[Bug fortran/39087] New: Performance using COMPLEX data type

[Bug fortran/39087] New: Performance using COMPLEX data type

[m4341 at abc dot se]

I have noticed that in some cases - especially calculating Mandelbrot Fractals
there is a severe performance penalty if the COMPLEX data type is used instead
of plain variables.

It's nothing wrong with the calculation, but it shall be noted that it can mean
a severe performance penalty if the COMPLEX data type is used.

Result of test cases I have created:
---
[root@cvs2 frac]# time ./m6

real    0m5.806s
user    0m1.705s
sys     0m0.032s
[root@cvs2 frac]# time ./m7

real    0m18.598s
user    0m12.469s
sys     0m0.036s

---


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           Summary: Performance using COMPLEX data type
           Product: gcc
           Version: 4.3.3
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: fortran
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: m4341 at abc dot se


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39087

[Bug fortran/39087] Performance using COMPLEX data type

[m4341 at abc dot se]

------- Comment #1 from m4341 at abc dot se  2009-02-03 15:46 -------
Created an attachment (id=17234)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=17234&action=view)
Test cases for demonstrating performance impact.

The attached file contains code that is in it's current state requiring
Xwindows, but it's completely optional for the test case and is only used to
display the result.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39087

[Bug fortran/39087] Performance using COMPLEX data type

[m4341 at abc dot se]

------- Comment #2 from m4341 at abc dot se  2009-02-03 15:50 -------
Notice that the test cases have been executed on a Pentium III computer with
dual 866MHz processors.

The 'depth' variable in the example code has been set to produce comfortable
execution times for the forementioned computer.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39087

[Bug fortran/39087] Performance using COMPLEX data type

[rguenth at gcc dot gnu dot org]

------- Comment #3 from rguenth at gcc dot gnu dot org  2009-02-03 16:15 -------
Use -ffast-math.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39087

[Bug fortran/39087] Performance using COMPLEX data type

[bonzini at gnu dot org]

------- Comment #4 from bonzini at gnu dot org  2009-02-03 16:52 -------
more precisely, without -ffast-math gcc is not able to change abs(z) < 2 to
r*r+i*i < 4 and computes a square root on every iteration.


-- 

bonzini at gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39087