[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 06:12:43 PST 2012
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");
}
-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.
>>>>>>>>>>>>
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