This is the mail archive of the
gcc@gcc.gnu.org
mailing list for the GCC project.
Re: (a+b)+c should be replaced by a+(b+c)
Laurent GUERBY wrote:
Could you try -funroll-all-loops and may be a prefetch flag? On short
numerical loops this usually makes lots of difference.
gfortran -o matmulg -O3 -ffast-math -march=pentium4 \
-fprefetch-loop-arrays -funroll-all-loops -mfpmath=sse matmul.for
..does not improve matters. Perhaps this is due to the nascent nature of
gfortran?
As it is, I'm going to stop doing on-the-spot benchmarks for this set of
topics, having demonstrated my assertions about performance and
accuracy. At this point, we're using anecdotal evidence to pick compiler
options; I prefer a more scientific approach.
By Monday, my new Acovea runs (on both P4 and Opteron) will have had a
chance to evolve optimal compiler option sets, showing us where the
strengths and weaknesses lie.
Or so I hope!
..Scott
--
Scott Robert Ladd
Coyote Gulch Productions (http://www.coyotegulch.com)
Software Invention for High-Performance Computing