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Re: Loop unrolling



  In message <199809171822.LAA23671@Canada.AI.SRI.COM>you write:
  > The technical problems are:
  > 
  > 1) Semi-reliably determine that a loop terminates (the constraint is
  >    all one-sided in that we can never delete a loop unless we can
  >    prove that it terminates).
Absolutely correct.

  > 2) Determining whether a loop is empty or not needs some kind of
  >    register lifetime information.  Last I looked, this was not
  >    reliable at the time of loop unrolling.  If this is no longer true,
  >    then I can resurrect some code to do this.
Maybe I misunderstood the kinds of loops people wanted to eliminate.
I thought if they were empty there was nothing but an increment of
the counter, and a condjump back to the counter increment.

Obviously we can not eliminate a loop if we can not prove doing so
is safe.

jeff


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