How to manually update the arm64 version of IDL 9.0 on macOS to use newer (faster) Arm Performance Libraries (ArmPL)

The native Apple Silicon (arm64) version of IDL 9.0 uses the Arm Performance Libraries (ArmPL) for Fast Fourier Transforms (FFTs), while the Intel version of IDL uses Intel's Math Kernel Library (MKL). These differing libraries can lead to performance discrepancies between the Intel and arm64 versions of IDL 9.0. In some cases, Intel IDL may perform FFTs faster. However, based on limited testing, if IDL 9.0 is updated to use the latest version of ArmPL as of May 2024 (version 24.04), FFT performance may be improved.


Please follow the instructions below to manually update IDL 9.0 to use a newer version of ArmPL. Future versions of IDL should already include the newer library.



  • IDL 9.0 arm64 version installed on an Apple Silicon (M-series) macOS computer (ONLY 9.0 can be used)
  • Administrator priviledges on your computer
  • Internet connection to download ArmPL installer


WARNING: This updated library hasn't been fully tested for complete compatibility with IDL, but it does appear to work. Proceed at your own risk. 


  1. Rename these four files inside the <idl_dir>/bin/bin.darwin.arm64 directory for backup purposes:
    • libomp.dylib → libomp.dylib.bak
    • libarmpl_mp.dylib → libarmpl_mp.dylib.bak
    • libarmpl_lp64_mp.dylib → libarmpl_lp64_mp.dylib.bak
    • libarmpl.dylib → libarmpl.dylib.bak
  2. Download ArmPL 24.04.
    1. Navigate to https://developer.arm.com/downloads/-/arm-performance-libraries
    2. Scroll down to the macOS download link.
    3. Download arm-performance-libraries_24.04_macOS.tgz.
  3. Unpack ArmPL 24.04.
    1. Double-click the download to uncompress the tgz. NOTE: MacOS may automatically uncompress it in Downloads folder as it downloads, leaving a fresh .tar file. If that is the case, skip this step.
    2. Double-click the .tar file to mount the dmg.
  4. Install ArmPL 24.04.
    1. Navigate into the dmg and then copy the contents to “Downloads”.
    2. In Terminal, run this command:   
      ~/Downloads/armpl_24.04_flang-new_clang_18_install.sh --install_dir=~/Downloads -y
    3. This creates two new directories in the Downloads folder.
  5. Drop the new libraries into IDL 9.0.
    1. In Finder, navigate to ~/Downloads/armpl_24.04_flang-new_clang_18/lib.
    2. Select the following five files:
      • libarmpl_lp64.dylib
      • libarmpl.dylib
      • libarmpl_lp64_mp.dylib
      • libarmpl_mp.dylib
      • libomp.dylib
    3. Copy and paste those files (doing full replacement if prompted) to <idl-dir>/bin/bin.darwin.arm64.
  6. Launch IDL 9.0 and it will be utilizing the updated ArmPL.
  7. If you detect any issues with IDL following this change,  you can always revert to the backed up ArmPL files or just simply reinstall IDL 9.0 fresh to return to the default installation.




Created by BC-US 5/6/2024 | Review by XX XX/XX/XXXX