#10613: Mechanism for checking that we only enter single-entry thunks once -------------------------------------+------------------------------------- Reporter: bgamari | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: Other | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by nomeata):
A counting indirection sounds like the right kind of thing.
Looking a bit into this `IND_COUNTING` now; so I’ll go into “dumping notes into trac” mode, for the future benefit of me or whoever else continues. There is already a closure type `IND_PERM` which is not removed by the GC; our counting indirections requires the same behavior. So this is a good start, I guess. The following comments are observations from looking at every mention of `IND_PERM` in the code. * `Cmm.h` has macros to `ENTER` a closure, which shortcuts indirections without calling their entry code. This is not what we want for an `IND_COUNTING`; so we should use the `default` code there, to actually enter the counting closure. * Should the interpreter also count entries? I don’t see any reference to `ticky` in `Interpreter.c`, so probably not. * Should `rts/Stable.c` preserve `IND_COUNTING`? It does not preserve `IND_PERM`, so probably not. * Fun fact: tricky and profiling do currently not mix. As I plan to do this counting as part of ticky, this means I can ignore problems with profiling in the RTS (the closures still have to work, of course). * `scavenge_mark_stack` does nothing for `IND_PERM` with a comment I don’t fully understand. Will revisit. Weird. I only find lots of code that ''handles'' `IND_PERM`, but none that actually creates closures of that type. Is all that dead code, likely since 2010’s reimplementation of BLACHOLES by Simon Marlow? (changeset:5d52d9b/ghc) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10613#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler