llvm dev - Sep 2017 - Adding a function type qualifier with particular keyword

Dear llvm developers,

For the purpose of a research project, I want to add a function type modifier as
an extension to LLVM that looks like

keyword void function(params1, 2, 3) {…}

to serve the purpose of tracking all registers that the function has touched. Is
there any documentation or previous examples relate to this feature?

Thank you very much
Garnet
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> For the purpose of a research project, I want to add a function type
> modifier as an extension to LLVM that looks like
Do you really need it to be part of the function's type? That brings
massive extra complexity, especially when C++ and its overloading
rules are involved.

Modifying a function's definition is a lot simpler. At the C/C++ level
you'd add a custom "__attribute__((whatever))", of which plenty
already exist. Since this records register usage Clang should probably
just add an LLVM function attribute saying the same thing. Then each
backend you want to support should look for that LLVM attribute, tot
up the registers just before emission and save them somewhere (a
separate section of the .o file?).

Basically you'd want some limited Clang support for forwarding a new
attribute, and a new LLVM backend pass in each target you supported to
save the correct info if needed.

Cheers.

Tim.

Thanks a lot for the reply! I looked into the function attributes description in
the references and I believe it’s a great approach, which hits the point
directly, but so far my mentor asks me to make it as a function type and it’s
for C. So I’m looking into both ways.
If I need add the function type modifier keyword, should it be in the Qualtype
class?

Thanks,
Garnet
> On Sep 23, 2017, at 3:30 PM, Tim Northover <t.p.northover at
gmail.com> wrote:
> 
>> For the purpose of a research project, I want to add a function type
>> modifier as an extension to LLVM that looks like
> 
> Do you really need it to be part of the function's type? That brings
> massive extra complexity, especially when C++ and its overloading
> rules are involved.
> 
> Modifying a function's definition is a lot simpler. At the C/C++ level
> you'd add a custom "__attribute__((whatever))", of which
plenty
> already exist. Since this records register usage Clang should probably
> just add an LLVM function attribute saying the same thing. Then each
> backend you want to support should look for that LLVM attribute, tot
> up the registers just before emission and save them somewhere (a
> separate section of the .o file?).
> 
> Basically you'd want some limited Clang support for forwarding a new
> attribute, and a new LLVM backend pass in each target you supported to
> save the correct info if needed.
> 
> Cheers.
> 
> Tim.