Comment by DanielHB

I wrote a few benchmarks a few years ago comparing JS vs C++ compiled to WASM vs C++ compiled to x64 with -O3.

I was surprised that the heaviest one (a lot of float math) run about the same speed in JS vs C++ -> x64. The code was several nested for loops manipulating a buffer and using only local-scoped variables and built-in Math library functions (like sqrt) with no JS objects/arrays besides the buffer. So the code of both implementations was actually very similar.

The C++ -> WASM version of that one benchmark was actually significantly slower than both the JS and C++ -> x64 version (again, a few years ago, I imagine it got better now).

Most compilers are really good at optimizing code if you don't use the weird "productivity features" of your higher level languages. The main difference of using lower level languages is that not being allowed to use those productivity features prevents you from accidentally tanking performance without noticing.

I still hope to see the day where a language could have multiple "running modes" where you can make an individual module/function compile with a different feature-set for guaranteeing higher performance. The closest thing we have to this today is Zig using custom allocators (where opting out of receiving an allocator means no heap allocations are guaranteed for the rest of the stack call) and @setRuntimeSafety(false) which disables runtime safety checks (when using ReleseSafe compilation target) for a single scope.