Content ID caching in Lua

[TurkeyMcMac]

I suggested this in #12438, where you can find some context/rationale. An alternative to this PR is to incorporate its changes into #12438.

To do

This PR is Ready for Review.

How to test

There's a unit test. You can also try the change with other mods that access raw content IDs.

[TurkeyMcMac]

Closing since equivalent functionality is being implemented in #12438.

[TurkeyMcMac]

I'll reopen this as it seems the other PR isn't very active anyway.

[Desour]

👍 For concept.
Code looks fine.
Haven't tested.
You could do a small benchmark to verify that it's faster.

[Desour]

Same as above.

[TurkeyMcMac]

Should I add a setting to disable this, in case people want to save memory? At the most, it could use on the order of one megabyte per thread. Might that be significant on Raspberry Pi servers?

[sfan5]

No. There are much more impactful things that could be tweaked to save RAM.

[rubenwardy]

This needs to be benchmarked to ensure the performance increase is worth the added code

[TurkeyMcMac]

I added benchmark commands. Here are the results on my computer:

	LuaJIT 2.1.0-beta3		PUC Lua 5.1.5
	get_content_id	get_name_from_content_id	get_content_id	get_name_from_content_id
Without cache	27ms	18ms	37ms	24ms
With cache	10ms	7ms	22ms	17ms

[SmallJoker]

What's the benefit of an additional content ID cache? When used heavily, such as in Lua mapgens, the content IDs are already cached by the mod where needed to speed up generation time. This does get rid of the function call entirely inside the 3D (or more) loop to iterate through the data entries.

I very much believe in the "keep it simple, stupid" principle and I don't think this PR fits into that scheme. No optimization helps if mods are programmed inefficiently.

[TurkeyMcMac]

The original use case was a faster implementation of get_node: #12438. The cache is also used in #12609 and #12611. The same cache might as well be used for other parts of the API.

[sfan5]

(code review only this time)

[sfan5]

before:

Time: 7.07 ms
Time: 18.43 ms

after:

Time: 1.11 ms
Time: 2.55 ms