llvm dev - Jul 2008 - [LLVMdev] Plans considering first class structs and multiple return values

Hello,

The basic infrastructure is in place. You can create first-class
structs/arrays using sequences of insertvalue.

For example, this:

   %t0 = insertvalue { i32, i32 } undef, i32 %a, 0
   %t1 = insertvalue { i32, i32 } %t0,   i32 %b, 1

creates the value with %a and %b as member values. Other ways to
produce aggregate values are loads, function arguments, function
return values, and literal constants.

It's all pretty new and hasn't seen much exposure, so one of
the things it needs right now is for people to try it out and
see how it goes.

There is work yet to be done in several of the optimization
components. And codegen can't yet handle aggregate return
values larger than what fits in designated return value
registers. I'm planning to have LLVM auto-upgrade the
multiple-return-value constructs that exist in LLVM 2.3,
which should give it quite a bit of exposure, though that
probably won't happen for a while.

And while I'm here, I want to emphasize that this feature does
not completely solve the problem of C-oriented ABI-compliant
passing/returning of structs. That's a complicated problem, and
unfortunately it is beyond the immediate scope of this feature.

Dan

On Jul 2, 2008, at 3:00 PM, Marc de Kruijf wrote:
> Hi, I'm really interested in this effort.  What is its status?  Is any
> of it in svn yet?  (I only see the insert/extract value instructions
> so far... nothing w.r.t. creating a first-class struct/array).  Can I
> do anything to help?
>
> Marc

> For example, this:
>
>   %t0 = insertvalue { i32, i32 } undef, i32 %a, 0
>   %t1 = insertvalue { i32, i32 } %t0,   i32 %b, 1
>
> creates the value with %a and %b as member values.
Is there anyway to do it using the C++ API?  It seems I need an
instance of the aggregate type to pass into InsertValueInst::Create().
 What is the API equivalent of "undef"?

Marc

On Wed, Jul 2, 2008 at 6:54 PM, Dan Gohman <gohman at apple.com>
wrote:
> Hello,
>
> The basic infrastructure is in place. You can create first-class
> structs/arrays using sequences of insertvalue.
>
> For example, this:
>
>   %t0 = insertvalue { i32, i32 } undef, i32 %a, 0
>   %t1 = insertvalue { i32, i32 } %t0,   i32 %b, 1
>
> creates the value with %a and %b as member values. Other ways to
> produce aggregate values are loads, function arguments, function
> return values, and literal constants.
>
> It's all pretty new and hasn't seen much exposure, so one of
> the things it needs right now is for people to try it out and
> see how it goes.
>
> There is work yet to be done in several of the optimization
> components. And codegen can't yet handle aggregate return
> values larger than what fits in designated return value
> registers. I'm planning to have LLVM auto-upgrade the
> multiple-return-value constructs that exist in LLVM 2.3,
> which should give it quite a bit of exposure, though that
> probably won't happen for a while.
>
> And while I'm here, I want to emphasize that this feature does
> not completely solve the problem of C-oriented ABI-compliant
> passing/returning of structs. That's a complicated problem, and
> unfortunately it is beyond the immediate scope of this feature.
>
> Dan
>
> On Jul 2, 2008, at 3:00 PM, Marc de Kruijf wrote:
>
>> Hi, I'm really interested in this effort.  What is its status?  Is
any
>> of it in svn yet?  (I only see the insert/extract value instructions
>> so far... nothing w.r.t. creating a first-class struct/array).  Can I
>> do anything to help?
>>
>> Marc
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>

On Wed, Jul 2, 2008 at 6:37 PM, Marc de Kruijf <dekruijf at cs.wisc.edu>
wrote:
>  What is the API equivalent of "undef"?
UndefValue::get(const Type*), in Constants.h.

-Eli

Hi Marc,

there a few examples of this in the code, have look at BuildSubAggregate in
lib/Analysis/ValueTracking.cpp for example (there's quite some code around
it
and it's recursive, which doesn't make this the best example, but it
should
help).

The interesting parts look something like this:

Value *Undef = UndefValue::get(IndexedType);
Value *T0 = lvm::InsertValueInst::Create(To, V, Idxs.begin(),
																				 Idxs.end(), "tmp", InsertBefore);
Value *T1 = lvm::InsertValueInst::Create(To, V, Idxs2.begin(),
																				 Idxs2.end(), "tmp", InsertBefore);

Gr.

Matthijs
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