#8585: Loopification should omit stack check --------------------------------------------+------------------------------ Reporter: jstolarek | Owner: jstolarek Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.7 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Runtime performance bug | Unknown/Multiple Test Case: | Difficulty: Unknown Blocking: | Blocked By: | Related Tickets: --------------------------------------------+------------------------------ Changes (by jstolarek): * owner: => jstolarek Comment: Patrick, your patch validates successfully. I now see that it indeed places the loop header in the right place. What I don't fully understand in the code that generates the loop header: {{{ self_loop_info <- getSelfLoop case self_loop_info of Just (_, loop_header_id, _) | checkYield && isJust mb_stk_hwm -> emitLabel loop_header_id _otherwise -> return () }}} is the additional condition `checkYield && isJust mb_stk_hwm`. My understanding is that currently heap checks can be placed not only at the entry point to a function but also in the case alternatives, thunk entry points and few other places (according to Note [Heap checks]). We however want to emit loop header only before the heap check made when entering a function and I guess that `checkYield && isJust mb_stk_hwm` condition accomplishes just that. Is that correct? I wasn't able yet to fully convince myself that this always works. I'm not committing the fix until I am certain that it will always work the way we intend it to. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8585#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler