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Re: BCT optimization
- To: law at cygnus dot com
- Subject: Re: BCT optimization
- From: David Edelsohn <dje at watson dot ibm dot com>
- Date: Sun, 20 Sep 1998 23:18:24 -0400
- Cc: Michael Hayes <m dot hayes at elec dot canterbury dot ac dot nz>, egcs at cygnus dot com
>>>>> Jeffrey A Law writes:
Jeff> Yup. That's the right fix, and one of the ones I'd done to a local
Jeff> tree, but never finished. Similarly with the formatting stuff. That
Jeff> work is getting rather old, but might be useful. If you'd like I can
Jeff> send it (I didn't even bother to try and compile it at the time).
When you have a chance, I wouldn't mind seeing the changes you
made. I don't have a lot of time to devote to this, so I am not sure how
fast it will get done.
The main thing I noticed is that the BCT stuff duplicates a lot of
code for computing a loop with a constant number of iterations -- and does
a worse job. I am planning to rip that out and use loop_n_iterations for
loops whose iteration count can be pre-determined. I am not going to
touch the runtime bounds stuff. Using loop_n_iterations, I also can avoid
using the counter for loops that have too few iterations to be effective
and possibly allow an outer loop with more iterations utilize the
resource.
Issues that I still need to understand are when loop_n_iterations
is valid. Some loop parameters are stored in a vector based on loop id
and others, such as loop_n_iterations, are not. Also, after unrolling,
how must one obtain the correct iteration count.
Thanks, David