Move header-only C++ runtime to dedicated runtime library - #103

Compilation-time benchmark

I tested the generated C++ compilation time before and after the pre-built GenWasm runtime refactor.

The benchmark compares:

• Before: header-only runtime
• After: pre-built libgenwasym

For each test case, I measured the direct clang++ compile/link time of the generated C++ code. Each value is the average of 3 runs on the same machine. The benchmark does not include sbt, C++ generation time, generated executable runtime, or the one-time runtime library build time.

I tested both -O0 and -O3.

-O0

-O3

Across the controlled test cases, I did not observe a compilation-time regression after moving the runtime to the pre-built library. The pre-built runtime reduced generated C++ compile/link time in all tested cases, with the largest improvement appearing for the large small-snapshot-concrete workload under -O3.

Note: fact - concrete generated different C++ between the header-only and pre-built versions, so its timing is included for completeness.

I attached the benchmark script below so the same comparison can be reproduced:
benchmark_genwasym_compile.sh

Thanks @Pennnnnnnny and @butterunderflow! This looks like a good improvement in compilation time, can you also list the size of these C++ files as well as the number of C++ files? Another thing I noticed is that the headers still include some immer/* headers, is it necessary? I think we should be able to move all immer-related code into the runtime lib, and I guess that would further improve compilation time.

It would be good to also separate interfaces for the generated code, and interfaces for the runtime itself, so that we can minimize the header exposed to the generated code. For example, in GenSym, the former is quite a compact header file https://github.com/Generative-Program-Analysis/GenSym/blob/main/headers/gensym/runtime.hpp, which doesn't rely on immer, and the header for the runtime is https://github.com/Generative-Program-Analysis/GenSym/blob/main/headers/gensym.hpp, which includes everything that used to be in the monolithic header.