These are the packages that would be merged, in order:

Calculating dependencies ... done!
Dependency resolution took 0.96 s (backtrack: 0/20).

[ebuild  N     ] sci-mathematics/gmp-ecm-7.0.6-r1::gentoo  USE="custom-tune openmp" CPU_FLAGS_X86="sse2" 949 KiB

Total: 1 package (1 new), Size of downloads: 949 KiB