Fortran flags

[John W. Eaton]

On 10-May-2011, Jordi Gutiérrez Hermoso wrote:

| On 10 May 2011 10:12, Daniel Kraft <address@hidden> wrote:
| 
| > Usually, -O2 should be a good thing for gfortran.  And in general, please
| > report any "problems" -O2 causes as gfortran bug.
| 
| I was wondering why it's not enabled in the default Fortran flags.
| Instead we merely use -O. I thought the option enabled other
| optimisation flags that caused problems. Red Hat for example broke ABI
| compatibility by compiling with -O2:
| 
|      https://bugzilla.redhat.com/show_bug.cgi?id=478856
| 
| I seem to recall there was another packaging problem by compiling with
| -O2, but I can't find it now.

I no longer remember why the configure script does this:

  ## Default FFLAGS is -O.
  if test "x$FFLAGS" = x; then
    FFLAGS="-O"
  fi

instead of allowing autoconf to select the default.  Maybe we should
let autoconf set the default value now.

jwe