llvm dev - Aug 2018 - Passing arguments to var args function

Hey,

I am working on a new back-end,
in my back end, I require to pass every argument through a register when
calling a function, unless the argument is part of the ellipsis (...) and
then pass it through the stack, I've tried creating a CCCustom function to
analyze the operands when a function has var args, however, the information
whether the out val is fixed or not is not passed into the analyze
function, the code I'm talking about can be seen here:

https://github.com/llvm-mirror/llvm/blob/master/lib/CodeGen/CallingConvLower.cpp#L138

In line 144 the Fn is called, the Outs[i] contains the information required
for such thing because it contains the IsFixed flag.
Did anyone else come by such requirement? is there any other way anyone
could recommend handling such requirement?

Thanks in advance, Liad.
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Hi Liad,

On Wed, 8 Aug 2018 at 13:28, Liad Mordekoviz via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> Did anyone else come by such requirement? is there any other way anyone
could recommend handling such requirement?
Apple's calling convention on iOS does this. We have two separate
CC_Whatever definitions and then AArch64ISelLowering.cpp chooses which
one to use based on whether the argument is fixed or not (see line
3446 onwards).

Cheers.

Tim.

Hey Tim, thanks for the quick answer,
this looks exactly like what I was trying to achieve, I was hoping there
was something more clean,
I was wondering how the community would accept a change in the TD,
if the code at CallinvConvLower.cpp:138 would've passed the IsFixed flag to
the AssignFn then all those workarounds wouldn't be needed,
this example is only one of a few I can think of for expanding the
CallingConvention tablegen capabilities regarding this issue.

Thanks for the answer.

On Wed, Aug 8, 2018 at 4:21 PM, Tim Northover <t.p.northover at gmail.com>
wrote:
> Hi Liad,
>
> On Wed, 8 Aug 2018 at 13:28, Liad Mordekoviz via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
> > Did anyone else come by such requirement? is there any other way
anyone
> could recommend handling such requirement?
>
> Apple's calling convention on iOS does this. We have two separate
> CC_Whatever definitions and then AArch64ISelLowering.cpp chooses which
> one to use based on whether the argument is fixed or not (see line
> 3446 onwards).
>
> Cheers.
>
> Tim.
>
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