#7198: New codegen more than doubles compile time of T3294 -------------------------------------+------------------------------------- Reporter: simonmar | Owner: simonmar Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.4.2 (CodeGen) | Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: #4258 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by Ben Gamari ): In [changeset:"6a2264d2bd47e993c43a592bd614ab7917184e22/ghc" 6a2264d/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="6a2264d2bd47e993c43a592bd614ab7917184e22" cmm/CmmLayoutStack: avoid generating unnecessary reloads This tries to be more precise when generating reloads of local registers in proc points. Previously we'd reload all local registers that were live. But we used liveness information that assumed local registers survive native calls. For the purpose of reloading registers this is an overapproximation and might lead to generating huge amounts of unnecessary reloads (in case there's another proc point before the register is used). This change takes the approach of moving the generation of reloads to a second pass over the Cmm, which allows to recompute the liveness and can use the knowledge that local registers do *not* survive calls. This leads to generating only useful reloads. For an extreme example where this helps a lot please see T3294. This should also fix #7198 Finally, this re-introduces the code to do Cmm rewriting using in `Dataflow` module (with the difference that we know operate on a whole block at a time). Signed-off-by: Michal Terepeta Reviewers: austin, bgamari, simonmar Reviewed By: simonmar Subscribers: kavon, rwbarton, thomie GHC Trac Issues: #7198 Differential Revision: https://phabricator.haskell.org/D3586 }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/7198#comment:15 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler