[llvm-commits] [LLVM, PR11652 PATCH]: Fixed Bug 11652 - assertion failures when Type.cpp is compiled with -Os
Stepan Dyatkovskiy
STPWORLD at narod.ru
Tue Jan 3 10:50:21 PST 2012
Hi, Duncan. Please find the second patch attached.
-Stepan.
03.01.2012, 18:21, "Duncan Sands" <baldrick at free.fr>:
> Hi Stepan,
>
>> Oh.. of course. Commited as r147446. For next patch, did you mean that I should check that TypeID was properly stored in its 8 bits? Something like this:
>>
>> void setTypeID(TypeID ID) {
>> IDAndSubclassData = (ID& 0xFF) | (IDAndSubclassData& 0xFFFFFF00);
>> assert(IDAndSubclassData& 0xFF == ID&& "Type data too large for field");
>> }
>
> yes, something like that. Better to use
>
> assert(getTypeID() == ID && "Type data too large for field!");
>
> though IMO.
>
> Ciao, Duncan.
>
>> -Stepan
>>
>> 03.01.2012, 12:51, "Duncan Sands"<baldrick at free.fr>:
>>> Hi Stepan,
>>>> Hi Duncan, can I use DataTypes.h instead?
>>> this patch doesn't require either. It is the next patch that needs it, right?
>>>
>>> Ciao, Duncan.
>>>> -Stepan.
>>>>
>>>> 03.01.2012, 12:32, "Duncan Sands"<baldrick at free.fr>:
>>>>> Hi Stepan, this looks fine except for a pointless include of stdint.h. Please
>>>>> apply, except for the include.
>>>>>
>>>>> Thanks for doing this,
>>>>>
>>>>> Duncan.
>>>>>> Hi, Duncan. Please find the first patch in attachment. Replacement: ID with getTypeID().
>>>>>> - Stepan
>>>>>>
>>>>>> 02.01.2012, 19:25, "Duncan Sands"<baldrick at free.fr>:
>>>>>>> Hi Stepan,
>>>>>>>> OK. Please look at patch in attachment.
>>>>>>>> I'm not sure that it is better than previous patch. Probably the first one looks like a workaround, but it changes setSubclassData only. New patch changes set/getSubclassData set/getTypeID, and all methods that uses ID.
>>>>>>> thanks for doing this. I think it is a better abstraction to have getters
>>>>>>> and setters for ID, like the ones that already exist for SubclassData. Can
>>>>>>> you therefore split the patch in two: one patch that adds getters and setters,
>>>>>>> and then a second one that drops the bitfield in favour of explicit bit
>>>>>>> fiddling.
>>>>>>>
>>>>>>> Additional comments:
>>>>>>> - you made some lines too long (> 80 columns).
>>>>>>> - this is not your fault, but I think there should be a check that ID values
>>>>>>> fit in the allocated space, for example by checking somehow that there is
>>>>>>> enough room for every value of the TypeID type. Alternatively, in setTypeID
>>>>>>> check that the value you read back out matches the value put in. The
>>>>>>> constructor can also set the ID. It should probably initialize
>>>>>>> IDAndSubclassData to zero, and then call setTypeID in the body of the
>>>>>>> constructor to set the value.
>>>>>>>
>>>>>>> Ciao, Duncan.
>>>>>>>> -Stepan.
>>>>>>>>
>>>>>>>> 02.01.2012, 15:04, "Duncan Sands"<baldrick at free.fr>:
>>>>>>>>> Hi Stepan,
>>>>>>>>>> ID is used very extensively in Type.h. We need to fix a lots, so we need to fix all methods like:
>>>>>>>>>> bool isIntegerTy() const { return ID == IntegerTyID; }
>>>>>>>>> you could turn ID into a private method that extracts the id part of the field.
>>>>>>>>> Then you just need to turn ID into ID() in places such as isIntegerTy. Likewise
>>>>>>>>> for SubclassData.
>>>>>>>>>> But in the same time we can apply some working decision until gcc bug will fixed.
>>>>>>>>>> May be add some dummy field?
