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build: Only replace cl.exe with clang-cl for ARM64 Windows builds #2216

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build: Only replace cl.exe with clang-cl for ARM64 Windows builds #2216

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b16e53e
build: Only replace `cl.exe` with `clang-cl` for ARM64 Windows builds
MarijnS95 Jan 10, 2025
612555f
TEST: Drop warnings until we have numeric error codes (out of CI?)
MarijnS95 Mar 31, 2025
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4 changes: 3 additions & 1 deletion BUILDING.md
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Original file line number Diff line number Diff line change
Expand Up @@ -22,9 +22,11 @@ edition of Visual Studio, like Community, Standard, or Enterprise). The
“Desktop development with C++” workflow must be installed. Visual Studio
2022 Version 17.5 is supported; earlier versions of Visual Studio may work.

### (Cross-)compiling to Windows ARM64

For Windows ARM64 targets (aarch64-pc-windows-msvc), the Visual Studio Build
Tools “VS 2022 C++ ARM64 build tools” and "clang" components must be installed.
Add Microsoft's provided version of `clang` to `%PATH%`, which will allow the
Add Microsoft's provided version of `clang-cl` to `%PATH%`, which will allow the
build to work in GitHub Actions without installing anything:
```
$env:Path += ";C:\Program Files (x86)\Microsoft Visual Studio\2022\Enterprise\VC\Tools\Llvm\x64\bin"
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Is this where clang-cl lives?

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It's part of the LLVM toolchain. On Linux machines, yes. On Windows: probably?

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27 changes: 13 additions & 14 deletions build.rs
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Expand Up @@ -148,12 +148,8 @@ fn cpp_flags(compiler: &cc::Tool) -> &'static [&'static str] {
NON_MSVC_FLAGS
} else {
static MSVC_FLAGS: &[&str] = &[
"/Gy", // Enable function-level linking.
"/Zc:wchar_t",
"/Zc:forScope",
"/Zc:inline",
// Warnings.
"/Wall",
"/std:c11", "/Gy", // Enable function-level linking.
"/Wall", // Warnings
"/wd4127", // C4127: conditional expression is constant
"/wd4464", // C4464: relative include path contains '..'
"/wd4514", // C4514: <name>: unreferenced inline function has be
Expand Down Expand Up @@ -559,9 +555,15 @@ fn obj_path(out_dir: &Path, src: &Path) -> PathBuf {

fn configure_cc(c: &mut cc::Build, target: &Target, c_root_dir: &Path, include_dir: &Path) {
let compiler = c.get_compiler();
// FIXME: On Windows AArch64 we currently must use Clang to compile C code
let compiler = if target.os == WINDOWS && target.arch == AARCH64 && !compiler.is_like_clang() {
let _ = c.compiler("clang");
let is_msvc_not_clang_cl = compiler.is_like_msvc() && !compiler.is_like_clang_cl();

// FIXME: On Windows AArch64, ring C code cannot be compiled using cl.exe, but must be compiled
// using the LLVM toolchain. Use clang-cl, which is compatible with flags that are already in
// place (i.e. custom CFLAGS that the user provided to cc).
let compiler = if target.os == WINDOWS && target.arch == AARCH64 && is_msvc_not_clang_cl {
// FIXME: This requires clang-cl to be available in PATH, regardless of any explicit
// or custom path that the user might have provided to cc via the CC flag.
c.compiler("clang-cl");
c.get_compiler()
} else {
compiler
Expand All @@ -584,11 +586,8 @@ fn configure_cc(c: &mut cc::Build, target: &Target, c_root_dir: &Path, include_d
let _ = c.define("NDEBUG", None);
}

if target.arch == X86 {
let is_msvc_not_clang_cl = compiler.is_like_msvc() && !compiler.is_like_clang_cl();
if !is_msvc_not_clang_cl {
let _ = c.flag("-msse2");
}
if target.arch == X86 && !is_msvc_not_clang_cl {
let _ = c.flag("-msse2");
}

// Allow cross-compiling without a target sysroot for these targets.
Expand Down