INTEL-MPI version 19 slower than INTEL-MPI version 18

Problem

An executable build with:

module load intel/19.0.3 impi/2019.3

is up to 20% slower than an executable build with identical code and optimisation, compared with

module load intel/18.0.5 impi/2018.4

Mostly affects code pieces are dominated by communication, but also serial code is affected.

Solution

Stay, if possoble, with the mpi version 18.

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