[Bug c/35709] New: severe perfromance degradation with "float complex" type

[sergstesh at yahoo dot com]

Compiling and running the same test case with gcc-4.2.3 and gcc-4.3.0 shows
that in the latter case performance takes an almost 3x hit:

"
sergei@amdam2:/mnt/sda1/sergei/learning_octave>
/maxtor5/sergei/AppsFromScratchWD/install/gcc-4.2.3/binsh/gcc -Wall
-mtune=native -march=native -O2 -msse -lm complex_multiplication_testcase.c -o
complex_multiplication_testcase
sergei@amdam2:/mnt/sda1/sergei/learning_octave> time
./complex_multiplication_testcase
executions of straightforward_multiply_with_ptrs() took 6.77 seconds at line
number 136 of 'complex_multiplication_testcase.c' file
executions of straightforward_multiply() took 6.74 seconds at line number 154
of 'complex_multiplication_testcase.c' file
executions of straightforward_multiply_2_signals() took 8.62 seconds at line
number 172 of 'complex_multiplication_testcase.c' file

real    0m22.326s
user    0m22.121s
sys     0m0.012s
sergei@amdam2:/mnt/sda1/sergei/learning_octave>
/maxtor5/sergei/AppsFromScratchWD/install/gcc-4.3.0/binsh/gcc -Wall
-mtune=native -march=native -O2 -msse -lm complex_multiplication_testcase.c -o
complex_multiplication_testcase
sergei@amdam2:/mnt/sda1/sergei/learning_octave> time
./complex_multiplication_testcase
executions of straightforward_multiply_with_ptrs() took 18.17 seconds at line
number 136 of 'complex_multiplication_testcase.c' file
executions of straightforward_multiply() took 16.91 seconds at line number 154
of 'complex_multiplication_testcase.c' file
executions of straightforward_multiply_2_signals() took 30.64 seconds at line
number 172 of 'complex_multiplication_testcase.c' file

real    1m6.306s
user    1m5.676s
sys     0m0.056s
sergei@amdam2:/mnt/sda1/sergei/learning_octave>
"

- see, for example,

executions of straightforward_multiply() took 6.74 seconds
vs
executions of straightforward_multiply() took 16.91 seconds

and

user    0m22.121s
vs
user    1m5.676s
.

FWIW, gcc-3.4.6 shows comparable to gcc-4.2.3 results, albeit slightly worse,
so it looks like the issue is very much gcc-4.3.0 specific.

I'll upload the test case.


-- 
           Summary: severe perfromance degradation with "float complex" type
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: sergstesh at yahoo dot com
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35709