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

Calculating dependencies ... done!
Dependency resolution took 1.52 s (backtrack: 0/20).

[ebuild     UD ] dev-util/google-perftools-2.15:0/4::gentoo [2.17.2:0/4::gentoo] USE="debug -llvm-libunwind -minimal -optimisememory -pagesize-16k -pagesize-32k -pagesize-64k -pagesize-128k -pagesize-256k -static-libs -test" 868 KiB

Total: 1 package (1 downgrade), Size of downloads: 868 KiB