Mon Dec 3 07:00:39 PST 2007 [EMAIL PROTECTED]
* Improve eta reduction, to reduce Simplifier iterations
I finally got around to investigating why the Simplifier was sometimes
iterating so often. There's a nice example in
Text.ParserCombinators.ReadPrec,
which produced:
NOTE: Simplifier still going after 3 iterations; bailing out. Size = 339
NOTE: Simplifier still going after 3 iterations; bailing out. Size = 339
NOTE: Simplifier still going after 3 iterations; bailing out. Size = 339
No progress is being made. It turned out that an interaction between
eta-expansion, casts, and eta reduction was responsible. The change is
small and simple, in SimplUtils.mkLam: do not require the body to be
a Lam when floating the cast outwards.
I also discovered a missing side condition in the same equation, so fixing
that is good too. Now there is no loop when compiling ReadPrec.
Should do a full nofib run though.
M ./compiler/simplCore/SimplUtils.lhs -8 +26
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