[Bug regression/33928] [4.3 Regression] 22% performance slowdown from 4.2.2 to 4.3.0 in floating-point code

["lucier at math dot purdue dot edu" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #11 from lucier at math dot purdue dot edu  2007-11-12 21:50 -------
I suspected that the slowdown had nothing to do with computed gotos, so I
regenerated the C code using a switch instead of the computed gotos and got the
following:

For that same copy of mainline

gcc version 4.3.0 20071026 (experimental) [trunk revision 129664] (GCC) 

:

(time (direct-fft-recursive-4 a table))
    470 ms real time
    470 ms cpu time (470 user, 0 system)
    no collections
    64 bytes allocated
    no minor faults
    no major faults

For 4.2.2:

(time (direct-fft-recursive-4 a table))
    384 ms real time
    384 ms cpu time (383 user, 1 system)
    no collections
    64 bytes allocated
    no minor faults
    no major faults

So that's almost exactly the same slowdown as with computed gotos.

I changed the subject line to use 22% instead of 33% (I don't know how I got
33% before, perhaps I just mistyped it) and removed the phrase "with computed
gotos".

I'll include the new .i and .s files as attachments.


-- 

lucier at math dot purdue dot edu changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[4.3 Regression] 33%        |[4.3 Regression] 22%
                   |performance slowdown from   |performance slowdown from
                   |4.2.2 to 4.3.0 in floating- |4.2.2 to 4.3.0 in floating-
                   |point code with computed    |point code
                   |gotos                       |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33928