llvm dev - Jun 2017 - Function with multi return path?

Hi Reid,

I'm aware of the invoke instruction and landingpad. But it's too heavy
weight for control flow. It's quite expensive to take the exceptional path
in C++.

What I want is a more lightweight approach, to pass the return address to
the callee, and let the callee jump to that address directly.
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On 2 Jun 2017, at 03:38, TONGARI J via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> I'm aware of the invoke instruction and landingpad. But it's too
heavy
> weight for control flow. It's quite expensive to take the exceptional
path
> in C++.
> 
> What I want is a more lightweight approach, to pass the return address to
> the callee, and let the callee jump to that address directly.
The best way of implementing this is likely to be to use a custom calling
convention along with invoke.  The invoke instruction will handle the semantics
correctly in the IR, but you’ll need to modify the back end to understand that
it should generate the call site differently and not emit unwind tables.

David

2017-06-02 19:51 GMT+08:00 David Chisnall <David.Chisnall at
cl.cam.ac.uk>:
> On 2 Jun 2017, at 03:38, TONGARI J via llvm-dev <llvm-dev at
lists.llvm.org>
> wrote:
> >
> > I'm aware of the invoke instruction and landingpad. But it's
too heavy
> > weight for control flow. It's quite expensive to take the
exceptional
> path
> > in C++.
> >
> > What I want is a more lightweight approach, to pass the return address
to
> > the callee, and let the callee jump to that address directly.
>
> The best way of implementing this is likely to be to use a custom calling
> convention along with invoke.  The invoke instruction will handle the
> semantics correctly in the IR, but you’ll need to modify the back end to
> understand that it should generate the call site differently and not emit
> unwind tables.
>
A custom calling convention doesn't suffice, there could be more than one
alternate paths. And invoke instruction is also not general enough.
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