This series of patches changes the way accept nodes are generated
and the expression tree is set-up around them. It is a start to the
backend refactoring and cleanup, and provides a nice little performance
boost in most cases because
1. It reduces the number of accept nodes geneted and considered during
simplification/factoring, and node set building (shorter node sets
to construct and compare)
2. It reduces the number of Alt nodes (used to combine the accept nodes)
to consider during simplfication, and node set building (agin shorter
node sets to construct and compare)
3. It reduces the number of nodes that must be consider in any given
simplification pass, by separating out node sets that can't be
simplified on the right hand simplification/factoring pass.
The performance change is dependent on the profile being parsed, and
there is no guarentee that it will be faster for all profiles. With that
being said, I haven't seen any performance regressions+ and some fairly
nice performance improvements so its worth considering before the rest
of the backend factoring is done.
Eg. Using a few example profile tests from a local machine, comparing
against the 2.9 parser in Ubuntu 14.10 against current 2.10 with
these patches*
profile with tree simplification -O no-expr-simplify
------- ----------------------- -------------------
evince 22% faster 10% faster
firefox 40% faster 11% faster
chromium 32% faster 11% faster
cupsd 35% faster 3% faster
dnsmasq 12% faster 17% faster
dhclient 36% faster 5% faster
klogd 0% 8% faster
*Note: 2.10 is actually handicapped by a couple fixes to change_profile
encoding that causes its dfa to have a few extra nodes.
+There was some regression, in a few cases on individual runs but when
averaged over a few runs, the timing variations resulted in small net
wins, in those cases.
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