After v2.6.1, the configuration of openmp has been improved, which is more simplified and unified. We no longer need to configure additional rules. The same effect can be achieved only through a common openmp package.

add_requires("openmp")
target("loop")
     set_kind("binary")
     add_files("src/*.cpp")
     add_packages("openmp")

Before v2.5.9

add_requires("libomp", {optional = true})
target("loop")
    set_kind("binary")
    add_files("src/*.cpp")
    add_rules("c++.openmp")
    add_packages("libomp")

If it is c code, you need to enable ʻadd_rules("c.openmp")`. If it is c/c++ mixed compilation, then these two rules must be set.