when comparing the Invel V7 compiler for Linux with GNU gcc2 and gcc3 we had some test cases where the Intel compiler was significantly slower than gcc. Even playing with the optimization options (-O3 -ipo -tpp7 -xW) did not close the performance gap *if* certain C++ features explained below where used. Example : FFT (attached)
gcc 2.95.3 : 30.8s
gcc 3.2.1 : 24,2s
icc 7 build 20021021Z : 45.8s
System : P4 1.7 GHz, 512 MB RAM
The performance gap increases, if templates are extensively used. Profiling showed that larger template classes are often not inlined, even if the maximum template size for inlining in increased via command line option.
Are there other possibilities to enhance performance of our code ? People where reporting amazing performance increases up to 30% we would like to share :).
Thank you in advance,
ICC vs. GCC