.TH opalcc 1 "OPEN MPI TOOLS" "OPEN MPI" "OPEN MPI TOOLS"
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.SH NAME
This man page describes the wrapper compilers for the Open MPI (OMPI),
OpenRTE (ORTE), and Open Portable Access Layer (OPAL):
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.PP
mpicc, mpiCC / mpic++, mpif77, mpif90
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.PP
ortecc, orteCC / ortec++
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.PP
opalcc, opalCC / opalc++
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.SH SYNTAX
mpicc [-showme|-showme:compile|-showme:link] ...
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.PP
The same syntax works for all the wrapper compilers; \fImpicc\fR is
shown above as a single example representing all the others.
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.SH OPTIONS
.TP
-showme 
Do not invoke the underlying compiler.  Instead, show the command line
that would be executed to compile the program.  \fBNOTE:\fR If a
non-filename argument is passed on the command line, the \fI-showme\fR
option will \fInot\fR display any additional flags.  For example, both
"mpicc --showme" and "mpicc --showme my_source.c" will show all the
wrapper-supplied flags.  But "mpicc -showme -v" will only show the
underlying compiler name and "-v".
.TP
-showme:compile
Do not invoke the underlying C/C++ compiler.  Instead, show the
compiler flags that would be supplied to the C/C++ compiler.
.TP
-showme:link
Do not invoke the underlying C/C++ compiler.  Instead, show the linker
flags that would be supplied to the C/C++ compiler.
.PP
See cc(1) and CC(1) (or whatever your underlying C/C++ compilers are)
for all other options.
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.SH DESCRIPTION
.PP
Conceptually, the role of these commands is quite simple:
transparently add relevant compiler and linker flags to the user's
command line that are necessary to compile / link OPAL, ORTE, and OMPI
programs, and then invoke the underlying compiler to actually perform
the command.
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.PP
As such, these commands are frequently referred to as "wrapper"
compilers because they do not actually compile or link applications
themselves; they only add in command line flags and invoke the
back-end compiler.
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.SS Background
Open MPI is comprised of three software layers: OPAL (Open Portable
Access Layer), ORTE (Open Run-Time Environment), and OMPI (Open MPI).
There are wrapper compilers for each layer; each layer's wrapper only
links in the libraries relevant for that layer.  Specifically, each
layer provides the following wrapper compilers:
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.TP 4
OPAL
\fIopalcc\fR, \fIopalc++\fR, \fIopalCC\fR (only on systems with
case-sensitive filesystems)
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.TP
ORTE
\fIortecc\fR, \fIortec++\fR, \fIorteCC\fR (only on systems with
case-senstive filesystems)
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.TP
OMPI
\fImpicc\fR, \fImpic++\fR, \fImpiCC\fR (only on systems with
case-senstive file systems), \fImpif77\fR, \fImpif90\fR
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.PP
Some systems may not have all the wrapper compilers listed above
depending on which back-end compilers are available.  For example, if
a system does not have any Fortran compilers available, \fImpif77\fR
and \fImpif90\fR will not be available.
.PP
The descriptions below are use the names of the MPI wrapper compilers,
but generally apply to all wrapper compilers.  Likewise, the name
\fImpiCC\fR is used in the descriptions below; it is only available on
systems with a C++ compiler and case-sensitive filesystems
(\fImpic++\fR is available on all systems with a C++ compiler).
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.SS Overview
\fImpicc\fR and \fImpiCC\fR (\fImpic++\fR is a synonym for \fImpiCC\fR
provided for filenames that do not support case-sensitive filenames)
are convenience wrappers for the underlying C and C++ compilers.
Likewise, \fImpif77\fR and \fImpif90\fR are convenience wrappers for
the underlying F77 and F90 compilers.  Translation of an Open MPI
program requires the linkage of the Open MPI-specific libraries which
may not reside in one of the standard search directories of ld(1).  It
also often requires the inclusion of header files what may also not be
found in a standard location.  
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.PP
\fImpicc\fR passes its arguments to the underlying C compiler along
with the -I, -L and -l options required by Open MPI programs.
Likewise, \fImpiCC\fR (\fImpic++\fR), \fImpif77\FR, and \fImpif90\fR
are similar, but invoke the underlying C++, F77, and F90 compiler
instead, respectively.
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.PP
The Open MPI Team \fIstrongly\fR encourages using the wrapper
compilers instead of attempting to link to the Open MPI libraries
manually.  This allows the specific implementation of Open MPI to
change without forcing changes to linker directives in users'
Makefiles.  Indeed, the specific set of flags and libraries used by
the wrapper compilers depends on how Open MPI was configured and
built; the values can change between different installations of the
same version of Open MPI.
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.PP
Indeed, since the wrappers are simply thin shells on top of an
underlying compiler, there are very, very few compelling reasons
\fInot\fR to use \fImpicc\fR / \fImpiCC\fR.  When it is not possible
to use the wrappers directly, the \fI-showme:compile\fR and
\fI-showme:link\fR options should be used to determine what flags the
wrappers would have used.  For example:
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.PP
shell$ cc -c file1.c `mpicc -showme:compile`
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.PP
shell$ cc -c file2.c `mpicc -showme:compile`
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.PP
shell$ cc file1.o file2.o `mpicc -showme:link` -o my_mpi_program
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.SH NOTES
.PP
It is possible to make the wrapper compilers multi-lib aware.  That
is, the libraries and includes specified may differ based on the
compiler flags specified (for example, with the GNU compilers on
Linux, a different library path may be used if -m32 is seen versus
-m64 being seen).  This is not the default behavior in a standard
build, but can be activated (for example, in a binary package
providing both 32 and 64 bit support).  More information can be found
at:
.PP
  https://svn.open-mpi.org/trac/ompi/wiki/compilerwrapper3264
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.SH FILES
.PP
The string that the wrapper compilers insert into the command line
before invoking the underlying compiler are stored in a text file
created by Open MPI and installed to
\fI$pkgdata/<wrapper_name>-wrapper-data.txt\fR, where \fI$pkgdata\fR
is typically \fI$prefix/share/openmpi\fR, and \fI$prefix\fR is the top
installation directory of Open MPI.  \fI<wrapper_name>\fR is the
executable name of the wrapper compiler, such as \fImpicc\fR and
\fImpic++\fR.
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.PP
It is rarely necessary to edit this file, but it can be examined to
gain insight into what flags the wrappers are placing on the command
line.
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.SH ENVIRONMENT VARIABLES
.PP 
By default, the wrappers use the compilers that were selected when
Open MPI was configured.  These compilers were either found
automatically by Open MPI's "configure" script, or were selected by
the user in the CC, CXX, F77, and/or FC environment variables 
before "configure" was invoked.  Additionally, other arguments
specific to the compiler may have been selected by configure.
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.PP
These values can be selectively overridden by either editing the text
files containing this configuration information (see the \fBFILES\fR
section), or by setting selected environment variables of the
form "project_value".
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.PP
Valid project names are \fIOPAL\fR, \fIORTE\fR, and \fIOMPI\fR.  Valid
value names are:
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.TP
CC
C compiler
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.TP
CFLAGS
C compiler flags
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.TP
CXX
C++ compiler
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.TP
CXXFLAGS
C++ compiler flags
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.TP
F77
Fortran 77 compiler
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.TP
FFLAGS
Fortran 77 compiler flags
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.TP
FC
Fortran 90 compiler
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.TP
FCFLAGS
Fortran 90 compiler flags