Re: [eigen] InnerPanel change mis-detects alignment?

[Benoit Jacob <jacob.benoit.1@xxxxxxxxx>]

2010/8/16 Gael Guennebaud <gael.guennebaud@xxxxxxxxx>:
> Hi,
>
> again the issue was not in this change but it existed before.
>
> I've simply removed the AlignedBit flag for non vectorizable scalar
> types and reapplied this changeset.

Thanks! I hadn't understood that the issue was preexistent.
Benoit

>
> cheers,
>
> gael
>
> On Wed, Aug 11, 2010 at 6:14 AM, Benoit Jacob <jacob.benoit.1@xxxxxxxxx> wrote:
>> Hi,
>>
>> I have backed out Gael's changeset for now, so we can quietly take our
>> time to fix this.
>>
>> Many thanks to Jitse, and counting on everyone's understanding. The
>> bug seemed to occur only on certain platforms, e.g. here on linux
>> x86-64 I couldn't reproduce it (and fedora doesn't make it easy to
>> build 32bit binaries).
>>
>> Jitse, I guess this was caught by our unit tests, right? If not,
>> please add your test case as a new unit test.
>>
>> Cheers,
>> Benoit
>>
>> 2010/8/7 Gael Guennebaud <gael.guennebaud@xxxxxxxxx>:
>>> Hi,
>>>
>>> sorry for looking at it only right now. Actually the problem is either
>>> in the assert:
>>>
>>> ei_assert(EIGEN_IMPLIES(ei_traits<Derived>::Flags&AlignedBit,
>>> (size_t(m_data)&0xf)==0)
>>>                 && "data is not aligned");
>>>
>>> MapBase.h line 193, or in the way the AlignedBit flag is assigned.
>>> Indeed, without SSE we have:
>>>
>>> (Matrix3f::Flags & AlignedBit) == AlignedBit (== 64)
>>>
>>> because in this case ei_packet_traits<float>::size == 1.
>>>
>>> Well, maybe there is an issue in both. First, I doubt it makes sense
>>> to set the AlignedBit flags for scalar types which are not vectorized,
>>> and second the hard coded alignment test ((size_t(m_data)&0xf)==0)) is
>>> clearly not satisfactory....
>>>
>>> gael
>>>
>>> On Fri, Jul 30, 2010 at 1:23 PM, Jitse Niesen <jitse@xxxxxxxxxxxxxxxxx> wrote:
>>>> Hello,
>>>>
>>>> Changeset 05aa89b0c8a4 (allow vectorization of mat44.col() by adding a
>>>> InnerPanel boolean), committed about a week ago, breaks quite a number of
>>>> tests on my computer (32bits linux, gcc 4.3.3). Here is a simple example:
>>>>
>>>> -------------------
>>>> #include <Eigen/Core>
>>>> #include <iostream>
>>>> using namespace Eigen;
>>>> using namespace std;
>>>>
>>>> int main()
>>>> {
>>>>  Matrix3f m = Matrix3f::Random();
>>>>  cout << "m = \n" << m << "\n";
>>>>  cout << "m.data() = " << m.data() << "\n";
>>>>  cout << "m.col(0) = \n" << m.col(0) << "\n";
>>>>  return 0;
>>>> }
>>>> -------------------
>>>>
>>>> When compiled with no flags I get the following output
>>>>
>>>> -------------------
>>>> m =
>>>>  0.680375   0.59688 -0.329554
>>>> -0.211234  0.823295  0.536459
>>>>  0.566198 -0.604897 -0.444451
>>>> m.data() = 0xbfe53e38
>>>> eigenfoo: /home/amsta/jitse/scratch/eigen-dev/Eigen/src/Core/MapBase.h:193:
>>>> void Eigen::MapBase<Derived>::checkSanity() const [with Derived =
>>>> Eigen::Block<Eigen::Matrix<float, 3, 3, 0, 3, 3>, 3, 1, true, true>]:
>>>> Assertion `(!(ei_traits<Derived>::Flags&AlignedBit) ||
>>>> ((size_t(m_data)&0xf)==0)) && "data is not aligned"' failed.
>>>> Aborted
>>>> -------------------
>>>>
>>>> It looks like Eigen thinks that m.col(0) is aligned on a 16-byte boundary,
>>>> which it is not. The backtrace produced by gdb is
>>>>
>>>> -------------------
>>>> #0  0x00110402 in __kernel_vsyscall ()
>>>> #1  0x00551fa0 in raise () from /lib/libc.so.6
>>>> #2  0x005538b1 in abort () from /lib/libc.so.6
>>>> #3  0x0054b3ce in __assert_fail () from /lib/libc.so.6
>>>> #4  0x08049814 in Eigen::MapBase<Eigen::Block<Eigen::Matrix<float, 3, 3, 0,
>>>> 3, 3>, 3, 1, true, true> >::checkSanity (this=0xbf9ac120)
>>>>    at /home/amsta/jitse/scratch/eigen-dev/Eigen/src/Core/MapBase.h:192
>>>> #5  0x080498aa in MapBase (this=0xbf9ac120, data=0xbf9ac0f8, rows=3, cols=1)
>>>>    at /home/amsta/jitse/scratch/eigen-dev/Eigen/src/Core/MapBase.h:174
>>>> #6  0x080498ff in Block (this=0xbf9ac120, xpr=@0xbf9ac0f8, i=0)
>>>>    at /home/amsta/jitse/scratch/eigen-dev/Eigen/src/Core/Block.h:252
>>>> #7  0x0804997e in Eigen::DenseBase<Eigen::Matrix<float, 3, 3, 0, 3, 3>
>>>>>::col    (this=0xbf9ac0f8, i=0)
>>>>    at /home/amsta/jitse/scratch/eigen-dev/Eigen/src/Core/Block.h:944
>>>> #8  0x08048cec in main () at eigenfoo.cc:11
>>>> -------------------
>>>>
>>>> This issue disappears when I go back to the revision before changeset
>>>> 05aa89b0c8a4. It also disappears when I compile with -msse2.
>>>>
>>>> I hope this is enough for you to find out what's happening. If not, I can
>>>> have a further look.
>>>>
>>>> Cheers,
>>>> Jitse
>>>>
>>>>
>>>>
>>>
>>>
>>>
>>
>>
>>
>
>
>