[llvm-commits] [LLVM, PR11652 PATCH]: Fixed Bug 11652 - assertion failures when Type.cpp is compiled with -Os

[Duncan Sands]

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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