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We highly recommend to try as much different compilers as possible and compare the performance of the generated code! If you code according to language standards, this is almost for free but can give you a significant speedup! There is no such thing as an "ideal" compiler! One suites better to application A, one suites better to application B (cf. Best Practice Guide AMD EPYC (Naples)).
Please note that compilers do not use optimization flags by default at the moment. Hence, please refer to Compiler Options Quick Reference Guide and set the respective flags on your own (with znver1 for Naples and znver2 for Rome nodes). Compiler Usage Guidelines for AMD64 Platforms might also be a source of inspiration w.r.t. optimization flags.
Make sure to load a more up to date version of the GNU Compiler Collection than the one preinstalled in the system
module load compiler/gnu/9.1.0
Then compile with
AOCC is the AMD Optimizing C/C++ Compiler based on LLVM. It contains a Fortran compiler (flang) as well.
Load aocc module
module load compiler/aocc/2.0.0
and do not use
since the latter might give very bad performance!
With respect to PGI, we recommend to use
<compiler> -tp=zen -O3
Compiler Options for High Performance Computing
This section shows compiler flags for GNU-compatible compilers (gnu, aocc, intel), other compilers may have other options for the described functionality.
Large jobs with thousands of processes can overload the file systems connected to the cluster during startup if the binary is linked to (many) shared libraries that are stored on these file systems.
To avoid this issue and to also improve the performance by reducing the overhead from function calls from shared libraries, compiling dependencies statically is recommended.
During link-time, you can set the compiler to prefer static libraries over shared libraries if both are found in the library search path with
# Link libhdf5 statically, set back to look for shared libraries again after (default) <compiler> ... -Wl,-Bstatic -lhdf5 -Wl,-Bdynamic
You can also specify a static library filename in the library search path directly
# Staticaclly link libhdf5.a <compiler> ... -l:libhdf5.a
Or provide the full path to the static library like with other object files
# Staticaclly link libhdf5.a <compiler> ... /path/to/static/lib/libhdf5.a
Keep in mind that all the symbols referenced in the static library need to be resolved during linking. Thus, linking to additional (static) libraries may be required.
Link-Time Optimization (LTO)
This technique allows the compiler to optimize the code at link time. During this, further rearrangement of the code from separate object files is performed.
The option needs to be set at compile time and link time:
# Compile with LTO in mind <compiler> -flto -o component1.o -c component1.c <compiler> -flto -o component2.o -c component2.c # Link with LTO <compiler> -flto -o program component1.o component2.o
Keep in mind LLVM(AOCC) compiles LLVM bitcode files instead of ELF object files when using LTO. Using tools like objdump, readelf, strip, etc. on these files won't work.
More information here: https://www.llvm.org/docs/LinkTimeOptimization.html
Profile Guided Optimization (PGO)
This optimization can lead to a 10-20% boost in performance in some cases. It basically collects information about how the program actually runs and improves the assumptions made about which code paths are more likely to be taken.
This requires the code to be compiled twice and the program being run with a representative use-case in-between.
A good example for GCC can be found here:
PGO documentation for LLVM:
PGO documentation for the Intel Compiler: