[Bug c++/69564] lto and/or C++ make scimark2 LU slower
rguenth at gcc dot gnu.org
gcc-bugzilla@gcc.gnu.org
Mon Feb 1 10:22:00 GMT 2016
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69564
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |lto, missed-optimization
Status|UNCONFIRMED |NEW
Last reconfirmed| |2016-02-01
CC| |hubicka at gcc dot gnu.org,
| |rguenth at gcc dot gnu.org
Component|lto |c++
Summary|lto makes scimark2 LU |lto and/or C++ make
|slower |scimark2 LU slower
Ever confirmed|0 |1
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Any reason you are using the c++ driver here?
I get
> gcc-6 -Ofast -flto *.c -lm -B /abuild/rguenther/trunk3-g/gcc
> ./a.out
** **
** SciMark2 Numeric Benchmark, see http://math.nist.gov/scimark **
** for details. (Results can be submitted to pozo@nist.gov) **
** **
Using 2.00 seconds min time per kenel.
Composite Score: 1729.02
FFT Mflops: 1247.04 (N=1024)
SOR Mflops: 1537.70 (100 x 100)
MonteCarlo: Mflops: 842.21
Sparse matmult Mflops: 1657.86 (N=1000, nz=5000)
LU Mflops: 3360.29 (M=100, N=100)
> gcc-6 -Ofast *.c -lm -B /abuild/rguenther/trunk3-g/gcc
> ./a.out
** **
** SciMark2 Numeric Benchmark, see http://math.nist.gov/scimark **
** for details. (Results can be submitted to pozo@nist.gov) **
** **
Using 2.00 seconds min time per kenel.
Composite Score: 1645.94
FFT Mflops: 1288.61 (N=1024)
SOR Mflops: 1471.29 (100 x 100)
MonteCarlo: Mflops: 459.90
Sparse matmult Mflops: 1665.91 (N=1000, nz=5000)
LU Mflops: 3343.98 (M=100, N=100)
Ok, when using g++ to compile things I _do_ get
> g++-6 -Ofast -flto *.c -lm -B /abuild/rguenther/trunk3-g/gcc
> ./a.out
** **
** SciMark2 Numeric Benchmark, see http://math.nist.gov/scimark **
** for details. (Results can be submitted to pozo@nist.gov) **
** **
Using 2.00 seconds min time per kenel.
Composite Score: 1321.43
FFT Mflops: 1261.86 (N=1024)
SOR Mflops: 1533.77 (100 x 100)
MonteCarlo: Mflops: 850.69
Sparse matmult Mflops: 1669.90 (N=1000, nz=5000)
LU Mflops: 1290.93 (M=100, N=100)
> g++-6 -Ofast *.c -lm -B /abuild/rguenther/trunk3-g/gcc
> ./a.out
** **
** SciMark2 Numeric Benchmark, see http://math.nist.gov/scimark **
** for details. (Results can be submitted to pozo@nist.gov) **
** **
Using 2.00 seconds min time per kenel.
Composite Score: 1492.12
FFT Mflops: 1279.12 (N=1024)
SOR Mflops: 1479.86 (100 x 100)
MonteCarlo: Mflops: 433.83
Sparse matmult Mflops: 1637.11 (N=1000, nz=5000)
LU Mflops: 2630.71 (M=100, N=100)
So even without LTO I get a hit in using C++ to compile LU. Interesting.
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