[PATCH] D31908: [AntiDepBreaker] Don't rename callee saved register restore instruction

[Matthias Braun via Phabricator via llvm-commits]

MatzeB added a comment.

In https://reviews.llvm.org/D31908#745037, @kparzysz wrote:

> In https://reviews.llvm.org/D31908#743873, @Carrot wrote:
>
> > In https://reviews.llvm.org/D31908#741341, @kparzysz wrote:
> >
> > > We add all callee saved registers as live-in on all paths from the restores to the exit, so this problem shouldn't affect us.  Actually the anti-dep breaker was the reason why we did it in the first place.
> >
> >
> > The second loop in function AggressiveAntiDepBreaker::StartBlock tries to do the work you described. Unfortunately it doesn't work with shrink wrapping. It says:
>
>
> This should be done in PEI, not in the anti-dependency breaker.  This is where the CSR registers get the concrete saving/restoring code.  Passes running afterwards should not need to know about what register is CSR or not (except pristine registers, but that's general enough).


Note that this is true for live-ins, however we don't explicitely safe live-out lists in the basic blocks. So for return blocks you have to take all CSR registers (depending on what you do with/without pristines). (See also https://reviews.llvm.org/D32464 where I partially rediscovered that fact).


https://reviews.llvm.org/D31908