Subject: CCL: ifc -O0 failure

From: caroline taylor <cmtaylor_at_kff1.uchicago.edu>
Date: Mon, 9 Jun 2003 12:35:32 -0500 (CDT)

Dear CCLers,

We have run into an anomoly using the ifc compiler with optimization. When
builing the code we've been using to benchmark, we've used the various
optimization flags, with the following results (numerical result and runtime):
-O0:    6.710886E+07  (21.960u 0.020s 0:22.19 99.0%)
-O1:    1.718282E+08  (17.560u 0.010s 0:17.76 98.9%)
-O2:    1.718282E+08  (17.550u 0.010s 0:17.74 98.9%) 
-O3:    1.718282E+08  (17.580u 0.000s 0:17.75 99.0%)
-O4:    1.718282E+08  (17.570u 0.000s 0:17.75 98.9%)
The 0 level optimization is clearly inconsistent, and far larger than
round off. This has been checked on multiple machines (all linux). 

Has anyone run into this before? Is there a known problem with this level,
or is something else going on? 

The very simple code we've used for checking the compiler is
below: 
PROGRAM tyme
  IMPLICIT NONE
  REAL :: sum
  INTEGER :: i
  INTEGER, PARAMETER :: imax = 100000000
  sum = 0.0
   DO i = 1, imax
      sum = sum + DEXP( DBLE(i)/DBLE(imax) )
  END DO 
  write(*,*) sum, i
END PROGRAM tyme

Thanks for your time!
	Caroline

---------------------------------------------
Dr. Caroline M. Taylor
Department of Chemistry
University of Chicago, James Franck Institute
5640 S. Ellis Avenue
Chicago, Illinois 60637
(773) 702-7223
---------------------------------------------