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Re: DFA lookahead confusion
From: Vladimir Makarov <email@example.com>
Date: Wed, 15 May 2002 12:07:28 -0400
The goal of usage of the parameter is to constrain number of
queue permutation tries. Generally speaking, the value bigger than
queue size will never give the improvement. Maximal queue size is
depended on program not on processor characteristics.
I recommended to use it equal to maximal processor insn issues per clock
as a compromise between the code improvement and compilation time But
it is only heuristic.
Now, if documentation had stated this there would have been no
I think we should determine reasonable value for DFA lookahead that is
a good compromise, based solely on resulting complexity, and use this
value for EVERYONE if scalarity of processor (ie. instructions per
cycle) is greater than one.
Then we can add the knobs to allow the user to adjust this on the