gfortran 4.3.2 about 3x slower than g77 for scientific application

[VelocideX <jking dot phys at gmail dot com>]

Hi all,

I am running a custom scientific fortran 77 program for scientific purposes
(i.e. it is computationally intensive).

I am on a Intel Core 2 Duo P8700 processor with 4 GB RAM, running OpenSuSE
11.1 64 bit (i.e x86-64 architecture).

Executing the program on identical data is about 3x slower in gfortran than
g77 (v3.3.3-hammer). This seems a serious deficiency given that all the run
time in the program is spent in relatively simple calls. Both versions were
compiled with the flag -O2 only.

Here are the gprof results for the g77:
  %   cumulative   self              self     total
 time   seconds   seconds    calls   s/call   s/call  name
 64.12      2.52     2.52    23679     0.00     0.00  vp_spvoigte__
 19.34      3.28     0.76 28574044     0.00     0.00  voigt_
  6.36      3.53     0.25       12     0.02     0.28  deriv_
  4.33      3.70     0.17 32747695     0.00     0.00  dexpf_
  3.05      3.82     0.12      877     0.00     0.00  vp_chspread__
  1.27      3.87     0.05        1     0.05     0.05  pr_sort__
  0.51      3.89     0.02        1     0.02     0.02  probks_
  0.25      3.90     0.01    23679     0.00     0.00  calcn_
  0.25      3.91     0.01      877     0.00     0.00  vp_chipconv__
  0.25      3.92     0.01       11     0.00     0.00  udchole_
  0.25      3.93     0.01        1     0.01     0.01  pldef_
  0.00      3.93     0.00   550174     0.00     0.00  ucase_

...and for the gfortran (slower version) execution:
  %   cumulative   self              self     total
 time   seconds   seconds    calls   s/call   s/call  name
 43.27      3.28     3.28    33885     0.00     0.00  vp_spvoigte_
 27.04      5.33     2.05     1255     0.00     0.00  vp_subchspread_
 16.36      6.57     1.24 41100608     0.00     0.00  voigt_
  6.99      7.10     0.53 528972139     0.00     0.00  dexpf_
  3.56      7.37     0.27       17     0.02     0.38  deriv_
  0.66      7.42     0.05        1     0.05     0.05  pr_sort_
  0.66      7.47     0.05        1     0.05     0.05  probks_
  0.40      7.50     0.03   478767     0.00     0.00  varythis_
  0.40      7.53     0.03        1     0.03     7.52  vp_ucoptv_
  0.26      7.55     0.02    33878     0.00     0.00  vp_archwav_
  0.13      7.56     0.01    33885     0.00     0.00  calcn_
  0.13      7.57     0.01     1255     0.00     0.00  vp_chipconv_
  0.13      7.58     0.01        1     0.01     0.01  vp_gwclinfits_
  0.00      7.58     0.00   793778     0.00     0.00  ucase_

vp_subchspread grows massively in usage time, and it is simply a convolution
routine. I have attached the source code for that routine.
http://www.nabble.com/file/p23527805/vp_subchspread.f vp_subchspread.f .

It's worth noting that dexpf() gets massively slower as well, which is
bizarre. It's a glibc call, I would have thought there shouldn't be an issue
with this.

Any help is appreciated. The program runs fine on g77, but I want to
parallelize with OpenMPI, which requires gfortran (AFAIK it can't be used
with g77).

Many thanks,
Julian
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