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Currently we have this in libraries/base/GHC/Float.hs: ``` abs x | x == 0 = 0 -- handles (-0.0) | x > 0 = x | otherwise = negateFloat x ``` But 3-4 years ago it was noted that this was inefficient: https://mail.haskell.org/pipermail/libraries/2013-April/019690.html We can generate better code for X86 and llvm and for others generate some custom cmm code which is similar to what the compiler generates now. Reviewers: austin, simonmar, hvr, bgamari Reviewed By: bgamari Subscribers: dfeuer, thomie Differential Revision: https://phabricator.haskell.org/D3265
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