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Table of Contents
Compiling Tips and Tricks
A technique is what you call any trick you use more than once.
Compilers
The three main compiled languages for HPC are C, Fortran and C++.
Many people write the first and last as C/C++. That's wrong. C and C++ are different languages. Confusing them is responsible for many problems.
The compilers found at the CHPC fall into three families: gcc, Intel and Sun Studio.
There's a fourth family, IBM XL, but we won't worry about it since the P690s are gone and BG/P is DOA.
Table of Compilers
| Language | GCC | Intel |
|---|---|---|
| C | gcc | icc |
| Fortran | gfortran | ifort |
| C++ | g++ | icpc |
By convention, there are variables that define the actual command invoked (see above) and which can be used in the shell, with make files and configure.
Table of Compiler Variables
| Variable | Compiler | Example |
|---|---|---|
CC | C | CC=gcc |
FC | Fortran | FC=ifort |
CXX | C++ | CXX=/opt/gridware/intel/comp12/composerxe-2011.0.084/bin/intel64/icpc |
The last example shows that you can include the full path to a particular compiler.
Fortran comes in two main flavours, Fortran 77 and Fortran 90 (also called 9x since it includes Fortran 95). By default FC refers to the Fortran 9x compiler and when it is necessary to also point to a Fortran 77 compiler:
F77 | Fortran 77 | F77=g77 |
|---|
Example
When building an MPI library — for example, OpenMPI — one would specify all four since MPI provides MPI compilers for:
mpicc | MPI C compiler |
mpicxx | MPI C++ compiler |
mpif77 | MPI Fortran 77 compiler |
mpif90 | MPI Fortran 90 compiler |
Before the usual make; make install tell configure which compilers to use:
./configure --prefix=$HOME/mpi/intel/ \ CC=icc CXX=icpc F77=ifort FC=ifort \ --with-openib \ --with-openib-libdir=/usr/lib64/
The above example uses Intel compilers and also builds in InfiniBand support.
