[eigen] Performance regression with Matrix4f multiplication?

[Ryo Miyajima <sergeant.wizard@xxxxxxxxx>]

Hi.

I was testing Matrix4{d,f} multiplication performance across different Eigen versions and found that since 3..3.0, the Matrix4f multiplication speed slowed down significantly when compiled with `-march=native` flag in gcc.

The performance deteriorated on Core i5 and Core i7 but not on a Xeon.

Is this expected behavior (because for example, Eigen optimizes for larger matrices than 4x4), or am I doing something wrong like not providing the right compilation flag?

The benchmarks are in the following repo and can be reproduced by docker images:

https://github.com/sergeant-wizard/eigen_matrix4_benchmark

The assembly code is also provided in the repository.

I searched through bugtracker and this may or may not be related to this issue: http://eigen.tuxfamily.org/bz/show_bug.cgi?id=1342

Thanks in advance for your help.

Ryo Miyajima