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by jcelerier 1929 days ago
> 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.
1 comments
Const-me 1929 days ago
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.

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jcelerier 1929 days ago
LLVM can just put the compiled code at some place in your ram and then you can just execute it
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Const-me 1929 days ago
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.

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jcelerier 1929 days ago
... yes ? https://github.com/weliveindetail/JitFromScratch
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Const-me 1929 days ago
Interesting, I didn’t know llvm is that flexible.

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.

In .NET everything is in the standard library. The generated code is even platform-independent, for no additional overhead. Here’s couple non-trivial examples: https://github.com/Const-me/ComLightInterop/blob/master/ComL... https://github.com/Const-me/ComLightInterop/blob/master/ComL...

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SubjectToChange 1928 days ago
> Still, LLVM is a huge dependency to redistribute.

But .NET isn't?

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namibj 1929 days ago
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.

[0]: http://terralang.org/

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