Yeah, I tried my hand at adding amd64_win support to QBE, but going through the very dense code was a slog. I kept refactoring and commenting it just to make heads or tails of it, but ultimately realized I would never be able to minify it back to something upstreamable. I applaud Scott Graham's perseverance and tenacity.

Quentin took pity on me and let me upstream amd64_win with my lengthy variable names and including chatty comments. :)

SysV and Win x64 differ enough that the Windows code is mostly unrelated to/detached from the other backends, so it doesn't feel (too) awful for it to have its own idiosyncratic style.