New primitive types?

[Michal Terepeta]

On Tue, Aug 1, 2017 at 8:08 PM Carter Schonwald <carter.schonwald at gmail.com>
wrote:
> One issue with packed fields is that on many architectures you can't
quite do subword reads or
> writes.  So it might not always be a win.

Could you give any examples?

Note that we're still going to do aligned read/writes, i.e., `Int32#`
would still be 4 bytes aligned, `Int16#` 2 bytes, etc. So we might
have "holes", e.g., `data Foo = Foo Int8# Int64#` would still waste 7
bytes (since `Int64#` should be 8 bytes aligned).

In the future, I'd also like to do some field reordering to avoid some
holes like that in cases like `Foo Int32# Int64# Int32#` (here it'd be
better if the in-memory layout was `Int64#` first and then the two
`Int32#`s)

> There's also the issue that c-- as it exists in ghc doesn't have any
notion of subword sized
> types.
>
> That said, I do support making word/int64/32 # types more first class /
built in.  (I hit some
> issues which tie into this topic in the process of working on my still in
progress safeword
> package. )
>
> Point being: I support improving what we have, but it's got a bit of
surface area.  Please let me
> know how I can help you dig into this though

Have a look at https://ghc.haskell.org/trac/ghc/ticket/13825 which
tracks the progress. The most recent diff is
https://phabricator.haskell.org/D3809

So far, most of this work is based on some unfinished code by Simon
Marlow to support storing constructor fields smaller than words.  I'm
currently mostly finishing/fixing it and splitting to smaller pieces.
Introducing more primitive stuff is the next step. (assuming everyone
is ok with this :)

Cheers,
Michal
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