[Bug c++/115968] g++ 12 and above incorrectly optimize the code with Eigen (-O2 or -O1)

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115968

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
See C++11 and the auto keyword section of
https://eigen.tuxfamily.org/dox/TopicPitfalls.html


The problem is that eval() returns a temporary object (in this case a MatrixXd)
which is then referenced by the Transpose<> expression. However, this temporary
is deleted right after the first line, and then the C expression references a
dead object.