#14684: combineIdenticalAlts is only partially implemented -------------------------------------+------------------------------------- Reporter: mpickering | Owner: sjakobi Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.2.2 Resolution: | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D4542 Wiki Page: | -------------------------------------+------------------------------------- Changes (by sjakobi): * cc: dfeuer (added) Comment: Replying to [comment:11 simonpj]: Thanks for your comments, Simon! I realized that if I apply the combine-most-common-alts optimization ''only'' in `CSE.combineAlts`, we'd get "suboptimal" results in cases like this: {{{#!hs case x of A -> 1 B -> 1 C -> 2 D -> 2 E -> 2 }}} Here, `combineIdenticalAlts` (which in my understanding runs first) would combine the `A` and `B` alts, defeating `CSE.combineAlts` which could combine `C`, `D` and `E`. I'm not sure if this warrants doing the optimization in both places with `-O2`. ------------- I also noticed that unlike `combineIdenticalAlts` `CSE.combineAlts` doesn't combine the ticks of the identical alts. Would you, David, happen to know why this is permissible in this case? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14684#comment:12 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler