[cfe-dev] food for optimizer developers
Ralf W. Grosse-Kunstleve
rwgk at yahoo.com
Mon Aug 9 18:52:55 PDT 2010
I wrote a Fortran to C++ conversion program that I used to convert selected
LAPACK sources. Comparing runtimes with different compilers I get:
absolute relative
ifort 11.1.072 1.790s 1.00
gfortran 4.4.4 2.470s 1.38
g++ 4.4.4 2.922s 1.63
clang++ 2.8 (trunk 108205) 6.487s 3.62
This is under Fedora 13, 64-bit, 12-core Opteron 2.2GHz
All files to easily reproduce the results are here:
http://cci.lbl.gov/lapack_fem/
See the README file or the example commands below.
Questions:
- Why is the code generated by clang++ so much slower than the g++ code?
- Is there anything I could do in the C++ code generation or in the "fem"
Fortran EMulation library to help runtime performance?
Ralf
wget http://cci.lbl.gov/lapack_fem/lapack_fem_001.tgz
tar zxf lapack_fem_001.tgz
cd lapack_fem_001
clang++ -o dsyev_test_clang++ -I. -O3 -ffast-math dsyev_test.cpp
time dsyev_test_clang++
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