topic Re: Possible Fortran 8.2 compiler bug on Itanium in Operating System - OpenVMS

Possible Fortran 8.2 compiler bug on Itanium

Jeremy Begg — Fri, 20 Jul 2012 03:16:02 GMT

HIi,

I am helping a customer port their Fortran applications from OpenVMS Alpha V7.2-2 to OpenVMS IA64 V8.4.

The code (mostly) compiles cleanly but some programs are giving wrong results. For example, when compiling and running the attached file (TMINUSPLUS.FOR) we get wrong values displayed:

$ sho sym fortran
%DCL-W-UNDSYM, undefined symbol - check validity and spelling
$ fortran tminusplus
$ link tminusplus
$ run tminusplus
         18
         20
         20
         18
         20
         20
$

The value being output by the program should be '20' on every line; '18' is incorrect.

It looks like the compiler is evaluatiing the expression

result = FILE.INFO.SEG(1).END - FILE.INFO.SEG(1).START + 1

as if it was written

result = FILE.INFO.SEG(1).END - (FILE.INFO.SEG(1).START + 1)

and in fact the erroneous instruction, as seen in the Debugger, is

sub r9 = r9, r10, 1

The trailing ", 1" has the effect of subtracting 1 from the result, whereas the expression requires 1 be added to the result.

I've tried both the Fortran 8.2 compiler and the 8.2 ECO1 compiler and both give the same results.

I am going to try to report this to HP. If anyone has seen this before, and/or knows a workaround (which hopefully doesn't require extensive code changes!) I'd like to know about it.

Thanks,

Jeremy Begg

Re: Possible Fortran 8.2 compiler bug on Itanium

Steven Schweda — Fri, 20 Jul 2012 04:50:07 GMT

Re: Possible Fortran 8.2 compiler bug on Itanium

Jeremy Begg — Fri, 20 Jul 2012 06:14:21 GMT

Thanks for the info, Steven. HP has acknowledged receipt of my support request so we'll see what happens.

Re: Possible Fortran 8.2 compiler bug on Itanium

Eberhard Heuser — Fri, 20 Jul 2012 07:26:32 GMT

There is a newer fortran version available:

$ fortran/version
HP Fortran V8.2-104953-50M2N

Eberhard

Re: Possible Fortran 8.2 compiler bug on Itanium

Jeremy Begg — Fri, 20 Jul 2012 07:37:20 GMT

Hi Eberhad,

That's the Fortran 8.2 ECO1 release, which gives the same results. In fact that's where we first noticed it.

Jeremy

Re: Possible Fortran 8.2 compiler bug on Itanium

Fekko Stubbe — Fri, 20 Jul 2012 08:07:42 GMT

I tried this on alpha (8.4) with the same result (error)

$fortran/vers

Hp Fortran v8.2-104679-48H9K

If I use the old f77 compiler (fortran/old) the result is correct (all 20s)

$fortran/old/version

HP Fortran 77 V7.6-198-48H9K (this version reports 7.6 while it really is the 8.2 version, another bug)

Re: Possible Fortran 8.2 compiler bug on Itanium

abrsvc — Fri, 20 Jul 2012 10:35:09 GMT

The report of V7.6 is correct as the F77 compiler is a completely different image. F90$main is the F90 compiler while FORT$main is the F77 compiler.

Dan

Re: Possible Fortran 8.2 compiler bug on Itanium

Fekko Stubbe — Fri, 20 Jul 2012 13:28:52 GMT

You could be right, but the image is installed from the fortran 8.2 kit. This kit installs both the fort$main as the f90$main. I find it highly confusing. If they wat to distribute different version for the f90 and the f77 compiler they should have deliverd 2 kits. As far aas I rmember the 8.1 kit distributes an 8.1 version for both compilers.

Re: Possible Fortran 8.2 compiler bug on Itanium

Mike Kier — Fri, 20 Jul 2012 15:57:51 GMT

It worked correctly under the Fortran 95 compiler on a much older Alpha version - running OpenVMS Alpha V7.3-2 and Fortran V7.5-1961-48BCD

Re: Possible Fortran 8.2 compiler bug on Itanium

John Brodribb — Fri, 20 Jul 2012 21:48:18 GMT

This was fixed recently. Please contact your Support Centre for a remedial side image.

Re: Possible Fortran 8.2 compiler bug on Itanium

John Gillings — Mon, 23 Jul 2012 21:58:30 GMT

Jeremy,

If only all "I've found a compiler bug" reports were so well researched, characterised and documented with such a simple and unarguable reproducer! :-)