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

Calculating dependencies ... done!
Dependency resolution took 1.51 s (backtrack: 0/20).

[ebuild     U  ] dev-libs/gmp-6.3.0-r2:0/10.4::gentoo [6.3.0-r1:0/10.4::gentoo] USE="asm cpudetection cxx -doc -pic -static-libs -verify-sig" 2046 KiB

Total: 1 package (1 upgrade), Size of downloads: 2046 KiB