CCL: ifc -O0 failure

From: caroline taylor <cmtaylor_at_kff1.uchicago.edu>
Subject: CCL: ifc -O0 failure
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
 ---------------------------------------------