per_function
>>>>> ../../latest_gcc/gcc/passes.c:1687
>>>>> 0x122d986 execute_todo
>>>>> ../../latest_gcc/gcc/passes.c:2096
>>>>> Please submit a full bug report,
>>>>> with preprocessed source if appropriate.
>>>>> Please include the complete backtrace with any bug report.
>>>>> See <https://gcc.gnu.org/bugs/> for instructions.
>>>>>
>>>>> In this testing case, both “I” and “size2” are auto vars that are
>> not
>>>> initialized at declaration but are initialized later by assignment.
>>>>> However, “I” doesn’t have any issue, but “size2” has such issue.
>>>>>
>>>>> ******“ssa” dump:
>>>>>
>>>>> <bb 2> :
>>>>> i_7 = .DEFERRED_INIT (i_6(D), 2);
>>>>> i_8 = 0;
>>>>> goto <bb 6>; [INV]
>>>>>
>>>>> <bb 3> :
>>>>> size2_12 = .DEFERRED_INIT (size2_3, 2);
>>>>> size2_13 = 4;
>>>>>
>>>>> ******”ccp1” dump:
>>>>>
>>>>> <bb 2> :
>>>>> i_7 = .DEFERRED_INIT (i_6(D), 2);
>>>>> goto <bb 4>; [INV]
>>>>>
>>>>> <bb 3> :
>>>>> size2_12 = .DEFERRED_INIT (4, 2);
>>>>>
>>>>> So, I am wondering: Is it possible that “ssa” phase have a bug ?
>>>>>
>>>>> Qing
>>>>>
>>>>>> On Jun 30, 2021, at 9:39 AM, Richard Biener <rguent...@suse.de>
>>>> wrote:
>>>>>>
>>>>>> On Wed, 30 Jun 2021, Qing Zhao wrote:
>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> On Jun 30, 2021, at 2:46 AM, Richard Biener
>>>> <rguent...@suse.de<mailto:rguent...@suse.de>> wrote:
>>>>>>>
>>>>>>> On Wed, 30 Jun 2021, Qing Zhao wrote:
>>>>>>>
>>>>>>> Hi,
>>>>>>>
>>>>>>> I am testing the 4th patch of -ftrivial-auto-var-init with
>> CPU2017
>>>> today, and found the following issues:
>>>>>>>
>>>>>>> ****In the dump file of “*t.i.031t.objsz1”, we have:
>>>>>>>
>>>>>>> <bb 3> :
>>>>>>> __s1_len_217 = .DEFERRED_INIT (__s1_len_176, 2);
>>>>>>> __s2_len_218 = .DEFERRED_INIT (__s2_len_177, 2);
>>>>>>>
>>>>>>> I looks like this .DEFERRED_INIT initializes an already
>>>> initialized
>>>>>>> variable.
>>>>>>>
>>>>>>> Yes.
>>>>>>>
>>>>>>> For cases like the following:
>>>>>>>
>>>>>>> int s2_len;
>>>>>>> s2_len = 4;
>>>>>>>
>>>>>>> i.e, the initialization is not at the declaration.
>>>>>>>
>>>>>>> We cannot avoid initialization for such cases.
>>>>>>
>>>>>> But I'd have expected
>>>>>>
>>>>>> s2_len = .DEFERRED_INIT (s2_len, 0);
>>>>>> s2_len = 4;
>>>>>>
>>>>>> from the above - thus the deferred init _before_ the first
>>>>>> "use" which is the explicit init. How does the other order
>>>>>> happen to materialize? As said, I believe it shouldn't.
>>>>>>
>>>>>>> I'd expect to only ever see default definition SSA names
>>>>>>> as first argument to .DEFERRED_INIT.
>>>>>>>
>>>>>>> You mean something like:
>>>>>>> __s2_len_218 = .DEFERRED_INIT (__s2_len, 2);
>>>>>>
>>>>>> No,
>>>>>>
>>>>>> __s2_len_218 = .DEFERRED_INIT (__s2_len_217(D), 2);
>>>>>>
>>>>>>> ?
