#7116: Missing optimisation: strength reduction of floating-point multiplication --------------------------------------------+------------------------------ Reporter: simonmar | Owner: pcapriotti Type: bug | Status: new Priority: normal | Milestone: 7.8.1 Component: Compiler | Version: 7.4.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Runtime performance bug | Unknown/Multiple Test Case: | Difficulty: Unknown Blocking: | Blocked By: | Related Tickets: --------------------------------------------+------------------------------ Comment (by jstolarek): Provded patch rewrites 2 * x for Int and Word to x + x, which kills the optimisation done at the later stage of the pipeline in !CmmOpt: turning multiplications and divisons by powers of two into shifts. I wonder if it makes sense to move mentioned Cmm optimisation to !PrelRules, so that shifts are introduced at the Core level. Having all similar optimisations done in one place would be more consistent. Or am I missing something? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/7116#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler