Improve JIT compatibility

[amyren1966]

JIT seem to break compatibility also for system friendly applications.
I notice this specially for programs made with Hollywood. RNOpdf is one example, as the script will fail (stack overflow) if launched when JIT is enabled.
Also games made with Hollywood does fail, or act strange if JIT is on. This is the case for one of my own games, Runaway.
They run fine when JIT is off, but quite slow.
For comparisation, these apps and games does run fine on WinUAE with JIT.

So the feature request is as described in the title.

[midwan]

@amyren1966
Thanks for reporting this. I also have a few Hollywood apps I can test with, so have a scenario to recreate this with.

Normally it's TomB who's doing the JIT and low-level work, so if we can have a scenario to recreate the problem, I can open an issue with him afterwards. ;)

[midwan]

@amyren1966
My Hollywood apps didn't seem to have a problem with JIT.

I'm assuming you're referring to this RunAway game? http://os4.aminet.net/package/game/wb/Runaway_OS3

I could run it normally in my installation, what kind of unexpected behavior did you notice?

[amyren1966]

If JIT is on, the searchlight will stop moving after a while, and stay on just beside the position next to the barell. I guess that the sprite hangs at this position, while the real position is towards the barell. The player can now pass the light without being detected. Also the two guards will stop moving at certain positions. That is, they do move, but the sprites freezes at certain points for a while.

One of my other Hollywood game, donkey kong does work normally, and also one other Hollywood app I did try.
But the RNOpdf app does crash for me if JIT is on. Did you try that one?

[midwan]

@amyren1966
I just tested RNOpdf with the Hollywood.pdf file (3.84 MB), on my AmigaOS 3.1.4.1 installation:

• The 68k version worked normally
• The FPU version showed an error (stack overflow) as you described.

Can you confirm the same with the other Hollywood apps you've tested with?

[midwan]

I've opened an issue at Tom's repo about this: PandTomB/uae4arm#7

[amyren1966]

I confirm that non-FPU version of RNOPdf starts up when JIT enabled. FPU version will fail with JIT.

But my Runaway game is not compiled as a FPU version, and it will not work properly when JIT is enabled. The easiest way to spot this is by launching it, and wait. The searchligt will start moving, from the right side to the left, and then turn back. It will then stop before reaching the right side.
If launched with JIT turned off it will continue moving.

Also I did test my other game, Donkey Kong (also an LCD conversion). This does not use FPU either.
It will lauch and you can start playing. But if you start it (press "1" on the keyboard, or press the A button), then move 3 to 4 steps to the right, and then step back to the left using the arrow keys.
The player will stop moving at one point, and the barells will pass you without generating a miss.
Do this immidiately after pressing "1", then you should be able to test it without getting hit by the barells (or else you might just jump over a few barells first and wait until the path is clear).
If JIT is disabled, the player will move as it should.

By the way. This is on OS3.9, 68030 / AGA chipset, but running on a P96 screen. I also tried testing it with 68020, same thing.

[midwan]

Thanks! I also noticed that disabling JIT FPU doesn't make a difference, so the problem is somewhere in the main JIT code, not the FPU specific part.

Let's give Tom some time to look into this.

[Andiweli]

I don‘t know if it‘s the same issue, but playing Jim Power gives me sprites on wrong positions and faulty collisions. Playing without JIT seems to be correct but hell slow and sound stuttering.

[midwan]

@Andiweli
Games and JIT are usually not a good combination, though there may be some exceptions (those that don't use the custom chipset but really want CPU power).
Jim Power is kind of a special case, works normally on the RPI4 but on lower powered systems it works properly only with frameskip.

[midwan]

Fixed with e0cd52c

[amyren1966]

I notice this issue have been closed. But I still encounter the same issues with JIT enabled.
Is this covered by another thread?