Grepping for "Class op" brought up a candidate for the first rule: ./compiler/basicTypes/MkId.lhs-313- -- This is the built-in rule that goes -- op (dfT d1 d2) ---> opT d1 d2 A few other greps let me think that the other rule is probably one of those generated by the function primOpRules in ./compiler/prelude/PrelRules.lhs which is called from ./compiler/basicTypes/MkId.lhs:911 The following comment can be found in the file: "Note [Constant folding] ~~~~~~~~~~~~~~~~~~~~~~~ primOpRules generates a rewrite rule for each primop These rules do what is often called "constant folding" E.g. the rules for +# might say 4 +# 5 = 9 Well, of course you'd need a lot of rules if you did it like that, so we use a BuiltinRule instead, so that we can match in any two literal values. So the rule is really more like (Lit x) +# (Lit y) = Lit (x+#y) where the (+#) on the rhs is done at compile time That is why these rules are built in here." Hope this helps, Thomas Am 28.08.2014 um 22:40 schrieb Dominik Peteler:
Dear Cafe,
I'm currently looking at the optimization GHC is doing and I cannot find the rewrite rules it fires. When I run my test code with
ghc -O2 -ddump-simpl-stats -ddump-rule-firings Main.hs
GHC shows the rules which are fired:
... Rule fired: Class op + ... Rule fired: +## ...
and so on. Nothing new, nothing special. However, where do I find the definitions of these rules ? I grepped[1] the GHC code base and found nothing so far. I didn't find any documentation on it either.
Can anyone point me to some place where I can find further information ?
Thank you folks and have a nice day
Dominik
PS.: Since I'm working on numerical stable code with directed rounding I'm only interested in these two particular rules. I suspect them to break parts of my code.
[1] http://jamie-wong.com/2013/07/12/grep-test
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