[eigen] InnerPanel change mis-detects alignment?

[Jitse Niesen <jitse@xxxxxxxxxxxxxxxxx>]

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