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Re: Comparing Linux C and C++ Compilers: Benchmarks and Analysis

On Sat, 18 Sep 2004, Richard Guenther wrote:

You may want to check gcc 4.0s auto-vectorizing capabilities by using -ftree-vectorize. I believe Intel compiler does this by default with your optimization settings, and also unrolls loops where profitable (-funroll-loops for all gcc versions). While I personally do not have success with auto-vectorizing (neither with Intel nor with gcc), loop unrolling shows very positive effects on my numerical codes.

I tried compiling scimark with gcc 4 with -ftree-vectorize -msse2 -fdump-tree-vect-stats and again with the lno branch. This was with a P4 on Fedora Core 2. Looking at the generated .vect files, it looked like gcc wasn't able to vectorize any of the loops in scimark, which is a bit diappointing. It's possible I didn't use it correctly I suppose.


Jeremy Sanders <>
X-Ray Group, Institute of Astronomy, University of Cambridge, UK.
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