extra_math/build.rs

//! Build script for compiler feature detection
use std::env;

fn main() {
    #[cfg(all(feature = "unstable"))]
    {
        // Feature detection whether native f16/f128 support works
        // This is taken from https://github.com/rust-lang/rust/blob/master/library/std/build.rs
        println!("cargo:rerun-if-changed=build.rs");
        let target_arch =
            env::var("CARGO_CFG_TARGET_ARCH").expect("CARGO_CFG_TARGET_ARCH was not set");
        let target_os = env::var("CARGO_CFG_TARGET_OS").expect("CARGO_CFG_TARGET_OS was not set");
        let target_vendor =
            env::var("CARGO_CFG_TARGET_VENDOR").expect("CARGO_CFG_TARGET_VENDOR was not set");
        let target_pointer_width: u32 = env::var("CARGO_CFG_TARGET_POINTER_WIDTH")
            .expect("CARGO_CFG_TARGET_POINTER_WIDTH was not set")
            .parse()
            .unwrap();
        let is_miri = env::var_os("CARGO_CFG_MIRI").is_some();
        // Emit these on platforms that have no known ABI bugs, LLVM selection bugs, lowering bugs,
        // missing symbols, or other problems, to determine when tests get run.
        // If more broken platforms are found, please update the tracking issue at
        // <https://github.com/rust-lang/rust/issues/116909>
        //
        // Some of these match arms are redundant; the goal is to separate reasons that the type is
        // unreliable, even when multiple reasons might fail the same platform.
        println!("cargo:rustc-check-cfg=cfg(reliable_f16)");
        println!("cargo:rustc-check-cfg=cfg(reliable_f128)");

        // This is a step beyond only having the types and basic functions available. Math functions
        // aren't consistently available or correct.
        println!("cargo:rustc-check-cfg=cfg(reliable_f16_math)");
        println!("cargo:rustc-check-cfg=cfg(reliable_f128_math)");

        let has_reliable_f16 = match (target_arch.as_str(), target_os.as_str()) {
            // We can always enable these in Miri as that is not affected by codegen bugs.
            _ if is_miri => true,
            // Selection failure until recent LLVM <https://github.com/llvm/llvm-project/issues/93894>
            // FIXME(llvm19): can probably be removed at the version bump
            ("loongarch64", _) => false,
            // Selection failure <https://github.com/llvm/llvm-project/issues/50374>
            ("s390x", _) => false,
            // Unsupported <https://github.com/llvm/llvm-project/issues/94434>
            ("arm64ec", _) => false,
            // MinGW ABI bugs <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115054>
            ("x86_64", "windows") => false,
            // Apple has a special ABI for `f16` that we do not yet support
            // FIXME(builtins): fixed by <https://github.com/rust-lang/compiler-builtins/pull/675>
            ("x86" | "x86_64", _) if target_vendor == "apple" => false,
            // Missing `__gnu_h2f_ieee` and `__gnu_f2h_ieee`
            ("powerpc" | "powerpc64", _) => false,
            // Missing `__gnu_h2f_ieee` and `__gnu_f2h_ieee`
            ("mips" | "mips32r6" | "mips64" | "mips64r6", _) => false,
            // Missing `__extendhfsf` and `__truncsfhf`
            ("riscv32" | "riscv64", _) => false,
            // Most OSs are missing `__extendhfsf` and `__truncsfhf`
            (_, "linux" | "macos") => true,
            // Almost all OSs besides Linux and MacOS are missing symbols until compiler-builtins can
            // be updated. <https://github.com/rust-lang/rust/pull/125016> will get some of these, the
            // next CB update should get the rest.
            _ => false,
        };

        let has_reliable_f128 = match (target_arch.as_str(), target_os.as_str()) {
            // We can always enable these in Miri as that is not affected by codegen bugs.
            _ if is_miri => true,
            // Unsupported <https://github.com/llvm/llvm-project/issues/94434>
            ("arm64ec", _) => false,
            // ABI and precision bugs <https://github.com/rust-lang/rust/issues/125109>
            // <https://github.com/rust-lang/rust/issues/125102>
            ("powerpc" | "powerpc64", _) => false,
            // Selection bug <https://github.com/llvm/llvm-project/issues/95471>
            ("nvptx64", _) => false,
            // ABI unsupported  <https://github.com/llvm/llvm-project/issues/41838>
            ("sparc", _) => false,
            // MinGW ABI bugs <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115054>
            ("x86_64", "windows") => false,
            // 64-bit Linux is about the only platform to have f128 symbols by default
            (_, "linux") if target_pointer_width == 64 => true,
            // Same as for f16, except MacOS is also missing f128 symbols.
            _ => false,
        };

        // Configure platforms that have reliable basics but may have unreliable math.

        // LLVM is currently adding missing routines, <https://github.com/llvm/llvm-project/issues/93566>
        let has_reliable_f16_math = has_reliable_f16
            && match (target_arch.as_str(), target_os.as_str()) {
                // FIXME: Disabled on Miri as the intrinsics are not implemented yet.
                _ if is_miri => false,
                // x86 has a crash for `powi`: <https://github.com/llvm/llvm-project/issues/105747>
                ("x86" | "x86_64", _) => false,
                // Assume that working `f16` means working `f16` math for most platforms, since
                // operations just go through `f32`.
                _ => true,
            };

        let has_reliable_f128_math = has_reliable_f128
            && match (target_arch.as_str(), target_os.as_str()) {
                // FIXME: Disabled on Miri as the intrinsics are not implemented yet.
                _ if is_miri => false,
                // LLVM lowers `fp128` math to `long double` symbols even on platforms where
                // `long double` is not IEEE binary128. See
                // <https://github.com/llvm/llvm-project/issues/44744>.
                //
                // This rules out anything that doesn't have `long double` = `binary128`; <= 32 bits
                // (ld is `f64`), anything other than Linux (Windows and MacOS use `f64`), and `x86`
                // (ld is 80-bit extended precision).
                ("x86_64", _) => false,
                (_, "linux") if target_pointer_width == 64 => true,
                _ => false,
            };

        if has_reliable_f16 {
            println!("cargo:rustc-cfg=reliable_f16");
        }
        if has_reliable_f128 {
            println!("cargo:rustc-cfg=reliable_f128");
        }
        if has_reliable_f16_math {
            println!("cargo:rustc-cfg=reliable_f16_math");
        }
        if has_reliable_f128_math {
            println!("cargo:rustc-cfg=reliable_f128_math");
        }
    }

    println!("cargo:rustc-check-cfg=cfg(overflow_checks_stable)");

    if std::panic::catch_unwind(|| {
        #[allow(arithmetic_overflow)]
        let _ = 255_u8 + 1;
    })
    .is_err()
    {
        println!("cargo:rustc-cfg=overflow_checks_stable");
    }
}