Dear devs, in https://ghc.haskell.org/trac/ghc/ticket/10124 bgamari suggested that code like f :: Int -> Bool f a = case a of 1 -> True 5 -> True 8 -> True 9 -> True 11 -> True 19 -> True _ -> False {-# NOINLINE f #-} should not compile to a series of conditional jumps, but rather a branchless code akin to let !p = a ==# 1 `orI#` a ==# 5 `orI#` a ==# 8 `orI#` a ==# 9 `orI#` a ==# 11 `orI#` a ==# 19 case p of 1 -> do_something 0 -> do_something_else Subsequently, I refactored the way we produce Cmm code from STG, opening the possibility to implement this optimization at that stage¹. But when I then added this implementation, I could not measure any runtime improvement, see https://ghc.haskell.org/trac/ghc/ticket/10124#comment:15 So my question to the general audience: Is such branchless code really better than the current, branching code? Can someone provide us with an example that shows that it is better? Do I need to produce different branchless assembly? If it is not better, I can again refactor the switch generation and simplify it a bit again. Hmm, only now I see that rwbarton has replied there. Not sure why I missed that. Anyways, more voices are welcome :-) Greetings, Joachim ¹ This should not preclude an implementation on the Core level, which SPJ preferred. But I improved other aspects of the code generation as well, so this is worthwhile on its own. -- Joachim “nomeata” Breitner mail@joachim-breitner.de • http://www.joachim-breitner.de/ Jabber: nomeata@joachim-breitner.de • GPG-Key: 0xF0FBF51F Debian Developer: nomeata@debian.org