Peeking into StgInfoTable in cmm

[Andrew Martin]

Thanks. The source code of ghc-heap has led me to what I was looking for.
That whole library hinges upon unpackClosure# (stg_unpackClosurezh), whose
implementation opens with the telling:

    info  = %GET_STD_INFO(UNTAG(closure));

In CmmParse.y, we find the implementation of GET_STD_INFO, and just a few
lines below is the INFO_TYPE macro. The combination of these (along with a
cmm implementation of UNTAG, which I am still unsure of exactly how to
accomplish) should do the trick.

On Wed, Feb 6, 2019 at 2:53 PM Matthew Pickering <
matthewtpickering at gmail.com> wrote:

> Unless I am misunderstanding you want something which works like ghc-heap.
>
> If so, perhaps these three files will be instructive?
>
>
> https://gitlab.haskell.org/ghc/ghc/blob/master/libraries/ghc-heap/GHC/Exts/Heap/InfoTable.hsc
>
> https://gitlab.haskell.org/ghc/ghc/blob/master/libraries/ghc-heap/GHC/Exts/Heap/InfoTableProf.hsc
>
> https://gitlab.haskell.org/ghc/ghc/blob/master/libraries/ghc-heap/GHC/Exts/Heap/Closures.hs#L25
>
> Cheers,
>
> Matt
>
> On Wed, Feb 6, 2019 at 7:29 PM Andrew Martin <andrew.thaddeus at gmail.com>
> wrote:
> >
> > For an optimization I’m implementing, I’m trying to write an inline
> primop that gives me lets me inspect the closure type of an arbitrary
> heap-allocated value. I’m close to figuring this out, and the FCode
> machinery is starting to make sense, but one thing eludes me. Starting from
> a StgHeader, I get the info table pointer. This is easy since it’s the
> first field in the struct. But next I have to deference the info table
> pointer and get the closure type. There are two fields at the beginning of
> an info table that may or may not be present. I don’t know how to figure
> out if they are present or not. I suspect that there is something I can get
> out of DynFlags that tells me this, but I can’t find anything else in the
> stg-to-cmm pass that reads from an info table.
> >
> > Sent from my iPhone
> > _______________________________________________
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>


-- 
-Andrew Thaddeus Martin
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