>>>>>>>>>> TypeID ID : 8;
>>>>>>>>>> unsigned SubclassData : 24;
>>>>>>>>>> unsigned KungFuPanda; // Will protect NumContainedTys from overwriting.
>>>>>>>>>> unsigned NumContainedTys; // Will OK.
>>>>>>>>> Even if the gcc bug is fixed, people will be using older compilers with the bug
>>>>>>>>> for years to come. So this field would be around essentially forever. Given
>>>>>>>>> that, I don't think this is a good solution. If you are prepared to make the
>>>>>>>>> class bigger, you might as well not have the fields be bitfields at all (and
>>>>>>>>> change the order so that things are well packed).
>>>>>>>>>
>>>>>>>>> Ciao, Duncan.
>>>>>>>>>> -Stepan.
>>>>>>>>>>
>>>>>>>>>> 02.01.2012, 14:38, "Duncan Sands"<baldrick at free.fr>:
>>>>>>>>>>> Hi Stepan,
>>>>>>>>>>>> I tried it doesn't helps. Now it seems that ID is overwritten. 4807 unexpected failures.
>>>>>>>>>>> OK, thanks for the info. How about doing the bit fiddling yourself instead?
>>>>>>>>>>> I.e. rather than trying to fool the optimizers, don't use bitfields: declare
>>>>>>>>>>> an unsigned field IDAndSubclassData and store and load values from it using
>>>>>>>>>>> explicit shifts etc. This would then completely avoid all problems coming
>>>>>>>>>>> from misoptimization of bitfields (which has happened a lot historically),
>>>>>>>>>>> and would be less fragile than trying to fool the optimizers via some magic
>>>>>>>>>>> incantation.
>>>>>>>>>>>
>>>>>>>>>>> Ciao, Duncan.
>>>>>>>>>>>> -Stepan.
>>>>>>>>>>>>
>>>>>>>>>>>> 02.01.2012, 14:02, "Duncan Sands"<baldrick at free.fr>:
>>>>>>>>>>>>> Hi Stepan,
>>>>>>>>>>>>>> The problem is in Type.h. The fields in Type class are declared in next order:
>>>>>>>>>>>>>> TypeID ID : 8;
>>>>>>>>>>>>>> unsigned SubclassData : 24;
>>>>>>>>>>>>>> unsigned NumContainedTys;
>>>>>>>>>>>>> does the problem still occur if you flip the order of ID and SubclassData?
>>>>>>>>>>>>> I.e.
>>>>>>>>>>>>> unsigned SubclassData : 24;
>>>>>>>>>>>>> TypeID ID : 8;
>>>>>>>>>>>>> unsigned NumContainedTys;
>>>>>>>>>>>>> ?
>>>>>>>>>>>>> Ciao, Duncan.
>>>>>>>>>>>>>> Attempt to set new SubclassData value rewrites lowest byte in NumContainedTys
>>>>>>>>>>>>>> when -Os is set. GCC bug? Anyway setting SubclassData with two workaround
>>>>>>>>>>>>>> strings fixes the problem:
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> void setSubclassData(unsigned val) {
>>>>>>>>>>>>>> unsigned tmp = NumContainedTys; // Workaround for GCC -Os
>>>>>>>>>>>>>> SubclassData = val;
>>>>>>>>>>>>>> NumContainedTys = tmp; // Workaround for GCC -Os
>>>>>>>>>>>>>> // Ensure we don't have any accidental truncation.
>>>>>>>>>>>>>> assert(SubclassData == val&& "Subclass data too large for field");
>>>>>>>>>>>>>> }
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> Probably there is another ways to protect NumContainedTys from overwritting?
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> Please find the patch in attachment for review.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> -Stepan.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> _______________________________________________
>>>>>>>>>>>>>> llvm-commits mailing list
>>>>>>>>>>>>>> llvm-commits at cs.uiuc.edu
>>>>>>>>>>>>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
>>>>>>>>>>>>> _______________________________________________
>>>>>>>>>>>>> llvm-commits mailing list
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