Potential optimization problems on Ultras

[Chris Flatters]

We have discovered what appears to be a defect in the code generator of
the SunSoft Workshop FORTRAN compiler, version 4.2.  This version of the
compiler appears to generate bad code for some AIPS routines at optimization
level 3 if the -xchip=ultra or -xtarget=ultra options are used.  The
problem appears to be rare but the subroutines UVPREP and QWTSUM are known
to be affected.

This problem may also exist in version 4.0 of the compiler.  You can check
whether your AIPS installation is affected by this problem by running IMAGR
with ROBUST=5: if the program reports that the noise has been increased by
a factor that differs from unity then you have this problem.

If you are running AIPS on a SPARCstation Ultra and have specifically
compiled your version of AIPS for maximal performance on the Ultra then
I recommend that you remove -xchip=ultra and -xtarget=ultra from the
compilation flags in FDEFAULT.SH, CCOPTS.SH and LDOPTS.SH until this
problem is resolved.  You should also rerun INSTEP2 and INSTEP4 to make
sure that all subroutines and programs have been recompiled.

	Chris Flatters
	cflatter at nrao.edu