Recommended compiler options

The PALM code uses standard FORTRAN 2003 and should compile on any compiler conforming with this standard. For known issues with current compilers see Help/FAQ.

Compilers currently used by the PALM group are Intel, Cray, PGI and GNU-Fortran. We recommend to use these compilers with the following options (library and include-file options are omitted here):

Intel (version 14 and higher) for optimized code:

ifort -fpp -fpe0 -O3 -xHost -fp-model source -ftz -no-prec-div -no-prec-sqrt -ip

Option	meaning
-fpp	Runs the Fortran preprocessor on source files before compilation.
-fpe0	Specifies the floating-point exception handling level. Floating-point invalid, divide-by-zero, and overflow exceptions are enabled. If any such exceptions occur, execution is aborted. This option causes denormalized floating-point results to be set to zero.
-O3	Performs O2 optimizations and enables more aggressive loop transformations such as Fusion, Block-Unroll-and-Jam, and collapsing IF statements.
-xHost	This option tells the compiler to generate instructions for the highest instruction set available on the compilation host processor.
-fp-model source	Controls the semantics of floating-point calculations. Rounds intermediate results to source-defined precision. This option is required to force jobs to deliver reproduceble results. If not set, two PALM runs with exactly identical setup may produce different results. Code performance is slightly reduced when using this option.
-ftz	This option flushes denormal results to zero when the application is in the gradual underflow mode. It may improve performance if the denormal values are not critical to your application's behavior.
-no-prec-div	Enables optimizations that give slightly less precise results than full IEEE division.
-no-prec-sqrt	The compiler uses a faster but less precise implementation of square root.
-ip	Enables additional interprocedural optimizations for single-file compilation.

Intel (version 14 and higher) for debugging:

ifort -fpp -fpe0 -O0 -check -check nooutput_conversion -traceback -g

Option	meaning
-O0	Disables all optimizations.
-check	All available runtime checks (e.g. array bounds) are switched on.
-check nooutput_conversion	No checking for the fit of data items within a designated format descriptor field. If this option isn't set, compilation aborts with errors.
-traceback	Tells the compiler to generate extra information in the object file to provide source file traceback information when a severe error occurs at run time.
-g	Tells the compiler to generate full debugging information in the object file.

Cray (version 8.5.6):

ftn -eZ -em -O3 -hnoomp -hnoacc -hfp3 -hdynamic -dynamic

Option	meaning
-eZ	Perform source preprocessing and compilation on Fortran source files.
-em	When this option is enabled, the compiler creates .mod files to hold module information for future compiles.
-O3	Switch on most aggressive optimization level.
-hnoomp	Disable compiler recognition of OpenMP directives.
-hnoacc	Disables the compiler recognition of OpenACC accelerator directives.
-hfp3	Controls the level of floating point optimizations. (highest level would be -hfp4)
-hdynamic -dynamik	Directs the compiler driver to link dynamic libraries at runtime.

Cray (version 8.5.6) for debugging:

ftn -eZ -K trap=fp -eD -ei -em -O0 -hnoomp -hnoacc -hdynamic -dynamic

Option	meaning
-K trap=fp	Enable traps on divz, inv, or ovf exceptions.
-eD	Enables all debugging options.
-ei	Initializes all undefined local stack, static, and heap variables of type REAL or COMPLEX to an invalid value (signaling NaN).
-O0	Disables all optimizations including floating point optimizations and OpenACC acceleration.

Important on Cray-systems: Getting tracebacks requires setting of export ATP_ENABLED=1 before execution of PALM. Use an input command in the configuration file for that:

IC:export ATP_ENABLED=1

GNU Fortran:

gfortran -Ofast

Option	meaning
-Ofast	Disregard strict standards compliance. -Ofast enables all -O3 optimizations. It also enables optimizations that are not valid for all standard-compliant programs. It turns on -ffast-math and the Fortran-specific -fstack-arrays, unless -fmax-stack-var-size is specified, and -fno-protect-parens.

GNU Fortran for debugging:

gfortran -O0 -g -ffpe-trap=invalid,zero,overflow -Wall -Wextra -pedantic -fcheck=all -fbacktrace

Option	meaning
-O0	Reduce compilation time and make debugging produce the expected results.
-g	Produce debugging information in the operating system's native format.
-ffpe-trap=	Specifies a list of IEEE exceptions when a Floating Point Execption (FPE) should be raised. invalid: invalid floating point operation, such as SQRT(-1.0), zero: division by zero, overflow: overflow in a floating point operation.
-Wall	Enables commonly used warning options pertaining to usage that we recommend avoiding and that we believe are easy to avoid. This currently includes -Waliasing, -Wampersand, -Wsurprising, -Wintrinsics-std, -Wno-tabs, -Wintrinsic-shadow and -Wline-truncation.
-Wextra	Enables some warning options for usages of language features which may be problematic. This currently includes -Wcompare-reals and -Wunused-parameter.
-pedantic	Issue warnings for uses of extensions to Fortran 95.
-fcheck=all	Enable all run-time tests of -fcheck.
-fbacktrace	Specify that, when a runtime error is encountered or a deadly signal is emitted (segmentation fault, illegal instruction, bus error or floating-point exception), the Fortran runtime library should output a backtrace of the error.

Importrant: Older versions of the GNU compiler (4.8.X and older) do not support (or have problems with) some functions from the C-interface that are used in PALM. See also our FAQ page.