#7337: GHC does not generate great code for bit-level rotation -------------------------------------+------------------------------------- Reporter: bos | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler (NCG) | Version: 7.6.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by jberryman): FWIW I'm trying my hand at this, though it may take me a while as it's my first time working on GHC, and I'm not sure how much time I'll have to spend. It looks like I can take my lead from the byteswap patches (`git show 5ae238504 da7db19 1c5b0511 c5d5e3ac 86ca77ecb`). Also I'm considering just implementing a rotateR primop since that's what ARM supports (I think) and my use case only has constant rotate values which I know GHC would simplify to a single instruction if Data.Bits.rotateL was implemented in terms of the rotateR primop. Hm, but that would be extra bad for people who have variable left rotate values which also might be `0`, because they's need to do a AND mask and a subtraction. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/7337#comment:8 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler