> They are extremely complex, and were not designed for the use case e.g. relatively slow (designed to run offline on fast developer’s computers, or on even faster build servers).
in 2021 bundling clang along with your program is actually reasonable - if you are compiling small functions without two tons of headers it's measured in milliseconds.
I never tried to, but I think integration of runtime-generated native code gonna cause overhead.
Where do you place these functions once compiled? Into a separate DLL/each?
In .NET it’s quite easy to generate code that calls manually written functions, or access data provided by manually-written stuff. JIT runtime doesn’t treat generated code as something special, e.g. may inline calls across runtime-generated and manually written pieces of the program. With clang you gonna need a layer of indirection to integrate, with function pointers and such.
Processors need addresses of things. Look at the following code https://godbolt.org/z/PYEqKn note the function uses another symbol, “func.counter”.
Shared libraries include relocation tables https://en.wikipedia.org/wiki/Relocation_%28computing%29 with all code locations which needs patching. That’s how the OSes can load them into arbitrary locations in memory and the code will still work.
Still, LLVM is a huge dependency to redistribute. And probably has many points of failure. For instance, I expect you gonna need to watch for INCLUDE and PATH environment variables when using that thing.
If you’re willing to compile, ship and support custom builds of .NET runtime, gonna be less than 20-30 MB.
coreclr.dll (the runtime) is 4.9 MB, clrjit.dll (JIT compiler) is 1.3 MB. The rest is mostly standard libraries, the largest piece of that is System.Private.CoreLib.dll at 9 MB. The numbers are for Win64 version of .NET 5.0.2.
Another thing, for .NET apps the runtime is required anyway, the overhead for runtime code generation is zero.
For C++ apps, llvm + clang (or an equivalent) is only needed on developer’s computers, not something you’d normally ship.
I'll give Terra[0] as an example for something relatively high-level that uses LLVM as a JIT. It can also be used as an AoT compiler with fancy macro stuff in place of the C preprocessor.
in 2021 bundling clang along with your program is actually reasonable - if you are compiling small functions without two tons of headers it's measured in milliseconds.