4 ms·

LLVM can just put the compiled code at some place in your ram and then you can just execute it

Const-me 6y ago
Processors need addresses of things. Look at the following code https://godbolt.org/z/PYEqKn 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 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.
- jcelerier 6y ago
  ... yes ? https://github.com/weliveindetail/JitFromScratch https://github.com/weliveindetail/JitFromScratch
  - Const-me 6y 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/ComLight/Emit/Proxy.standard.cs https://github.com/Const-me/ComLightInterop/blob/master/ComL... https://github.com/Const-me/ComLightInterop/blob/master/ComLight/Emit/Proxy.custom.cs https://github.com/Const-me/ComLightInterop/blob/master/ComL...
    - SubjectToChange 6y ago
      > Still, LLVM is a huge dependency to redistribute. But .NET isn't?
      - Const-me 6y 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 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-11.0.1 https://github.com/llvm/llvm-project/releases/tag/llvmorg-11...
        jcelerier 6y 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.
        Const-me 6y ago
        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.
        jcelerier 6y ago
        > For C++ apps, llvm + clang (or an equivalent) is only needed on developer’s computers, not something you’d normally ship. unless you want to JIT-compile C++ code at runtime which is the original point.
namibj 6y 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/ http://terralang.org/

Processors need addresses of things. Look at the following code https://godbolt.org/z/PYEqKn 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 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.

jcelerier 6y ago
... yes ? https://github.com/weliveindetail/JitFromScratch https://github.com/weliveindetail/JitFromScratch
- Const-me 6y 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/ComLight/Emit/Proxy.standard.cs https://github.com/Const-me/ComLightInterop/blob/master/ComL... https://github.com/Const-me/ComLightInterop/blob/master/ComLight/Emit/Proxy.custom.cs https://github.com/Const-me/ComLightInterop/blob/master/ComL...
  - SubjectToChange 6y ago
    > Still, LLVM is a huge dependency to redistribute. But .NET isn't?
    - Const-me 6y 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 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-11.0.1 https://github.com/llvm/llvm-project/releases/tag/llvmorg-11...
      - jcelerier 6y 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.
        Const-me 6y ago
        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.
        jcelerier 6y ago
        > For C++ apps, llvm + clang (or an equivalent) is only needed on developer’s computers, not something you’d normally ship. unless you want to JIT-compile C++ code at runtime which is the original point.

namibj 6y 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/ http://terralang.org/