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cpeAOCC toolchain

Note: The options are for the file included in this repository and are not the same as those for the repository at CSCS.

Note about the compilers

From the user guides, introduction section:

  • AOCC 2.1 is based on LLVM 9.0 release (, 19th Sep 2019) with improved Flang Fortran frond-end added with F2008 features and bug fixes.
  • AOCC 2.2 is based on LLVM 10.0 release (, 24th Mar 2020) with improved Flang Fortran front-end added with F2008 features and bug fixes.
  • AOCC 3.0 is based on LLVM 12 trunk (, 22nd Oct 2020) with Flang as a Fortran front-end added with F2008, Real 128 features. AOCC 3.0 also includes the support for OpenMP Debugging Interface (OMPD) APIs.
  • AOCC 3.1 release is based on LLVM 12 release (, 14th April 2021) with Flang as a Fortran front-end added with F2008 and Real 128 features. It is an incremental version of AOCC 3.0 that includes bug fixes and a support for compiler directives in Flang.
  • AOCC 3.2 AOCC 3.2 is based on the LLVMTM 13 compiler infrastructure (, 4 October 2021) and includes bug fixes and support for other new features.

Available options

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

AOCC-specific flags

The following options map on AOCC-dpecific compiler flags can be similar to similar options in the cpeGNU toolchain:

Option Categorie What?
lto code generation Enable Link Time Optimization

cpeAOCC-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

Compiler optimization level

The common options translate into:

Option Flag
noopt -O0
lowopt -O1
defaultopt -O2 -fvectorize -fslp-vectorize
opt -O3

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

Option Flag
unroll -funroll-loops
optarch TODO

Floating point precision

The decision of our mapping is based partly on information from Cray and partly on looking through various manuals on Clang.

  • Level strict: We simply stick to -ffp-model=strict. This automatically disables all of the -ffast-math enablements so there is no need to add -fno-fast-math. Note that at this level, fused multiply adds are disabled.
  • Level precise: We stick to -ffp-model=precise and add -ffp-contract=fast-honor-pragmas.
  • Default level: Currently the same as strict.
  • Level loose: Set to -ffp-model=fast but try to turn on again a few safeguards: -ffp-contract=fast-honor-pragmas, -fhonor-infinities, -fhonor-nans, -fsigned-zeros.
  • Level veryloose: Set to -ffp-model=fast

Note: Very recnet versions of clang add -ffp-contract=fast-honor-pragmas which may be interesting to add to precise, defaultprec and loose but is not yet supported by AOCC 2.2.

Option Flag
strict -ffp-model=strict
precise -ffp-model=precise
defaultprec -ffp-model=precise
loose -ffp-model=fast -fhonor-infinities -fhonor-nans -fsigned-zeros
veryloose -ffp-model=fast

Other floating-point optimisation and accuracy-related flags:

Option What?
ieee Not supported in clang/flang
Option Flag
vectorize False: -fno-vectorize -fno-slp-vectorize
True: -fvectorize -fslp-vectorize
loop -ftree-switch-conversion -floop-interchange -floop-strip-mine -floop-block
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
lto -flto
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 -fdefault-integer-8
r8 -fdefault-real-8
f2c -ff2c

Miscellaneous options

Option Flag
verbose -craype-verbose