declare_variant_if

Declare Variant with Conditional Target Offload Example

This example demonstrates the following:

1. You must set -fopenmp-version=50 for OpenMP 5.0 functionality.
2. How to use the if clause in pragmas for conditional target offload.
3. How to use function variants for different architectures.

Example Description

The example implements the SAXPY (Single-Precision A·X Plus Y) operation using OpenMP. It demonstrates:

• Conditional offloading using the if clause in #pragma omp target.
• Architecture-specific function variants using #pragma omp declare variant.

The base saxpy function runs on the host, while architecture-specific variants (amdgcn_saxpy and nvptx_saxpy) are executed on AMD and NVIDIA GPUs, respectively.

Build Instructions

To build the example, run the following command:

make

Ensure that the LLVM_GPU_ARCH environment variable is set to the appropriate GPU architecture (e.g., gfx90a for AMD GPUs or sm_70 for NVIDIA GPUs).

Execution Instructions

To execute the example, run:

make run

Expected Output

The output will vary depending on the target architecture and the value of the if clause in the #pragma omp target directive. A typical output might look like:

Calling saxpy with high threshold for device execution
saxpy: Running on host. IsHost:1
Calling saxpy with low threshold for device execution
amdgcn_saxpy: Running on amdgcn device. IsHost:0
y[0],y[N-1]:     5   640