[LLVMdev] Union type efforts and ComputeLinearIndex

[Andrew Lenharth]

On Sun, Aug 2, 2009 at 6:09 PM, Carter Cheng<carter_cheng at yahoo.com> wrote:
> I just looked over your diff and it would seem to me that additional changes would be needed to be done to some of the LLVM-IR -> DAG stuff to make things fully functional (this could be a bit of supposition on my part since I do not fully understand all of the code).

Code generation actually was supported.

See:
http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20090511/077465.html

Namely, look at the code in target data.

Andrew

>
> --- On Sun, 8/2/09, Andrew Lenharth <andrewl at lenharth.org> wrote:
>
>> From: Andrew Lenharth <andrewl at lenharth.org>
>> Subject: Re: [LLVMdev] Union type efforts and ComputeLinearIndex
>> To: "LLVM Developers Mailing List" <llvmdev at cs.uiuc.edu>
>> Date: Sunday, August 2, 2009, 3:55 PM
>> I posted an initial implementation
>> that would generate code correctly,
>> though I don't know that all optimization pass were safe
>> still.
>>
>> see:
>>
>> http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20090511/077443.html
>>
>> As far as I know, there isn't enough demand right now for
>> unions.
>> They are mainly useful for target-independent
>> front-ends.  I don't
>> have the time right now to push them, though they would be
>> useful for
>> my work, just not critical.
>>
>> Andrew
>>
>> On Sun, Aug 2, 2009 at 3:57 PM, Carter Cheng<carter_cheng at yahoo.com>
>> wrote:
>> > Hi,
>> >
>> > I really dont know I came rather late to the
>> discussion and some kind folks on this list gave me a few
>> links. I didnt see much mention of any controversy. Are
>> there issues still that need to be resolved?
>> >
>> > So far I am still quite the novice with LLVM internals
>> but looking over the code it looks like one could hack in
>> most of the required functionality up to the DAG building
>> stage. I am not sure if this would work so perhaps I could
>> get some opinions.
>> >
>> > My thoughts were as follows- introduce a new
>> CompositeType called union (possibly refactoring some stuff
>> into a common parent class from StructType).
>> >
>> > Recycle GEP (using RTTI) to handle UnionType field
>> lookups as well. Add type codes into bitreader/bitwriter
>> which would cope with the new union type. Add u { ... } into
>> the AsmParser.
>> >
>> > Revise some of the target classes to cope with the
>> unusual data layout and report back correct size for the
>> union type. Add support for DAG generation into the
>> DAGBuilder visitor class.
>> >
>> > I am just seeing this UnionType as a type of struct
>> where all the fields have the same offset and the UnionType
>> itself is as large as the largest member. I would speculate
>> that otherwise it behaves pretty much like a StructType- but
>> then again I am new to LLVM.
>> >
>> >
>> > --- On Sun, 8/2/09, Dan Gohman <gohman at apple.com>
>> wrote:
>> >
>> >> From: Dan Gohman <gohman at apple.com>
>> >> Subject: Re: [LLVMdev] Union type efforts and
>> ComputeLinearIndex
>> >> To: "LLVM Developers Mailing List" <llvmdev at cs.uiuc.edu>
>> >> Date: Sunday, August 2, 2009, 12:05 PM
>> >> Hello,
>> >>
>> >> My understanding of the discussions about union
>> types was
>> >> that
>> >> there was trouble working out how unions should
>> work. Have
>> >> the issues been resolved?  If so, could you post
>> a
>> >> summary?
>> >>
>> >> Thanks,
>> >>
>> >> Dan
>> >>
>> >> On Aug 2, 2009, at 7:45 AM, Carter Cheng wrote:
>> >>
>> >> > I am curious how the efforts were progressing
>> in
>> >> implementing a
>> >> > union type. I am will to try to contribute
>> somewhat to
>> >> this even
>> >> > though I am perhaps somewhat of a beginner
>> with
>> >> LLVM(so it might be
>> >> > nice to collaborate with someone). I had a
>> look at
>> >> some of the
>> >> > subsystems that would require changes though
>> I may
>> >> have missed some.
>> >> >
>> >> > I however have a few questions-
>> >> >
>> >> > 1) What is ComputeLinearIndex for
>> specifically? I
>> >> would expect that
>> >> > perhaps the RTTI stuff in there might need to
>> support
>> >> a new case for
>> >> > a union type.
>> >> >
>> >> > 2) The subsystems I have catalogued that
>> probably need
>> >> patching are
>> >> > AsmParser, BitCode(Reader/Writer), Target,
>> CodeGen and
>> >> some stuff in
>> >> > VMCore. Did I miss anything?
>> >> >
>> >> > Thanks in advance.
>> >> >
>> >> >
>> >> >
>> >> >
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