This should be a fairly easy merge, assuming I didn’t mess anything up. TL:DR no one uses it and it’s not great.
Boot from DVD Backup is an ancient feature with origins in the Megacommit. Back then, GameCube and Wii games were quite large relative to drives of the time. For example, in 2008, the most common hard drive sizes were 320GB and 512GB. On the 320GB drive I personally had at the time, as little as 42 Wii ISOs could have filled it entirely! And that’s ignoring any other files one might want to put onto a drive. Backup DVDs allowed users to burn relatively cheap DVD media and store their GameCube and Wii dumps in a Dolphin accessible way that didn’t eat into their precious HDD space. It had compromises, even then, but in 2008… I mean honestly users probably wouldn’t even notice those compromises with how Dolphin barely even worked at all back then.
Obviously, today the storage space concerns are not as big of an issue. According to seagate the average hard drive it sells today is 8TB. For typical laptops purchased now, the -minimum- selection for storage is usually 1TB. You can even buy a name brand 4TB external hard drive for $100. GC and Wii ISOs are not as big as they once were, relatively anyway. Plus flash drives and SD cards are super cheap and way faster than disc drives ever were. For anyone that has limited drive space, removable flash media can fulfill this offloading role far better than backup DVD media ever could.
Also no one has DVD drives anymore. That’s kind of an important detail.
But to see if Booting from DVD Backup even still worked, I decided to give it a try. I have an ASUS BW-16D1HT, a badass Bluray XL reading and burning drive, connected to my Windows 11 Threadripper 5975WX machine. A super fast drive on a super fast machine is as good as it possibly can get for this feature. So I bought a spindle of DVD-Rs, burned a couple of discs and gave it a try. Surprisingly, it does still work. However, as expected, it introduces a lot of stuttering. Testing Prime 1 and Prime 3, in both games stuttering was introduced whenever the DVD Drive had to suddenly seek. Spikes of 50ms occurred constantly, but I observed 150ms and even over 1000ms stutters! The worst was a three second stutter, when loading Elysia in Prime 3. I could even hear the stutters - any time the drive suddenly made a harsh seeking noise, the game would have a hard stutter. It worked but, it has some serious compromises.
Boot from DVD Backup isn’t great, using removable flash media or external hard drives is a FAR better option for anyone with limited storage space today, and no one can even use this feature anymore because their computers don’t even have disc drives. It’s time for Boot from DVD Backup to go!
So I did my best on the cleanup but I’m bound to have left some bits. Especially in translation - I didn’t get any warnings or anything there that could help point me to where to clean that up. Please review!
See the comment added by this commit. We were previously guarding against
overshooting in address calculations, but not against undershooting.
Perhaps someone assumed that the displacement of an x86 loadstore was
treated as unsigned?
Note: While the comment says we can undershoot by up to 2 GiB, in
practice Jit64 as it currently behaves won't actually undershoot by more
than 0x8000 if my analysis is correct. But address space is cheap, so
let's guard the full 2 GiB.
This is the behavior in the x64 and ARM64 vertex loaders. I don't know if it makes sense (the whole skipped vertex system seems jank, but several games behave incorrectly without it).
This generated a warning on GCC about the operation being potentially undefined (-Wsequence-point). I'm not sure if that was actually the case, but either way it is a mistake.
shockdude