[llvm-dev] Support for out-of-tree backend passes?

[Nemanja Ivanovic via llvm-dev]

I think another source of difficulty is specifying what representation the
pass runs on. Don't forget that the back end lowers LLVM IR to SDAG, then
the SDAG is selected, converted into SSA MIR, then RA and rewriting happens
to take it out of SSA and finally it lowers to the MC layer. It would be
ambiguous to invoke
llc -my-pass
unless we are restricting the passes to IR->IR ones, restricting it to
pre-codegenprep and generally imposing the same requirements on the passes
as exist in the middle end.

On Sat., Mar. 2, 2019, 11:15 p.m. William Woodruff via llvm-dev, <
llvm-dev at lists.llvm.org> wrote:

> On Sat, Mar 02, 2019 at 07:34:50PM -0800, Tim Northover wrote:
>
> > The biggest difference and problem I see would be building the thing,
> > since the target's headers are going to be needed, but they're
> > private. That means they're not shipped with LLVM so you'd need the
> > source (and an active build directory for the TableGenerated files,
> > lib/Target/XYZ/XYZGen*.inc), which might make the whole project moot
> > (depending on your reasons for doing it).
>
> Yeah, that's a problem. My particular use case is mostly
> target-independent, so I hadn't thought about that.
>
> Well, I'll do some fiddling and see if anything sticks.
> Thanks for the response!
>
> William
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