#7796: improve dead code elimination in CorePrep -----------------------------+---------------------------------------------- Reporter: nfrisby | Owner: nfrisby Type: bug | Status: new Priority: normal | Component: Compiler Version: 7.6.2 | Keywords: Os: Unknown/Multiple | Architecture: Unknown/Multiple Failure: None/Unknown | Blockedby: Blocking: | Related: #4962 #5433 -----------------------------+---------------------------------------------- #4962 is about generating code for (and allocating at runtime!) bindings that are kept alive only by RULEs even though the RULEs are useless downstream of .hi file generation. Simon Marlow's patch for #5433 switched to a custom dead code eliminator, since the "(case) binder swap" in OccurAnal was creating breaking some code generator invariants. However, that custom dead code generator doesn't do a dependency analysis, so a letrec like this {{{ let f = [g] \r [...] -> ... g = [g] \r [...] -> ... in ... g ... }}} is sent to the code generator ''without dropping'' `f`. A patch to use a dependency analysis in CorePrep's dead code eliminator improves allocation for several nofib programs (largest: cryptarithm2, knights, fem). {{{ Min -0.0% -4.2% -7.7% -7.7% -5.9% Max +0.0% +0.0% +4.3% +4.3% +14.3% Geometric Mean -0.0% -0.1% -0.2% -0.2% +0.2% }}} -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/7796 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler