Jit64: Don't use fregsIn in HandleNaNs #11139
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fregsIn will include FD for double-precision instructions, since for dependency tracking purposes the instruction does read the upper half of FD. This is not what we want in HandleNaNs. The consequence of this bug is that if an instruction was supposed to output a NaN and FD happens to contain a NaN and FD happens to be the same register as an unused register in the instruction encoding, the NaN in FD could get used as the output instead of the correct NaN. This isn't known to affect any games, which isn't especially surprising considering that there's only one game that needs AccurateNaNs anyway.
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AdmiralCurtiss
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Nov 20, 2022
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Yeah seems fine.
The inconsistent usage of int and u32 for registers bothers me a bit but looking through the code this is far from the only place where it's like that so whatever.
I also wonder if it would be worth it to replace usages of std::vector where the maximum size is a known low value (like here, input is a maximum of 3 values...) with something like a boost static_vector, but that's very much out of scope of this PR.
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fregsIn will include FD for double-precision instructions, since for dependency tracking purposes the instruction does read the upper half of FD. This is not what we want in HandleNaNs.
The consequence of this bug is that if an instruction was supposed to output a NaN and FD happens to contain a NaN and FD happens to be the same register as an unused register in the instruction encoding, the NaN in FD could get used as the output instead of the correct NaN. This isn't known to affect any games, which isn't especially surprising considering that there's only one game that needs AccurateNaNs anyway.