> LuaJITted Lua code runs at 80% (on average, sometimes faster!) of the compiled C version of the same algorithm, typically
Cannot confirm this. It might be true on selected micro benchmarks. Here are the results of the Are-we-fast-yet benchmark suite, which includes a decent set of benchmarks challenging CPU, cache and memory access: https://github.com/rochus-keller/Oberon/blob/master/testcase....
On average, the C and C++ implementations are five times faster than LuaJIT.
> There are also some neat languages that compile to (transpile to?) Lua
Here is a comprehensive list: https://github.com/hengestone/lua-languages. Lanuages like Oberon or Luon directly compile to LuaJIT bytecode (i.e. not to Lua).
The code in Are-we-fast-yet has been heavily optimized. It might still be true that naive LuaJIT can run almost as fast as Naive C.
Have a look at the results and the code; there are benchmarks in the suite where the (ideomatic) C/C++ implementation is "only" twice as fast as the corresponding (idiomatic) Lua implementation, but on average (geomean of all factors) it's about five times as fast. The guidelines of the benchmark are pretty strict to enable fair comparisons (see https://github.com/smarr/are-we-fast-yet/blob/master/docs/gu...).
I looked at the docs. This seems to be comparing against Lua, which is why I specifically said LuaJIT
This is quite a distinction to be made. Can you clarify?
Directly from their guidelines page:
Lua
We write code compatible with Lua 5.1, 5.2 and 5.3.
Smalltalk/Ruby symbols are represented as normal strings.
We use Lua 1-based array and the length operator #.
We use single object when a class is not required.
Bitwise operators with various Lua versions is a nightmare.
We use luacheck as a linter.
It's essentially written in Lua 5.1 with specific alternative implementations of mandelbrot and hashindextable for Lua 5.3 selectable by the test runner. But this doesn't matter much because my reference is LuaJIT. I have also compared different LuaJIT and also PUC Lua implementations, see http://software.rochus-keller.ch/are-we-fast-yet_LuaJIT_2017... and http://software.rochus-keller.ch/are-we-fast-yet_Lua_results....