XLF optimizer unreliable, inappropriate for benchmarks

[Warren Jones]

Thanks to ichihara at rkna50.riken.go.jp (Takashi Ichihara) for
posting detailed benchmark results for the Power Station 530.

However, until the XLF optimizer can be trusted, realistic
benchmarks should be compiled with optimization OFF.  It
doesn't matter how fast the machine is if the results are wrong.

I'm including a short fortran program that demonstrates an
optimizer bug that one of our applications people discovered.
For the time being, I will not use the optimizer, period.
It's not worth the grief.

Incidentally -- does anyone know if all the XL languages (including
C and Pascal) use the same optimizer?  Until I'm sure of the
answer, I'm not using the C optimizer either.

------------------------ cut here ---------------------------
#! /bin/sh
# This is a shell archive, meaning:
# 1. Remove everything above the #! /bin/sh line.
# 2. Save the resulting text in a file.
# 3. Execute the file with /bin/sh (not csh) to create the files:
#	README
#	bug.f
#	Makefile
#	bugdemo
# This archive created: Wed Sep 19 12:54:26 1990
export PATH; PATH=/bin:$PATH
echo shar: extracting "'README'" '(884 characters)'
if test -f 'README'
then
	echo shar: will not over-write existing file "'README'"
else
sed 's/^X//' << \SHAR_EOF > 'README'
X
XThis is a test program that demonstrates a bug in the XLF fortran
Xcompiler under AIX 3.1.  The applications programmer who discovered
Xthe problem has tried a number of variations, and this code seems to
Xbe the minimum required to reproduce the bug in a predictable manner.
X
XIBM problem number:  1X991
X
XWe are running AIX 3.1 on a RISC6000-530.
XHere is some version information produced by "lslpp -h":
X
XOption Name          State      Event      Date/Time Release         User Name
X-------------------- ---------- ---------- --------- --------------- ----------
Xxlfcmp.obj           ACTIVE     COMMIT     07/14/90  01.01.0000.0000 root
Xxlfrte.obj           ACTIVE     COMMIT     07/14/90  01.01.0000.0000 root
X
XWarren Jones                  Sept 5, 1990
XGolder Associates Inc.
X4104 148th Ave NE             (206)  883-0777
XRedmond, WA 98052             email:  golder at nwnexus.wa.com
X
SHAR_EOF
if test 884 -ne "`wc -c < 'README'`"
then
	echo shar: error transmitting "'README'" '(should have been 884 characters)'
fi
fi # end of overwriting check
echo shar: extracting "'bug.f'" '(1017 characters)'
if test -f 'bug.f'
then
	echo shar: will not over-write existing file "'bug.f'"
else
sed 's/^X//' << \SHAR_EOF > 'bug.f'
Xc-----------------------------------------------------------------
X      program bug
Xc
Xc  This code demonstrates an optimizer bug in the XLF fortran
Xc  compiler under  AIX 3.1.  It seems to be the minimum required
Xc  to reproduce the bug in a predictable manner.  Compile with and
Xc  without the XLF optimizer turned on, and compare the results.
Xc
Xc  Warren Jones                  Sept 5, 1990
Xc  Golder Associates Inc.
Xc  4104 148th Ave NE             (206)  883-0777
Xc  Redmond, WA 98052             email:  golder at nwnexus.wa.com
Xc-----------------------------------------------------------------
X
X      integer*4 b, i, k, m, n
X      logical*4 test
Xc
X      test = .true.
X      m  = 0
X      k  = 0
X      i  = 0
Xc
X  10  continue
X      i = i + 1
X      if (test) then
X        do 2 n = 1, 3
X          m  = m + 1
X          k  = k + 1
X          b  = k + 1
X   2    continue
X        write (*,'(a,i6)')' k     = ',k
X        write (*,'(a,i6)')' k - 1 = ',k - 1
X      end if
X      if (i .lt. 2) goto 10
Xc
X      stop
X      end
X
SHAR_EOF
if test 1017 -ne "`wc -c < 'bug.f'`"
then
	echo shar: error transmitting "'bug.f'" '(should have been 1017 characters)'
fi
fi # end of overwriting check
echo shar: extracting "'Makefile'" '(223 characters)'
if test -f 'Makefile'
then
	echo shar: will not over-write existing file "'Makefile'"
else
sed 's/^X//' << \SHAR_EOF > 'Makefile'
X#! /bin/make -f
X#
X#  Makefile to demonstrate an optimizer bug
X#  in the XLF fortran compiler under AIX 3.1.
X
Xbug.out : bug nobug
X	bugdemo 2>&1 | tee bug.out
X
Xbug : bug.f
X	xlf -O -o $@ bug.f
X
Xnobug : bug.f
X	xlf -o $@ bug.f
X
SHAR_EOF
if test 223 -ne "`wc -c < 'Makefile'`"
then
	echo shar: error transmitting "'Makefile'" '(should have been 223 characters)'
fi
fi # end of overwriting check
echo shar: extracting "'bugdemo'" '(100 characters)'
if test -f 'bugdemo'
then
	echo shar: will not over-write existing file "'bugdemo'"
else
sed 's/^X//' << \SHAR_EOF > 'bugdemo'
X#! /bin/sh
X
Xecho
Xecho "NOBUG (Optimization OFF)"; nobug
X
Xecho
Xecho "BUG   (Optimization ON) "; bug
X
SHAR_EOF
if test 100 -ne "`wc -c < 'bugdemo'`"
then
	echo shar: error transmitting "'bugdemo'" '(should have been 100 characters)'
fi
chmod +x 'bugdemo'
fi # end of overwriting check
#	End of shell archive
exit 0
-- 
----------------------------------------------------------------
Warren Jones <golder at nwnexus.wa.com>      Golder Associates Inc.
(uucp: uunet!nwnexus!golder)              4104 148th Avenue NE
(206) 883-0777                            Redmond, WA 98052, USA