[Bug middle-end/35343] Sum-reduction loop not recognized

[xinliangli at gmail dot com]

------- Comment #2 from xinliangli at gmail dot com  2008-02-25 21:36 -------
(In reply to comment #1)
> (In reply to comment #0)
> > It is beneficial to unroll reduction loop (and split the reduction target) to
> > reduce dependence height due to recurrence, but GCC does not perform such
> > optimization (-O3 -fno-tree-vectorize)
> 
> it does, if you use -fvariable-expansion-in-unroller -funroll-loops
> (this splits the reduction target into 2 accumulators. For more agressive
> spiltting you can use --param max-variable-expansions-in-unrolle=[n])
> 

Thanks, it is good to know the option. It would be good to tune the default
behavior of the optimizer so that better out of box performance can be
achieved. 


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35343