PGI (Portland Group Inc.) is a compiler suite commonly used for optimizing and compiling C++ and Fortran programs. This compiler suite provides several compiler-specific extensions that can be leveraged to improve the performance and functionality of your code. In this blog post, we will explore some of the PGI C++ compiler-specific extensions and how they can be used in your projects.

#pragma directives

The PGI C++ compiler supports various #pragma directives that allow you to control the optimization and behavior of your code. These directives are specific to the PGI compiler and may not be available in other compilers.

1. #pragma acc

The #pragma acc directive enables OpenACC directives within your code, which can then be used to offload computations to accelerators like GPUs. OpenACC is a parallel programming model designed for heterogeneous computing systems. With PGI compiler’s support for #pragma acc, you can take advantage of GPUs to speed up your computations and improve performance.

Here’s an example of how to use #pragma acc to parallelize a loop using OpenACC:

#pragma acc parallel loop
for(int i = 0; i < N; i++){
    // Compute-intensive task
}

#pragma acc parallel loop

This directive tells the compiler to parallelize the loop using OpenACC. The loop is divided among multiple threads or GPUs, allowing for parallel execution.

2. #pragma ivdep

The #pragma ivdep directive instructs the compiler to ignore vector dependencies and generates vectorized code. This directive can improve the performance of loops by allowing the compiler to apply loop optimizations that would otherwise be inhibited by potential dependencies.

Here’s an example of how to use #pragma ivdep to enable vectorization of a loop:

#pragma ivdep
for(int i = 0; i < N; i++){
    // Vectorizable operations
}

#pragma ivdep

This directive informs the compiler to ignore possible dependencies in the loop and vectorize it as much as possible, potentially leading to better performance.

Conclusion

The PGI C++ compiler provides several useful extensions through #pragma directives. By leveraging these compiler-specific extensions, you can bring performance improvements and take advantage of advanced features such as parallelization and vectorization. However, it’s important to note that these extensions are specific to the PGI compiler and may not be supported by other compilers. Make sure to check the documentation and compatibility before using them in your code.

#PGI #C++ #compiler #extensions #programming