[llvm-commits] [patch] Add a pass for duplicating indirectbr at the IL level

[Rafael Ávila de Espíndola]

> How do you define "works"?

Prouduces better code?

 > You haven't provided a good explanation
> for why the LLVM IR level is a better place for tail duplication than
> the MI level.

I provide an example in the very first email.

> Have you come up with a solution for the problem that
> you can't judge the code size of IR instructions?  I'd like to see a
> more detailed design proposal.

A similar problem exists with the early tail dup at the IL level too.

> I realize, of course, that I haven't yet provided any details of my
> work, either.  I've got a bunch more pressing things to do this week,
> but I'll try to make progress soon.

BTW, this is the second time you mention this pass to oppose to patch
I am working on. The previous time it so happened that my patch
helped both webkit and firefox and it has already been committed.

I always try to send work in progress patches to collect feedback.
Would you mind doing the same? If reading your patch I realize it
is clearly better, I would be more than happy finish the
missing parts. I would also be happy to benchmark the two.

>> Sorry, the question was more on the "how to duplicate", not "where
>> to duplicate". If previous optimizations gives us
>>
>> zed: ... br i1 %foo, %indirectgoto, %bar
>>
>> and you decide that the indirect goto should be duplicated to zed,
>> how do you do it?
>
> If you want to duplicate back "zed", you need to duplicate all the
> code between that point and the indirect branch.

Sorry, what is "that point"? the br instruction? The indirectgoto
above is the bb created by clang with the indirectbr.

Cheers,
Rafael