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

[Stepan Dyatkovskiy]

Hi Duncan, can I use DataTypes.h instead?
-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
>>>>>>>>>        llvm-commits at cs.uiuc.edu
>>>>>>>>>        http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits