In Fortran applications, by default, scalar arguments are passed by reference. Therefore, in SIMD-enabled functions, arguments are passed as a short vector of addresses instead of a single address. The compiler then gathers data from the vector of addresses to create a short vector of values for use in subsequent vector arithmetic. This gather activity negatively impacts performance. To fix: Add a LINEAR clause with a REF modifier (introduced in OpenMP* 4.5) to your vector declaration. Specifically, add LINEAR (REF(linear-list[: linear-step])) to your !$OMP DECLARE SIMD directive.