I have bit modified your code. get This if useful.

RoundedRectangle(cornerRadius: 3) .stroke(Color(UIColor.label).opacity(0.8), lineWidth: 3) .frame(width: 35, height: 35, alignment: .center) .overlay( VStack(spacing: 2.5) { HStack(spacing: 8) { ForEach(0..<3) { _ in RoundedRectangle(cornerRadius: 3) .stroke(Color.black.opacity(0.8), lineWidth: 1.5) .frame(width: 1, height: 7, alignment: .top) } } .offset(y: -3.5) RoundedRectangle(cornerRadius: 3) .stroke(Color.black.opacity(0.8), lineWidth: 1.5) .frame(height: 1) .padding(.horizontal, 5) Text(date) .font(.system(size: 15)) .fontWeight(.bold) } ,alignment: .top )

Just out of curiosity I've taken a look at what happens under the hood, and I've used [dtruss/strace][1] on each test.
C++
./a.out < in Saw 6512403 lines in 8 seconds. Crunch speed: 814050
syscalls `sudo dtruss -c ./a.out < in`
CALL COUNT __mac_syscall 1 <snip> open 6 pread 8 mprotect 17 mmap 22 stat64 30 read_nocancel 25958

Python
./a.py < in Read 6512402 lines in 1 seconds. LPS: 6512402
syscalls `sudo dtruss -c ./a.py < in`
CALL COUNT __mac_syscall 1 <snip> open 5 pread 8 mprotect 17 mmap 21 stat64 29
[1]: http://en.wikipedia.org/wiki/Strace