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by jcelerier 1931 days ago
LLVM can just put the compiled code at some place in your ram and then you can just execute it
2 comments
Const-me 1931 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 1931 days ago
... yes ? https://github.com/weliveindetail/JitFromScratch
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Const-me 1931 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 1930 days ago
> Still, LLVM is a huge dependency to redistribute.

But .NET isn't?

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Const-me 1930 days ago
> But .NET isn't?

Indeed.

.NET runtime takes about 30 MB, or 50 MB if you're on Windows and need desktop components. Links there: https://dotnet.microsoft.com/download/dotnet/5.0

clang+llvm package takes 300-400 MB, that's almost an order of magnitude difference: https://github.com/llvm/llvm-project/releases/tag/llvmorg-11...

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jcelerier 1930 days ago
> clang+llvm package takes 300-400 MB, that's almost an order of magnitude difference

I ship a statically compiled llvm + clang with my software and it does not add 300-400 mb to the binary at all, only something like 20-30 mb.

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namibj 1931 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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