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vfpu branch in delay slot #1926

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unknownbrackets opened this issue May 26, 2013 · 3 comments · Fixed by #3175
Closed

vfpu branch in delay slot #1926

unknownbrackets opened this issue May 26, 2013 · 3 comments · Fixed by #3175

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@unknownbrackets
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I found a game (Disgaea 2) that does some vfpu stuff and then:

vcmp.q GT, C310, C300
bvt addr1(CC[0])
bvt addr1(CC[1])
bvt addr1(CC[2])
bvt addr1(CC[3])

---

We should probably test this. I did a quick search and there's a comment in JPCSP's code that says they insert a nop in between. But I wonder what order it actually executes in, if they are different addresses... or if they have to be the same or something.

-[Unknown]
@hrydgard
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Wow that's some scary code, I wonder what possessed them to write that...

I would also guess that inserting nops (ignoring the delay slots) is likely the way to go here, but yes, should definitely test.

@unknownbrackets
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So far only that game:
http://report.ppsspp.org/temp/recent/kind/161

But also:
http://report.ppsspp.org/temp/recent/kind/163

Here's another scary one (but maybe just a test since it doesn't have a game id):
http://report.ppsspp.org/temp/recent/kind/158

-[Unknown]

@unknownbrackets
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Armjit crashes when this happens (infinite loop.) Affects at least Zettai Hero Project and Disgaea 2 (#1679.)

-[Unknown]

unknownbrackets added a commit to unknownbrackets/ppsspp that referenced this issue Jun 3, 2013
@unknownbrackets
Bail out on a delay slot in VFPU on arm also.
a640ac4 
Otherwise we loop infinitely.

Workaround for hrydgard#1926.  Should fix hrydgard#1679.
@unknownbrackets unknownbrackets mentioned this issue Jun 3, 2013
Merged
unknownbrackets added a commit to unknownbrackets/ppsspp that referenced this issue Aug 15, 2013
@unknownbrackets
Handle branches in VFPU delay slots better.
e639f8d 
Based on tests on a PSP, all branches are attempted.  The behavior is
technically undefined.

It seems to take the delay slot's target if they differ and both pass.
This is the behavior the interpreter has, but it's more work in jit.

Since only a couple games seem to do this, and clearly expect this
behavior, this fixes all known cases of hrydgard#1926.
@unknownbrackets unknownbrackets mentioned this issue Aug 15, 2013
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@unknownbrackets unknownbrackets mentioned this issue Jan 26, 2021
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Handle branches in VFPU delay slots better unknownbrackets/ppsspp
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@hrydgard @unknownbrackets