Improve performance of CR functions in JIT64

[FioraAeterna]

Use a lookup table instead of calculating it on the fly.

[phire]

Well, it's smaller and neater. But look up tables are known to have surprises on modern CPUs.

I suspect this one is small enough, but I'd like to see benchmarks.

[FioraAeterna]

We already use lookup tables in a bunch of other places (like the quantization/dequantization), so it doesn't seem like anything new, unless I'm missing something?

[neobrain]

@phire what surprises would you be talking about?

Fwiw, if there's even a tiny chance of this PR regressing, I'd prefer if a hwtest covering the whole instruction input range was written (I'll work on a feature to ease writing such tests soon-ish, so maybe wait until that's published).

[phire]

Lookup table is 3-4 cycles if it's an L1 hit and all the other instructions depend on each other. I think it's 7 cycles best case with a worst case in the hundreds of cycles.

The old code has very few dependencies between the blocks, only the ORs depend on each other. I suspect it can do 10 cycles consistently.

Like I said, I'd be interested in benchmarks.

[FioraAeterna]

We use lookup tables in a ton of other cases where constants could be generated on the fly (for cheaper than here), so I don't think this could possibly be any worse... do we have any games that make heavy enough use of these instructions to bench?

[degasus]

@phire Is this lookup tables bigger than the reduced code size? You've missed to code cache miss.

[FioraAeterna]

749 to 736 seconds on POV-RAY benchmark, so 1.7% faster overall.

[Tilka]

lgtm

I'd be interested in a benchmark comparison of this PR with and without the lookup tables.

[Sonicadvance1]

@FioraAeterna: This comment grants you the permission to merge this pull request whenever you think it is ready. After addressing the remaining comments, click this link to merge.

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@dolphin-emu-bot allowmerge

[FioraAeterna]

I'm very slightly nervous about this since some of the variants of these instructions seem incredibly rare, but if something does go wrong, I have a blanket fort prepared to defend myself.