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{{DISPLAYTITLE:Compilers — Magus02 HPC}}
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📍 [[Magus02/Knowledge_Base|Magus02 Knowledge Base]] → HPC User → Compilers
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A compiler translates human-readable source code (C, C++, Fortran) into executable binary programs. Choosing the right compiler and flags can significantly affect application performance on Magus02.

__TOC__

== General ==

Compilers are loaded via the [[Magus02/Modules|module system]]. Never invoke compilers directly without loading the appropriate module first.

A basic compilation workflow:

<pre>
# 1. Load the compiler module
$ module load intel/oneapi

# 2. Compile your source code
$ icc hello_world.c -o hello_world

# 3. Run the resulting binary
$ ./hello_world
Hello, World!
</pre>

=== Optimization Flags ===

Always compile with optimization enabled for production runs. Common optimization levels:

{| class="wikitable" style="width:100%;"
|-
! Flag !! Effect
|-
| <code>-O0</code> || No optimization. Fastest compile; use when debugging.
|-
| <code>-O1</code> || Basic optimizations.
|-
| <code>-O2</code> || Recommended default for production — good balance of speed and compile time.
|-
| <code>-O3</code> || Aggressive optimization, including vectorization. May change floating-point behavior.
|-
| <code>-march=native</code> || Optimize specifically for the current CPU architecture (AMD EPYC / Intel Xeon on Magus02).
|}

== Intel Compiler (icc / ifort) ==

The Intel compiler is optimized for Intel and compatible AMD microprocessors and often produces the fastest binaries for numerical codes.

Load the module:
<pre>
$ module load intel/oneapi
</pre>

Compile C, C++, or Fortran:
<pre>
$ icc source.c -O2 -o my_program # C
$ icpc source.cpp -O2 -o my_program # C++
$ ifort source.f90 -O2 -o my_program # Fortran 90
</pre>

== GNU Compiler Collection (gcc / gfortran) ==

GCC is a free, open-source compiler available on all platforms. Reliable and widely tested.

Load the module:
<pre>
$ module load gcc/11.2.0
</pre>

Compile:
<pre>
$ gcc source.c -O2 -o my_program # C
$ g++ source.cpp -O2 -o my_program # C++
$ gfortran source.f90 -O2 -o my_program # Fortran
</pre>

== LLVM / Clang ==

The LLVM project provides modern, modular compiler infrastructure. Useful for C/C++ and when targeting specific optimization analyses.

<pre>
$ module load llvm
$ clang source.c -O2 -o my_program # C
$ clang++ source.cpp -O2 -o my_program # C++
</pre>

== PGI / NVIDIA Compilers ==

PGI compilers (now NVIDIA HPC SDK) are particularly useful for GPU programming with OpenACC pragmas.

<pre>
$ module load nvhpc
$ pgcc source.c -O2 -o my_program
$ pgfort source.f90 -O2 -o my_program
</pre>

== Compiling Multi-file Projects ==

For programs split across multiple source files, use a linker or a build system:

<pre>
# Compile with multiple source files:
$ icc file1.c file2.c file3.c -O2 -o my_program

# Or use make (for larger projects with a Makefile):
$ module load intel/oneapi
$ make
</pre>

== References ==

* [https://software.intel.com/en-us/intel-compilers Intel Compilers]
* [https://gcc.gnu.org GNU Compiler Collection]
* [https://llvm.org LLVM Compiler Infrastructure]
* [[Magus02/MPI_Usage|MPI Usage — Compiler Wrappers]]
* [[Magus02/OpenMP_Usage|OpenMP Usage — Compiler Flags]]

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