#14644: Improve cmm/assembly for pattern matches with two constants. -------------------------------------+------------------------------------- Reporter: AndreasK | Owner: AndreasK Type: task | Status: patch Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 (CodeGen) | Keywords: Codegen, CMM, Resolution: | Patterns, Pattern Matching Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D4294 Wiki Page: | -------------------------------------+------------------------------------- Comment (by Ben Gamari <ben@…>): In [changeset:"7ff6023537fdef32bbe9b4c357012d705d9b931f/ghc" 7ff6023/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="7ff6023537fdef32bbe9b4c357012d705d9b931f" cmm: Use two equality checks for two alt switch with default For code like: f 1 = e1 f 7 = e2 f _ = e3 We can treat it as a sparse jump table, check if we are outside of the range in one direction first and then start checking the values. GHC currently does this by checking for x>7, then x <= 7 and at last x == 1. This patch changes this such that we only compare for equality against the two values and jump to the default if non are equal. The resulting code is both faster and smaller. wheel-sieve1 improves by 4-8% depending on problem size. This implements the idea from #14644 Reviewers: bgamari, simonmar, simonpj, nomeata Reviewed By: simonpj, nomeata Subscribers: nomeata, simonpj, rwbarton, thomie, carter Differential Revision: https://phabricator.haskell.org/D4294 }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14644#comment:15> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler