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    //! ARM C Language Extensions (ACLE)
    //!
    //! # Developer notes
    //!
    //! Below is a list of built-in targets that are representative of the different ARM
    //! architectures; the list includes the `target_feature`s they possess.
    //!
    //! - `armv4t-unknown-linux-gnueabi` - **ARMv4** - `+v4t`
    //! - `armv5te-unknown-linux-gnueabi` - **ARMv5TE** - `+v4t +v5te`
    //! - `arm-unknown-linux-gnueabi` - **ARMv6** - `+v4t +v5te +v6`
    //! - `thumbv6m-none-eabi` - **ARMv6-M** - `+v4t +v5te +v6 +thumb-mode +mclass`
    //! - `armv7-unknown-linux-gnueabihf` - **ARMv7-A** - `+v4t +v5te +v6 +v6k +v6t2 +v7 +dsp +thumb2 +aclass`
    //! - `armv7r-none-eabi` - **ARMv7-R** - `+v4t +v5te +v6 +v6k +v6t2  +v7 +dsp +thumb2 +rclass`
    //! - `thumbv7m-none-eabi` - **ARMv7-M** - `+v4t +v5te +v6 +v6k +v6t2 +v7 +thumb2 +thumb-mode +mclass`
    //! - `thumbv7em-none-eabi` - **ARMv7E-M** - `+v4t +v5te +v6 +v6k +v6t2 +v7 +dsp +thumb2 +thumb-mode +mclass`
    //! - `thumbv8m.main-none-eabi` - **ARMv8-M** - `+v4t +v5te +v6 +v6k +v6t2 +v7 +thumb2 +thumb-mode +mclass`
    //! - `armv8r-none-eabi` - **ARMv8-R** - `+v4t +v5te +v6 +v6k +v6t2 +v7 +v8 +thumb2 +rclass`
    //! - `aarch64-unknown-linux-gnu` - **ARMv8-A (AArch64)** - `+fp +neon`
    //!
    //! Section 10.1 of ACLE says:
    //!
    //! - "In the sequence of Arm architectures { v5, v5TE, v6, v6T2, v7 } each architecture includes
    //! its predecessor instruction set."
    //!
    //! - "In the sequence of Thumb-only architectures { v6-M, v7-M, v7E-M } each architecture includes
    //! its predecessor instruction set."
    //!
    //! From that info and from looking at how LLVM features work (using custom targets) we can identify
    //! features that are subsets of others:
    //!
    //! Legend: `a < b` reads as "`a` is a subset of `b`"; this means that if `b` is enabled then `a` is
    //! enabled as well.
    //!
    //! - `v4t < v5te < v6 < v6k < v6t2 < v7 < v8`
    //! - `v6 < v8m < v6t2`
    //! - `v7 < v8m.main`
    //!
    //! *NOTE*: Section 5.4.7 of ACLE says:
    //!
    //! - "__ARM_FEATURE_DSP is defined to 1 if the DSP (v5E) instructions are supported and the
    //! intrinsics defined in Saturating intrinsics are available."
    //!
    //! This does *not* match how LLVM uses the '+dsp' feature; this feature is not set for v5te
    //! targets so we have to work around this difference.
    //!
    //! # References
    //!
    //! - [ACLE Q2 2018](https://developer.arm.com/docs/101028/latest)

    // 8, 7 and 6-M are supported via dedicated instructions like DMB. All other arches are supported
    // via CP15 instructions. See Section 10.1 of ACLE
    mod barrier;

    pub use self::barrier::*;

    mod hints;

    pub use self::hints::*;

    mod registers;

    pub use self::registers::*;

    mod ex;

    pub use self::ex::*;

    // Supported arches: 5TE, 7E-M. See Section 10.1 of ACLE (e.g. QADD)
    // We also include the A profile even though DSP is deprecated on that profile as of ACLE 2.0 (see
    // section 5.4.7)
    // Here we workaround the difference between LLVM's +dsp and ACLE's __ARM_FEATURE_DSP by gating on
    // '+v5te' rather than on '+dsp'
    #[cfg(all(
        not(target_arch = "aarch64"),
        any(
            // >= v5TE but excludes v7-M
            all(target_feature = "v5te", not(target_feature = "mclass")),
            // v7E-M
            all(target_feature = "mclass", target_feature = "dsp"),
        )
    ))]
    mod dsp;

    #[cfg(all(
        not(target_arch = "aarch64"),
        any(
            all(target_feature = "v5te", not(target_feature = "mclass")),
            all(target_feature = "mclass", target_feature = "dsp"),
        )
    ))]
    pub use self::dsp::*;

    // Supported arches: 6, 7-M. See Section 10.1 of ACLE (e.g. SSAT)
    #[cfg(all(not(target_arch = "aarch64"), target_feature = "v6",))]
    mod sat;

    #[cfg(all(not(target_arch = "aarch64"), target_feature = "v6",))]
    pub use self::sat::*;

    // Deprecated in ACLE 2.0 for the A profile but fully supported on the M and R profiles, says
    // Section 5.4.9 of ACLE. We'll expose these for the A profile even if deprecated
    #[cfg(all(
        not(target_arch = "aarch64"),
        any(
            // v7-A, v7-R
            all(target_feature = "v6", not(target_feature = "mclass")),
            // v7E-M
            all(target_feature = "mclass", target_feature = "dsp")
        )
    ))]
    mod simd32;

    #[cfg(all(
        not(target_arch = "aarch64"),
        any(
            all(target_feature = "v6", not(target_feature = "mclass")),
            all(target_feature = "mclass", target_feature = "dsp")
        )
    ))]
    pub use self::simd32::*;

    mod sealed {
        pub trait Dmb {
            unsafe fn __dmb(&self);
        }

        pub trait Dsb {
            unsafe fn __dsb(&self);
        }

        pub trait Isb {
            unsafe fn __isb(&self);
        }

        pub trait Rsr {
            unsafe fn __rsr(&self) -> u32;
        }

        pub trait Rsr64 {
            unsafe fn __rsr64(&self) -> u64;
        }

        pub trait Rsrp {
            unsafe fn __rsrp(&self) -> *const u8;
        }

        pub trait Wsr {
            unsafe fn __wsr(&self, value: u32);
        }

        pub trait Wsr64 {
            unsafe fn __wsr64(&self, value: u64);
        }

        pub trait Wsrp {
            unsafe fn __wsrp(&self, value: *const u8);
        }
    }

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