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Cray Fortran

Contents

• Introduction
• Options
• Documentation

Introduction

The Fortran compiler on Phoenix is Cray Fortran. It supports the Fortran 95 standard and some features expected Fortran 2000. Unlike other Fortran compilers that have multiple commands (e.g. "f77", "f90", etc.), the Cray compiler has only one command.

ftn ...

MPI include files and libraries are available by default. No additional options are required to compile or link MPI codes.

Options

The following options control how source files are translated into machine code.

-f fixed	The source code uses fixed-form syntax, like in Fortran 77. This option is on by default for source files ending in ".f", ".F", ".f77", and ".F77".
-f free	The source code uses free-form syntax, introduced in Fortran 90. This option is on by default for source files ending in ".f90", ".F90", ".ftn", and ".FTN".
-F	Enable preprocessor macros to be expanded throughout the file. By default, macros are only expanded on lines with preprocessor directives (lines starting with "#").
-s default64	Make the default size of variables the same as for previous generations of Cray systems, 8 bytes for all but "DOUBLE PRECISION". Without this option, the default size of these variables is 4 bytes, like on most non-Cray systems.

The following options control the amount of debugging information generated by the compiler. They can adversely affect optimization.

-g	Full debugging. Turns off optimization.
-G1	Block-level debugging. Limits optimization.
-G2	Post-mortem (core file) debugging. Allows most optimization.

For most cases, the default levels of optimization are appropriate. Here are a few exceptions.

-rm	Generate a "loopmark" listing. The listing appears in a file with the suffix ".lst". Loopmarks illustrate where optimization did and did not occur, and why.
-Omodinline	Allow procedures in modules to be inlined into procedures that use those modules. Inlining can be critical for vectorization.
-Ogen_private_callee	Generate the code necessary to call each procedure from within a stream. With this option, the procedures may be called as usual or from within a multi-streamed region.
-Otask0	This option insures that the compiler does not try to use OpenMP parallelism. This option is good for safety.
-Z	Compile Co-Array Fortran.

On many systems, you must specify compiler options to create an executable that provides profiling data. On the Cray X1, you instead instrument an existing executabl using the "pat_build" tool.

pat_build old_executable instrumented_executable

You then run the instrumented executable, which produces a ".xf" file. Use "pat_report" to generate a profile.

pat_report file.xf

See "man pat_build" and "man pat_report" for more information on the types of profiles you can produce.

Documentation

See "man ftn" for a full list of compiler options. PDF and HTML documentation is also available online from Cray at the following URL.

http://www.cray.com/craydoc/

In particular, see the following documents.

• Optimizing Applications on the Cray X1 System
• Fortran Language Reference Manual, Volume 1
• Fortran Language Reference Manual, Volume 2
• Fortran Language Reference Manual, Volume 3
• Cray Fortran Compiler Commands and Directives Reference Manual