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Compilation perfomance of the enclosed test regressed when the
new pattern matcher was introduced, specifically when the tail
call elimination phase was made aware of its tree shapes in cd3d34203.
The code added in that commit detects an application to a tail label
in order to treat recursive calls in the argument as in tail position.
If the transform of that argument makes no change, it falls
back to `rewriteApply`, which transforms the argument again
(although this time on a non-tail-position context.)
This commit avoids the second transform by introducing a flag
to `rewriteApply` to mark the arguments are pre-transformed.
I don't yet see how that fixes the exponential performance, as
on the surface it seems like a constant factor improvement.
But the numbers don't lie, and we can now compile the test
case in seconds, rather than before when it was running for
> 10 minutes.
This test case was based on a code pattern generated by the Avro
serializer macro in:
https://github.com/paytronix/utils-open/tree/release/2014/ernststavrosgrouper
The exponential performance in that context is visualed here:
https://twitter.com/dridus/status/519544110173007872
Thanks for @rmacleod2 for minimizing the problem.
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