[llvm-dev] RFC: PointerType should derive from Type rather than SequentialType

[Peter Collingbourne via llvm-dev]

Having heard no objections I went ahead and sent out a couple of patches to
implement this:

https://reviews.llvm.org/D26594
https://reviews.llvm.org/D26595

Peter

On Mon, Oct 31, 2016 at 1:48 PM, David Blaikie <dblaikie at gmail.com> wrote:

>
>
> On Mon, Oct 31, 2016 at 1:43 PM Peter Collingbourne <peter at pcc.me.uk>
> wrote:
>
>> Thanks David. I ended up trying this over the weekend (see
>> https://github.com/llvm-project/llvm-project/compare/
>> master...pcc:pointertype). It ended up being a net reduction in code
>> size so seems like a useful cleanup even independent of the typeless
>> pointer work, I'll see if I can send a patch to the list.
>>
>> FWIW I think this directly helps towards the migration because we would
>> have a clearer idea of where we are legitimately calling getElementType()
>> on arrays or vectors as opposed to the pointer uses which we want to remove.
>>
>
> Yep - seems helpful in that regard, for sure. Thanks for looking into
> it/working on it.
>
> (I don't feel sufficiently position to sign off on this - but at least
> from my perspective and that of the typeless pointer work, this seems good
> - I'll leave it to others to chime in for the broader buy-in here)
>
> - Dave
>
>
>>
>> Peter
>>
>> On Mon, Oct 31, 2016 at 11:24 AM, David Blaikie <dblaikie at gmail.com>
>> wrote:
>>
>> Seems pretty plausible to me - my only question would be whether it's
>> worth the churn to do this intermediate step before finishing off typeless
>> pointers (granted, I've stalled out on that for nearly a year, admittedly -
>> but good to have extra hands/incentives - there's still a fair bit of work
>> to do though, so understandable if it might not be useful to block progress
>> on other things to finish it off) - not sure how much work this would
>> produce as an intermediate step compared to progress towards the end goal
>> directly. Perhaps not much.
>>
>> - Dave
>>
>> On Sat, Oct 29, 2016 at 8:41 PM Peter Collingbourne via llvm-dev <
>> llvm-dev at lists.llvm.org> wrote:
>>
>> Hi all,
>>
>> An oddity that has existed for a long time in the IR is that PointerType
>> derives from SequentialType. Per subject I propose to make PointerType
>> derive from Type for a couple of reasons:
>>
>> - Values of type PointerType are unlike the other SequentialTypes (arrays
>> and vectors) in that they do not hold values of the element type. By moving
>> PointerType we can unify certain aspects of how the other SequentialTypes
>> are handled.
>> - PointerType will have no place in the SequentialType hierarchy once
>> pointee types are removed, so this is a necessary step towards removing
>> pointee types.
>>
>> Although this would slightly complicate GEP enumeration, this can be
>> handled at the API level and is also inevitable given the move to remove
>> pointee types.
>>
>> Specifically I want to change the API exposed by the GEP type iterator so
>> that each iterator can be in one of three states: unbounded array (i.e. the
>> existing PointerType state, which would represent the first "element" of
>> the GEP), bounded array (the existing ArrayType state) or struct (the
>> existing StructType state). In the former two cases clients would not have
>> access to the "underlying" type and would only be able to access the
>> "boundedness", the upper bound if any and the element type.
>>
>> Thanks,
>> --
>> --
>> Peter
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>>
>>
>>
>> --
>> --
>> Peter
>>
>


-- 
-- 
Peter
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