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Simon Peyton Jones authored
This patch does a lot of tidying up of the way that dead variables are handled in Core. Just the sort of thing to do on an aeroplane. * The tricky "binder-swap" optimisation is moved from the Simplifier to the Occurrence Analyser. See Note [Binder swap] in OccurAnal. This is really a nice change. It should reduce the number of simplifier iteratoins (slightly perhaps). And it means that we can be much less pessimistic about zapping occurrence info on binders in a case expression. * For example: case x of y { (a,b) -> e } Previously, each time around, even if y,a,b were all dead, the Simplifier would pessimistically zap their OccInfo, so that we can't see they are dead any more. As a result virtually no case expression ended up with dead binders. This wasn't Bad in itself, but it always felt wrong. * I added a check to CoreLint to check that a dead binder really isn't used. That showed up a couple of bugs in CSE. (Only in this sense...
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