Re: [GHC] #15196: Invert floating point comparisons such that no extra parity check is required.

#15196: Invert floating point comparisons such that no extra parity check is required. -------------------------------------+------------------------------------- Reporter: AndreasK | Owner: AndreasK Type: task | Status: patch Priority: normal | Milestone: 8.8.1 Component: Compiler (NCG) | Version: 8.4.3 Resolution: | Keywords: CodeGen Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D4990 Wiki Page: | -------------------------------------+------------------------------------- Comment (by Krzysztof Gogolewski ): In [changeset:"6bb9bc7d3c935dcb77e0700cce28de2c9df646df/ghc" 6bb9bc7/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="6bb9bc7d3c935dcb77e0700cce28de2c9df646df" Invert FP conditions to eliminate the explicit NaN check. Summary: Optimisation: we don't have to test the parity flag if we know the test has already excluded the unordered case: eg > and >= test for a zero carry flag, which can only occur for ordered operands. By reversing comparisons we can avoid testing the parity for < and <= as well. This works since: * If any of the arguments is an NaN CF gets set. Resulting in a false result. * Since this allows us to rule out NaN we can exchange the arguments and invert the direction of the arrows. Test Plan: ci/nofib Reviewers: carter, bgamari, alpmestan Reviewed By: alpmestan Subscribers: alpmestan, simonpj, jmct, rwbarton, thomie GHC Trac Issues: #15196 Differential Revision: https://phabricator.haskell.org/D4990 }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15196#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler