For column-major matrices A*B, with A complex and B real would be equivalent to multiplying two real matrices where A has twice the height. Currently, Eigen is not able to vectorize this properly. Actually, clang is able to auto-vectorize this (for full FMA usage, sometimes this requires -ffast-math): https://godbolt.org/z/ILd8tL
I guess complex*real could easially be solved by Bug 1019.
But real*complex will require some new logic (essentially, the real matrix would need to have each row duplicated).
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