llvm dev - Jul 2021 - MCAsmParser end-of-function API

On 2021-07-12, David Greene via llvm-dev wrote:
>AsmPrinter has an API emitFunctionBodyEnd that allows the target to emit
>whatever it needs at the end of a function.  I cannot seem to find a
>similar interface in MCAsmParser/AsmParser.  Did I miss it?  I have the
>need to emit some tail padding at the end of a function, before the
>func_end label.  I don't want to require users to emit the padding
>themselves when they hand-write asm.  I suppose I could override
>doBeforeLabelEmit and look for the func_end label but that sems hacky
>and brittle.  There's no guarantee the user would include such a label.
>
>                            -David
AsmParser::Run has the main workflow.
You may customize the actions with MCTargetAsmParser::onEndOfFile.

But may I ask why you need to emit something in (MC)AsmParser?
AsmPrinter appears to be the more appropriate place.

(Most targets only need to emit alignment at function start,
so they don't need to care about padding at function end.)

Fangrui Song <maskray at google.com> writes:
> But may I ask why you need to emit something in (MC)AsmParser?
> AsmPrinter appears to be the more appropriate place.
I am just learning the MC layer so perhaps I am indeed looking in the
wrong place.

I am thinking about the operation of llvm-mc, assembling a .s file into
an object file.  So I guess the ELF/Object streamer is the right place
to emit something, but it's not clear to me how it gets told we're at a
function end.
> (Most targets only need to emit alignment at function start,
> so they don't need to care about padding at function end.)
Yeah, there are a lot of assumptions in the MC layer that don't
necessarily hold for the target I'm working on.  :) I've been able to
work around most of them but the "pure assembler" flow is one I
haven't
figured out yet.

Thanks for your help!

                      -David