Hi all, > There's no need to set the srt field of f_info if f_closure is the SRT, since > any reference to f_info in the code will give rise to a reference to f_closure > in the SRT corresponding to that code fragment. Does that make sense?
Makes sense, thanks. > The use of a closure as an SRT is really quite a nice optimisation actually. Agreed. > · If f is top level, and calls itself, there is no need to include a pointer > to f’s closure in f’s own SRT. > > I think this last point is the one you are asking, but I’m not certain. Close, I'm asking whether we should include a pointer to f in f's SRT (when f is recursive) when we're using f as the SRT (the [FUN] optimisation). I'll document the code I quoted in my original email with this info. Thanks, Ömer Simon Peyton Jones <simo...@microsoft.com>, 7 Oca 2020 Sal, 00:11 tarihinde şunu yazdı: > > Aha, great. Well at least [Note SRTs] should point back to the wiki page. > > > > Omer's question is referring specifically to the [FUN] optimisation described > in the Note. > > Hmm. So is he asking whether f’s SRT should have an entry for itself? No, > that’ would be silly! It would not lead to any more CAFs being reachable. > > > > Omer, maybe we are misunderstanding. But if so, can you cast your question > more precisely in terms of which lines of the wiki page or Note are you > asking about? And let’s make sure that the appropriate bit gets updated when > you’ve nailed the answer > > > > Simon > > > > From: Simon Marlow <marlo...@gmail.com> > Sent: 06 January 2020 18:17 > To: Simon Peyton Jones <simo...@microsoft.com> > Cc: Ömer Sinan Ağacan <omeraga...@gmail.com>; ghc-devs <ghc-devs@haskell.org> > Subject: Re: Code generation/SRT question > > > > We have: > > * wiki: > https://gitlab.haskell.org/ghc/ghc/wikis/commentary/rts/storage/gc/cafs > > * a huge Note in CmmBuildInfoTables: > https://gitlab.haskell.org/ghc/ghc/blob/master/compiler%2Fcmm%2FCmmBuildInfoTables.hs#L42 > > > > Maybe we need links to these from other places? > > > > Omer's question is referring specifically to the [FUN] optimisation described > in the Note. > > > > Cheers > > Simon > > > > On Mon, 6 Jan 2020 at 17:50, Simon Peyton Jones <simo...@microsoft.com> wrote: > > Omer, > > > > I think I’m not understanding all the details, but I have a clear “big > picture”. Simon can correct me if I’m wrong. > > > > · The info table for any closure (top-level or otherwise) has a > (possibly empty) Static Reference Table, SRT. > > · The SRT for an info table identifies the static top level closures > that the code for that info table mentions. (In principle the garbage > collector could parse the code! But it’s easier to find these references if > they in a dedicated table alongside the code.) > > · A top level closure is a CAF if it is born updatable. > > · A top level closure is CAFFY if it is a CAF, or mentions another > CAFFY closure. > > · An entry in the SRT can point > > o To a top-level updatable closure. This may now point into the dynamic > heap, and is what we want to keep alive. If the closure hasn’t been updated, > we should keep alive anything its SRT points to. > > o Directly to another SRT (or info table?) for a CAFFY top-level closure, > which is a bit faster if we know the thing is non-updatable. > > · If a function f calls a top-level function g, and g is CAFFY, then > f’s SRT should point to g’s closure or (if g is not a CAF) directly to its > SRT. > > · If f is top level, and calls itself, there is no need to include a > pointer to f’s closure in f’s own SRT. > > I think this last point is the one you are asking, but I’m not certain. > > All this should be written down somewhere, and perhaps is. But where? > > Simon > > > > From: ghc-devs <ghc-devs-boun...@haskell.org> On Behalf Of Simon Marlow > Sent: 06 January 2020 08:17 > To: Ömer Sinan Ağacan <omeraga...@gmail.com> > Cc: ghc-devs <ghc-devs@haskell.org> > Subject: Re: Code generation/SRT question > > > > There's no need to set the srt field of f_info if f_closure is the SRT, since > any reference to f_info in the code will give rise to a reference to > f_closure in the SRT corresponding to that code fragment. Does that make > sense? > > > > The use of a closure as an SRT is really quite a nice optimisation actually. > > > > Cheers > > Simon > > > > On Wed, 1 Jan 2020 at 09:35, Ömer Sinan Ağacan <omeraga...@gmail.com> wrote: > > Hi Simon, > > In Cmm if I have a recursive group of functions f and g, and I'm using f's > closure as the SRT for this group, should f's entry block's info table have > f_closure as its SRT? > > In Cmm syntax > > f_entry() { > { info_tbls: [... > (c1vn, > label: ... > rep: ... > srt: ??????] > stack_info: ... > } > {offset > c1vn: > ... > } > } > > Here should I have `f_closure` in the srt field? > > I'd expect yes, but looking at the current SRT code, in > CmmBuildInfoTables.updInfoSRTs, we have this: > > (newInfo, srtEntries) = case mapLookup (g_entry g) funSRTEnv of > > Nothing -> > -- if we don't add SRT entries to this closure, then we > -- want to set the srt field in its info table as usual > (info_tbl { cit_srt = mapLookup (g_entry g) srt_env }, []) > > Just srtEntries -> srtTrace "maybeStaticFun" (ppr res) > (info_tbl { cit_rep = new_rep }, res) > where res = [ CmmLabel lbl | SRTEntry lbl <- srtEntries ] > > Here we only update SRT field of the block if we're not adding SRT entries to > the function's closure, so in the example above, because we're using the > function as SRT (and adding SRT entries to its closure) SRT field of c1vn > won't > be updated. > > Am I missing anything? > > Thanks, > > Ömer _______________________________________________ ghc-devs mailing list ghc-devs@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs
