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Re: Optimizer Problem
- From: Stefanos Folias <sf at math dot bu dot edu>
- To: fortran at gcc dot gnu dot org
- Date: Tue, 4 Jul 2006 17:35:28 -0400
- Subject: Re: Optimizer Problem
Yesterday I reported a problem I was having with optimizers on
gfortran. The bug seems to generate different output with optimizers
on, but only if the array size is sufficiently large. The problem
persisted through a previous update(march?). I have updated again
(yesterday) to the latest version
gcc version 4.2.0 20060512 (experimental)
and the problem still occurs. I obtain the same output for -O, -O2, -
O3. In the cases of no optimization and --fast-math I find the same
output, which differs from -O, if one dimension of the array
increases in length through a critical value.
Are there other optimizers that I could try? --fast-math didn't
improve the speed very much, especially compared to -O (4-5 fold).
It will take me a little time to find a suitable reduced test case,
especially since, at one point, I realized the discrepancy could not
only be generated by different array sizes, but also on the inclusion
of an irrelevant variable declaration!!!
In the case that the bug is my problem, what's the best way to
determine this. I occasionally use an older ftnchk, disregarding
obsolete warnings. What might be more appropriate?
Thanks
Stefanos