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Re: [rtlopt] speed improvement of branch prediction
> Speed up the use of real.c instead. See attached patch.
> It gets rid of most divisions in branch prediction.
>
> > real.c already does not do operations bit by bit
> > but by groups of bits (size of unsigned long)
> > so I do not know how to speed it up.
>
> It does do division bit by bit.
Yes, division is done bit by bit, but (at least some) other operations
are on groups.
> This patch achieves a speedup of GCC by a few percent on compiling
> combine.c; any suggestions for better compile-time benchmarks gladly
> accepted.
This patch is a good idea. I have bootstrapped it on i386 (athlon),
I'm regtesting it now.
Josef
> 2003-01-08 Segher Boessenkool <segher@koffie.nl>
>
> * predict.c (real_inv_br_prob_base): New variable.
> (propagate_freq): Use multiply by reciprocal instead of
> division. Don't divide by 1.0 at all.
> (estimate_bb_frequencies): Similar.