>>>>>>>
>>>>>>>
>>>>>>> __s2_len_219 = 7;
>>>>>>> if (__s2_len_219 <= 3)
>>>>>>> goto <bb 4>; [INV]
>>>>>>> else
>>>>>>> goto <bb 9>; [INV]
>>>>>>>
>>>>>>> <bb 4> :
>>>>>>> _1 = (long unsigned int) i_175;
>>>>>>>
>>>>>>>
>>>>>>> ****However, after “ccp”, in “t.i.032t.ccp1”, we have:
>>>>>>>
>>>>>>> <bb 3> :
>>>>>>> __s1_len_217 = .DEFERRED_INIT (__s1_len_176, 2);
>>>>>>> __s2_len_218 = .DEFERRED_INIT (7, 2);
>>>>>>> _36 = (long unsigned int) i_175;
>>>>>>> _37 = _36 * 8;
>>>>>>> _38 = argv_220(D) + _37;
>>>>>>>
>>>>>>>
>>>>>>> Looks like that the optimization “ccp” replaced the first
>> argument
>>>> of the call .DEFERRED_INIT with the constant 7.
>>>>>>> This should be avoided.
>>>>>>>
>>>>>>> (NOTE, this issue existed in the previous patches, however, only
>>>> exposed with this version since I added more verification
>>>>>>> code in tree-cfg.c to verify the call to .DEFERRED_INIT).
>>>>>>>
>>>>>>> I am wondering what’s the best solution to this problem?
>>>>>>>
>>>>>>> I think you have to trace where this "bogus" .DEFERRED_INIT comes
>>>> from
>>>>>>> originally. Or alternatively, if this is unavoidable,
>>>>>>>
>>>>>>> This is unavoidable, I believe.
>>>>>>
>>>>>> I see but don't believe it yet ;)
>>>>>>
>>>>>>> add "constant
>>>>>>> folding" of .DEFERRED_INIT so that defered init of an initialized
>>>>>>> object becomes the object itself, thus retain the previous -
>>>> eventually
>>>>>>> partial - initialization only.
>>>>>>>
>>>>>>> If this additional .DEFERRED_INIT will be kept till RTL expansion
>>>> phase, then it will become a real initialization:
>>>>>>>
>>>>>>> i.e.
>>>>>>>
>>>>>>> s2_len = 0; //.DEFERRED_INIT expanded
>>>>>>> s2_len = 4; // the original initialization
>>>>>>>
>>>>>>> Then the first initialization will be eliminated by current RTL
>>>> optimization easily, right?
>>>>>>
>>>>>> Well, in your example above it's effectively elimiated by GIMPLE
>>>>>> optimization. IIRC you're using the first argument of
>>>> .DEFERRED_INIT
>>>>>> for diagnostic purposes only, correct?
>>>>>>
>>>>>> Richard.
>>>>>>
>>>>>>> Qing
>>>>>>>
>>>>>>>
>>>>>>> Richard.
>>>>>>>
>>>>>>> Can we add any attribute to the internal function argument to
>>>> prevent later optimizations that might applied on it?
>>>>>>> Or just update “ccp” phase to specially handle calls to
>>>> .DEFERRED_INIT? (Not sure whether there are other phases have the
>>>>>>> Same issue?)
>>>>>>>
>>>>>>> Let me know if you have any suggestion.
>>>>>>>
>>>>>>> Thanks a lot for your help.
>>>>>>>
>>>>>>> Qing
>>>>>>>
>>>>>>> --
>>>>>>> Richard Biener <rguent...@suse.de<mailto:rguent...@suse.de>>
>>>>>>> SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409
>>>> Nuernberg,
>>>>>>> Germany; GF: Felix Imendörffer; HRB 36809 (AG Nuernberg)
>>>>>>>
>>>>>>>
>>>>>>
>>>>>> --
>>>>>> Richard Biener <rguent...@suse.de>
>>>>>> SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409
>>>> Nuernberg,
>>>>>> Germany; GF: Felix Imendörffer; HRB 36809 (AG Nuernberg)
>>>>>
>>>
>
