OpenMP Command-Line Argument Reference

Welcome to the OpenMP in LLVM command line argument reference. The content is not a complete list of arguments but includes the essential command-line arguments you may need when compiling and linking OpenMP. Section OpenMP Command-Line Arguments lists OpenMP command line options for multicore programming while Offloading Specific Command-Line Arguments lists options relevant to OpenMP target offloading.

OpenMP Command-Line Arguments


Enable the OpenMP compilation toolchain. The compiler will parse OpenMP compiler directives and generate parallel code.


Enable all Clang extensions for OpenMP directives and clauses. A list of current extensions and their implementation status can be found on the support page.


This option enables OpenMP only for single instruction, multiple data (SIMD) constructs.


Use the static OpenMP host runtime while linking.


Set the OpenMP version to a specific version <arg> of the OpenMP standard. For example, you may use -fopenmp-version=45 to select version 4.5 of the OpenMP standard. The default value is -fopenmp-version=51 for Clang.

Offloading Specific Command-Line Arguments


Specify which OpenMP offloading targets should be supported. For example, you may specify -fopenmp-targets=amdgcn-amd-amdhsa,nvptx64. This option is often optional when --offload-arch is provided.
It is also possible to offload to CPU architectures, for instance with -fopenmp-targets=x86_64-pc-linux-gnu.


Specify the device architecture for OpenMP offloading. For instance --offload-arch=sm_80 to target an Nvidia Tesla A100, --offload-arch=gfx90a to target an AMD Instinct MI250X, or --offload-arch=sm_80,gfx90a to target both.
It is also possible to specify -fopenmp-targets without specifying --offload-arch. In that case, the executables amdgpu-arch or nvptx-arch will be executed as part of the compiler driver to detect the device architecture automatically.
Finally, the device architecture will also be automatically inferred with --offload-arch=native.


Compile only the code that goes on the device. This option is mainly for debugging purposes. It is primarily used for inspecting the intermediate representation (IR) output when compiling for the device. It may also be used if device-only runtimes are created.


Compile only the code that goes on the host. With this option enabled, the .llvm.offloading section with embedded device code will not be included in the intermediate representation.


Compile the target regions for both the host and the device. That is the default option.

-Xopenmp-target <arg>

Pass an argument <arg> to the offloading toolchain, for instance -Xopenmp-target -march=sm_80.

-Xopenmp-target=<triple> <arg>

Pass an argument <arg> to the offloading toolchain for the target <triple>. That is especially useful when an argument must differ for each triple. For instance -Xopenmp-target=nvptx64 --offload-arch=sm_80 -Xopenmp-target=amdgcn --offload-arch=gfx90a to specify the device architecture. Alternatively, -Xarch_host <arg> and -Xarch_device <arg> can pass an argument to the host and device compilation toolchain.

-Xoffload-linker<triple> <arg>

Pass an argument <arg> to the offloading linker for the target specified in <triple>.

-Xarch_device <arg>

Pass an argument <arg> to the device compilation toolchain.

-Xarch_host <arg>

Pass an argument <arg> to the host compilation toolchain.


Enable device link time optimization (LTO) and select the LTO mode <arg>. Select either -foffload-lto=thin or -foffload-lto=full. Thin LTO takes less time while still achieving some performance gains. If no argument is set, this option defaults to -foffload-lto=full.


This option is set to avoid generating the host fallback code executed when offloading to the device fails. That is helpful when the target contains code that cannot be compiled for the host, for instance, if it contains unguarded device intrinsics.
This option can also be used to reduce compile time.
This option should not be used when one wants to verify that the code is being offloaded to the device. Instead, set the environment variable OMP_TARGET_OFFLOAD='MANDATORY' to confirm that the code is being offloaded to the device.


Enable debugging in the device runtime library (RTL). Note that it is both necessary to configure the debugging in the device runtime at compile-time with -fopenmp-target-debug=<arg> and enable debugging at runtime with the environment variable LIBOMPTARGET_DEVICE_RTL_DEBUG=<arg>. Further, it is currently only supported for Nvidia targets as of July 2023. Alternatively, the environment variable LIBOMPTARGET_DEBUG can be set to debug both Nvidia and AMD GPU targets. For more information, see the debugging instructions. The debugging instructions list the supported debugging arguments.


Emit code that is Just-in-Time (JIT) compiled for OpenMP offloading. Embed LLVM-IR for the device code in the object files rather than binary code for the respective target. At runtime, the LLVM-IR is optimized again and compiled for the target device. The optimization level can be set at runtime with LIBOMPTARGET_JIT_OPT_LEVEL, for instance, LIBOMPTARGET_JIT_OPT_LEVEL=3 corresponding to optimizations level -O3. See the OpenMP JIT details for instructions on extracting the embedded device code before or after the JIT and more.
We want to emphasize that JIT for OpenMP offloading is good for debugging as the target IR can be extracted, modified, and injected at runtime.


In upstream LLVM, OpenMP only uses the new driver. However, enabling this option for experimental linking with CUDA or HIP files is necessary.


Do not link the device library for CUDA or HIP device compilation.


Do not include the default CUDA or HIP headers, and do not add CUDA or HIP include paths.