[Nouveau] [Bug 90887] PhiMovesPass in register allocator broken

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=90887

--- Comment #33 from Ilia Mirkin <imirkin at alum.mit.edu> ---
(In reply to jr from comment #32)
> (In reply to Ilia Mirkin from comment #31)
> > Really if I could understand wtf the needNewElseBlock logic was trying to
> > do, and could construct a test shader to hit this in *regular* scenarios,
> > not just the lowered output of TXL, that would make me a lot more
> > comfortable with any approach that we pick.
> 
> Looking at the TGSI->IR translation I'd guess that needNewElseBlock is
> trying to detect the edge from the 'bare' unconditional jump in an if
> without else, seemingly because adding the new moves is not allowed (though
> I'm not sure why). At least it seems to be the only construct creating a
> graph satisfying the condition, AFAICT.

Well, in general you can't add work if you have a critical edge -- if an block
has multiple outgoing edges, then you can't put the work into that block. If a
block has multiple incoming edges, then you can't leave the work in that block,
so you have to create a separate block to put work that you want done on that
specific block transition.

However here it's looking for something much more specific.

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