[Bug c++/56564] movdqa on possibly-8-byte-aligned struct with -O3

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56564



Richard Biener <rguenth at gcc dot gnu.org> changed:



           What    |Removed                     |Added

----------------------------------------------------------------------------

             Status|UNCONFIRMED                 |WAITING

   Last reconfirmed|                            |2013-03-08

            Summary|[4.7 Regression] movdqa on  |movdqa on

                   |possibly-8-byte-aligned     |possibly-8-byte-aligned

                   |struct with -O3             |struct with -O3

     Ever Confirmed|0                           |1

      Known to fail|                            |4.6.4, 4.7.2, 4.8.0



--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> 2013-03-08 
10:00:54 UTC ---

This instruction appears in an EH region of function



_ZN5boost16exception_detail27get_static_exception_objectINS0_10bad_alloc_EEENS_13exception_ptrEv



(AFAIK).  It's defined twice, once weak and aligned 8 and once strong

and aligned 16, so AFAIK it _is_ aligned properly.



        .align 8

        .type  

_ZGVZN5boost16exception_detail27get_static_exception_objectINS0_10bad_alloc_EEENS_13exception_ptrEvE2ep,

@gnu_unique_object

        .size  

_ZGVZN5boost16exception_detail27get_static_exception_objectINS0_10bad_alloc_EEENS_13exception_ptrEvE2ep,

8

_ZGVZN5boost16exception_detail27get_static_exception_objectINS0_10bad_alloc_EEENS_13exception_ptrEvE2ep:

        .zero   8

        .weak  

_ZZN5boost16exception_detail27get_static_exception_objectINS0_10bad_alloc_EEENS_13exception_ptrEvE2ep

        .section       

.bss._ZZN5boost16exception_detail27get_static_exception_objectINS0_10bad_alloc_EEENS_13exception_ptrEvE2ep,"awG",@nobits,_ZZN5boost16exception_detail27get_static_exception_objectINS0_10bad_alloc_EEENS_13exception_ptrEvE2ep,comdat

        .align 16

        .type  

_ZZN5boost16exception_detail27get_static_exception_objectINS0_10bad_alloc_EEENS_13exception_ptrEvE2ep,

@gnu_unique_object

        .size  

_ZZN5boost16exception_detail27get_static_exception_objectINS0_10bad_alloc_EEENS_13exception_ptrEvE2ep,

16

_ZZN5boost16exception_detail27get_static_exception_objectINS0_10bad_alloc_EEENS_13exception_ptrEvE2ep:

        .zero   16



and readelf shows:



  [192] .bss._ZZN5boost16 NOBITS           0000000000000000  00001ca0

       0000000000000010  0000000000000000 WAG       0     0     16



with alignment of 16.



> This crashes if

>_ZZN5boost16exception_detail27get_static_exception_objectINS0_10bad_alloc_EEENS_13exception_ptrEvE2ep

> comes from another object file where it is declared with 8-byte alignment.



so this would be a bug and a violation of ODR(?)



What's this "other object file"?



The code piece in question is:



        template <class Exception>

        exception_ptr

        get_static_exception_object()

            {

            Exception ba;

            exception_detail::clone_impl<Exception> c(ba);

            static exception_ptr ep(shared_ptr<exception_detail::clone_base

const>(new exception_detail::clone_impl<Exception>(c)));

            return ep;

            }



OTOH, not sure what increases the alignment of that object from it's

type-alignmend.



Same alignment is emitted with 4.8 and also 4.6 - so you must be unlucky

with that other object file (compiled with which compiler?)



Please also attach preprocessed source of the "other object file"