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Support $LLVM_VERSION, $LLVM_TARGETS, and $LLVM_LDFLAGS #15091

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Support $LLVM_VERSION, $LLVM_TARGETS, and $LLVM_LDFLAGS #15091

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HertzDevil
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@HertzDevil HertzDevil commented Oct 17, 2024 •
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Resolves part of #14376.

This may also address part of #15074 since we can now override LLVM_VERSION for the Makefiles as well.

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I'm wondering about the usefulness of LLVM_LDFLAGS. Effectively, you can just pass extra linker flags via --link-flags. I suppose the only purpose would be to suppress flags from llvm_VERSION and llvm-config --libs. But at that point it might just be reasonable to use neither of them and provide version (and targets) explicitly via env var and specify --link-flags.
This is just an observation, asking if it resonates with aynone. I'm not entirely sure about covering all use cases.

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On POSIX environments you can probably pass LLVM_CONFIG=true to suppress all the default configuration too (the Makefiles can be easily adjusted for this).

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Maybe we could drop all those linker flags whenever cross-compiling, but I found that there is no way to tell in Crystal code whether we are also doing the cross-linking on the same host (i.e. --target without --cross-compile), since --cross-compile doesn't add any flags.

@HertzDevil HertzDevil mentioned this pull request Oct 20, 2024
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straight-shoota pushed a commit that referenced this pull request Oct 21, 2024
@HertzDevil
Make Makefile work on MSYS2 (#15102)
b10f171 
* Uses `llvm-config` instead of `llvm_VERSION` for the `x86_64-windows-gnu` target. Also invokes the `find-llvm-config` script using `sh` explicitly and ensures the script returns a Windows path. (This pretty much means a MinGW-w64-based compiler will require the entire MSYS2 environment to work.)
* Increases the stack size from the default 2 MiB to 8 MiB, consistent with builds using the MSVC toolchain.
* `Makefile` and the `bin/crystal` script now recognize `.build/crystal.exe` as the local compiler under MSYS2.
* If `.build/crystal.exe` already exists and we are on Windows, `Makefile` now builds a temporary executable first, just like in `Makefile.win`.
* Ensures `Makefile` doesn't interpret backslashes in `llvm-config.exe`'s path as escape sequences.
* Adds a separate `install_dlls` target for installing the compiler's dependent DLLs to the given prefix's `bin` directory. This is only needed if the installation is to be distributed outside MSYS2.
* Detects the presence of `lld` which can be installed using the `mingw-w64-ucrt-x86_64-lld` package.

With this patch, cross-compiling from MSVC-based Crystal will no longer work until #15091 is merged. Instead it can be done from Linux, including WSL, assuming the host and target LLVM versions are identical (right now MSYS2 has 18.1.8):

```sh
# on Linux
make clean crystal && make -B target=x86_64-windows-gnu

# on MSYS2's UCRT64 environment
pacman -Sy \
  mingw-w64-ucrt-x86_64-gcc mingw-w64-ucrt-x86_64-pkgconf \
  mingw-w64-ucrt-x86_64-gc mingw-w64-ucrt-x86_64-pcre2 mingw-w64-ucrt-x86_64-libiconv \
  mingw-w64-ucrt-x86_64-zlib mingw-w64-ucrt-x86_64-llvm
cc .build/crystal.obj -o .build/crystal.exe \
  $(pkg-config bdw-gc libpcre2-8 iconv zlib --libs) \
  $(llvm-config --libs --system-libs --ldflags) \
  -lDbgHelp -lole32 -lWS2_32 -Wl,--stack,0x800000
```
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@HertzDevil @straight-shoota