cpeCray toolchain¶

NOTE: Stuff in italics has to be checked: Do these options really work?

Note about the compilers¶

The major version of the cce module corresponds to the major version of the clang/LLVM compilers on which it is based for all versions that are relevant for LUMI.

Available options¶

The cpeCray toolchain supports the common toolchain options, and some additional Cray-specific flags, two of which are really just redefinitions of standard compiler flags.

Compiler flags that are inherited from the LLVM compilers on which the compilers are based¶

Option	Categorie	What?
lto	code generation	Enable Link Time Optimization (in the default 'full' mode)
offload-lto	code generation	Enable LTO for offload compilation (in the default 'full' mode)

These options should not be used in projects that also contains Fortran code.

cpeCray-specific flags¶

Option	Categorie	What?
dynamic	code generation	Generate dynamically linked executable (default: True)
mpich-mt	parallelism	Alternate Cray-MPICH library for MT support (default: False)

mpich-mt: Directs the driver to link in an alternate version of the Cray-MPICH library which provides fine-grained multi-threading support to applications that perform MPI operations within threaded regions. (default: False)

Two further options trigger different compiler flags than in the GCC toolchain: verbose and optarch but have otherwise the same meaning.

Mapping of options onto compiler flags¶

Some Cray-specific remarks¶

A number of options are different for the clang-based C/C++ compilers and Fortran compiler, something that EasyBuild cannot easily deal with. This is, e.g., the case for the options that set the floating point computation model, so for now these are left blank.
- Fortran floating point optimisation and accuracy options: -hfp0 to -hfp4, with -hfp2 the default according to the manual.
  
  The manual only claims -hfp0 to -hfp3.
- For OpenMP the manual also claims a different option for the Fortran compiler, but it turns out that recent versions also support -fopenmp so no changes are needed with respect to the standard EasyBuild behaviour.
  
  The manual claims that there is also a -fnoopenmp but that turns out to be wrong in cce 12.
The situation about promoting integer and real in Fortran to 8 bytes is very confusing. Those options are not properly documented in the manuals. The Cray driver manual only mentions -default64 which according to the documentation is then converted to -sdefault64. In the documentation, there is mention of -sreal64 (or -s real64`), but this option is nowhere to be found in the list of compiler options. However, it turns out that-sinteger64(or-s integer64) and-sreal64(or-s real64``) both exist and do what is expected from them.

TODO: Check if -flto exist in Fortran and C and if so, add to the options.

Compiler optimization level¶

The common options translate into:

Option	Flag
noopt	-O0
lowopt	-O1
defaultopt	-O2
opt	-O3

Other optimization-related options (and see also parallelism below):

Option	Flag
unroll	-funroll
optarch	TODO

Floating point precision¶

These flags are currently not correctly honoured.

Option	Flag
strict	/
precise	/
defaultprec	/
loose	/
veryloose	/

Other floating-point optimisation and accuracy-related flags:

Option	What?
ieee	/

Option	Flag
vectorize	/
openmp	-fopenmp
usempi	No compiler flags
mpich-mt	-craympich-mt

Code generation and linking options¶

Option	Flag
dynamic	No flag as this is currently the only mode supported
32bit	-m32
debug	-g
pic	-fPIC
packed-linker-options	Pack the linker options as comma separated list (default: False)
shared	-shared
static	-static
rpath	Use RPATH wrappers when --rpath is enabled in EasyBuild configuration (default: True)

Option	Flag
cstd	-std=%(value)s
i8	-sinteger64
r8	-sreal64

Miscellaneous options¶

Option	Flag
verbose	-craype-verbose