Hi all,
!1381/#16893: inline unsafeCoerce# in CorePrep
The problem with !1381 is that it reveals a coercion accepted by CoreLint but rejected by an assertion later in the compilation. The coercion casts an Int# to Int64#, which is fine on a 64-bit system. One way to fix this is by fixing #17026, but as explained in the issue it's too much work and it'll either require huge amount of work (if we implement some kind of Type/TyCon caching) or make everything slower (if we make top-level intPrimTy/intPrimTyCon which are currently constants, functions).
#17041: coercion safety in STG Lint
This basically asks for a type checker that works on PrimReps instead of Types. I was too busy with #9718/!1304 and #17088 so couldn't make progress here. Perhaps I can work on this at MuniHac.
!1552: tidy up linting on unsafe coercions
I'll address your comments and test this more. My main concern (and the reason why I added "DO NOT MERGE") was that I wasn't 100% sure that this change is sound (though I don't remember what I was concerned about specifically). I'll try to test this more on my desktop (where I can more efficiently make release builds and test) when I'm back home.
#16964: definition of Int#
The part related to GHC internals is moved to #17026. Regarding definition of Int#, I'm not sure what to do about this,
#17026: definition of IntRep
Simon argues that if we keep Int and Int# distinct types (rather than synonyms to Int32/Int64 and Int32#/Int64# depending on platform word size, this is discussed in #16964) then we should keep RuntimeReps for them distinct too. I think this is mostly fine but a problem with this that blocked !1381 is IntRep and Int64Rep are not equal (according to the Eq instance) on a 64-bit system so a simple code that checks whether two types are represented the same fails. If we keep IntRep/WordRep then I think we should remove the Eq instance of PrimRep and and provide a `primRepEq :: PlatformWordSize -> PrimRep -> PrimRep -> Eq` for checking whether types are represented the same on the target platform (or maybe name it `primRepCoercible`). So in summary; I think I'll make progress in this order: - Read the changes in !1552, test it more. - If merged then !1381 will be unblocked, merge it. - Remove Eq instance of PrimRep, implement primRepEq (or primRepCoercible) that takes target platform size as argument. Use this in coercion checks. - This also unblocks !1381, merge it - Implement type checker in StgLint that works on PrimReps (instead of on actual types). I'm not sure about how to proceed in #16964. I'm inclined to just document the status quo more accurately, but apparently there's also a MR that's supposed to improve/fix it (!1102), though I'm having trouble seeing how it is even related. Ömer On 3.09.2019 00:45, Simon Peyton Jones wrote:
Omer, Ben
There’s a little cluster of tickets that it’d be really good to nail.
* !1381/#16893: inline unsafeCoerce# in CorePrep * #17041: coercion safety in STG Lint * !1552: tidy up linting on unsafe coercions * #16964: definition of Int# * #17026: definition of IntRep
They are all somehow tied up together. Can we kill them off together, soon? I have left comments...
Simon