Hello Steven,
when using AX_MPI (formerly ACX_MPI (so search bots pick this up)) for
either some or all of the C, C++, and Fortran languages, the macro
documents a way to use it if all of the corresponding sources are to be
treated with the MPI compiler wrapper:
# On success, it sets the MPICC, MPICXX, MPIF77, or MPIFC output variable
# to the name of the MPI compiler, depending upon the current language.
# (This may just be $CC/$CXX/$F77/$FC, but is more often something like
# mpicc/mpiCC/mpif77/mpif90.) It also sets MPILIBS to any libraries that
# are needed for linking MPI (e.g. -lmpi or -lfmpi, if a special
# MPICC/MPICXX/MPIF77/MPIFC was not found).
#
# If you want to compile everything with MPI, you should set:
#
# CC="MPICC" #OR# CXX="MPICXX" #OR# F77="MPIF77" #OR# FC="MPIFC"
(sic typos s/MPI/$&/g by the way)
# LIBS="$MPILIBS $LIBS"
My experience is that this is not quite sufficient, at least when
Automake and/or Libtool are added in the mix; it is unclear who to
attribute the problem to.
The gist of the problem is that with:
AC_INIT([foo], [1.0])
AM_INIT_AUTOMAKE([foreign])
ACX_MPI
CC=$MPICC
# ...
AC_CONFIG_FILES([Makefile])
AC_OUTPUT
ACX_MPI first expands AC_PROG_CC which of course checks for the C
compiler etc. But also, automake attaches dependency tracking checking
to AC_PROG_CC. This means, all those tests done right after AC_PROG_CC
are done with $CC and not with $MPICC. So, when a user does
./configure MPICC=/super/duper/mpicc
and that driver doesn't use, say, the first gcc found in $PATH, all
those test results are problematic.
I've been using something like this as a workaround:
# Do not even look for a non-MPI C compiler if MPICC is set.
if test -z "$CC" && test -n "$MPICC"; then
CC=$MPICC
fi
AX_MPI
CC=$MPICC
LIBS="$MPILIBS $LIBS"
under the assumption that if the user passes both variable, she knows
what she's doing, and when neither are passed, well then, let's hope
gcc/cc and mpicc will somehow be similar.
I'm not sure how a better solution would look like, given that your
AC_CHECK_PROGS instances for MPICC et al fall back on $CC in the
not-found case. Without that, and given some argument to the ACX_MPI
macro could make it safely override before expanding AC_PROG_CC.
Suggested patch attached (in format suitable for piping to 'git am -3').
Thanks,
Ralf
>From a7ed24ccfb253faec3ecfec3abdfdc89d0c460a5 Mon Sep 17 00:00:00 2001
From: Ralf Wildenhues <[email protected]>
Date: Sat, 31 Jul 2010 17:46:48 +0200
Subject: [PATCH] Fix recommendation for compiling everything with MPI.
* m4/ax_mpi.m4: Fix typos when compiling everything with MPI.
Update description to include defaulting CC to MPICC if only
the latter was set.
---
m4/ax_mpi.m4 | 17 +++++++++++++----
1 files changed, 13 insertions(+), 4 deletions(-)
diff --git a/m4/ax_mpi.m4 b/m4/ax_mpi.m4
index 06c0abd..9607203 100644
--- a/m4/ax_mpi.m4
+++ b/m4/ax_mpi.m4
@@ -19,10 +19,19 @@
# are needed for linking MPI (e.g. -lmpi or -lfmpi, if a special
# MPICC/MPICXX/MPIF77/MPIFC was not found).
#
-# If you want to compile everything with MPI, you should set:
-#
-# CC="MPICC" #OR# CXX="MPICXX" #OR# F77="MPIF77" #OR# FC="MPIFC"
-# LIBS="$MPILIBS $LIBS"
+# If you want to compile everything with MPI, you should use something like
+# this for C:
+#
+# if test -z "$CC" && test -n "$MPICC"; then
+# CC="$MPICC"
+# fi
+# AC_PROG_CC
+# AX_MPI
+# CC="$MPICC"
+# LIBS="$MPILIBS $LIBS"
+#
+# and similar for C++ (change all instances of CC to CXX), Fortran 77
+# (with F77 instead of CC) or Fortran (with FC instead of CC).
#
# NOTE: The above assumes that you will use $CC (or whatever) for linking
# as well as for compiling. (This is the default for automake and most
--
1.7.2.rc3.47.g996ce
