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Re: How to create tests for FC?

From: Steven G. Johnson
Subject: Re: How to create tests for FC?
Date: Tue, 7 Jun 2005 17:01:49 -0400 (EDT)

tests should also normally use AC_COMPILE_IFELSE which uses the current
extension and flags (if any).

Not so good.  Currently, libtool.m4 uses $ac_compile but modifies it so
that the compiler flag we are currently testing comes right after the
last *FLAGS variable, if any, or before the first word that matches
`conftest.', or at the end.  This is (I believe) so that it works with
several Autoconf versions, programming languages, compilers, and I feel
quite uneasy changing it for the established languages, as this code has
evolved a long time.  Now I guess that macro breaks $FCFLAGS_$SRCEXT use
which needs to come right before the source file name.  :(

I don't think you have any choice here. For the Intel compiler, the -Tf flag has to come immediately before the source file. So, you have to modify your behavior, at least for Fortran.

I would suggest that you let autoconf decide what is the right place to put compiler flags, rather than munging ac_compile. libtool is not the right place for this sort of knowledge.

The link tests use $ac_link. I do not know whether the compiler will select different linker flags and libraries for different $SRCEXT values, but I could imagine this, seeing that compilers _do_ select different values for FLIBS and FCLIBS. It would mean that libtool has to know the source extension which the user will later use (or maybe the highest one), so that the correct libs can be added to shared library deplibs. Hmm, maybe we should just require the user to put AC_FC_SRCEXT before AC_PROG_LIBTOOL/LT_INIT?

What if the user mixes code with more than one extension? e.g. some .f90 files and some .f95 files? This needs to work too.

I think the most reasonable course, for now, is to assume that a given compiler name $FC always uses the same libs; if we find a specific case where this fails we can find a workaround, but it is impractical to work around completely hypothetical failures, especially since it's not clear what the solution should be.

(Differences between $FLIBS and $FCLIBS probably stem from $FC being different from $F77.)

2) For an eventual test suite addition, should I use `.f90' (so Automake
plays halfway well) and AC_FC_SRCEXT([.f90]), or stick fo `.f'?

It depends on what your test suite needs to do?

It should test creating shared libraries with Fortran code and mixed
Fortran/C code and a program that uses them.  Maybe also Fortran 77/
Fortran, but I suspect that will be less of an issue in practice.

I would stick with the autoconf default (.f, or whatever the user selected).

A workaround is to set F77=$FC and FFLAGS=$FCFLAGS

Not good.  Recent automake also issues `--tag=F77' resp. `--tag=FC' for
the libtool command line.  We need this to be correct as well so libtool
selects the right flags.

If FC=F77, then why shouldn't --tag=F77 be okay?

In any case, any more sophisticated fix relies on automake being fixed. It should use FC for .f files if AC_FC_SRCEXT(f) was called by the user.

Adding it to FCFLAGS will almost certainly cause other failures (because
e.g. FCFLAGS are used for linking as well as for compiling).

This is one question I did not know but have not tested thoroughly yet.
Do you know of a system where this fails?

I suspect the Intel compiler will fail. -Tf tells it that the next thing on the command line is a Fortran source file, and if it isn't I seem to recall an error occurring. (The Intel compiler is the whole reason that the AC_FC_SRCEXT documentation insists that its flag go immediately before the source file.)


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