Re: LLVM and PSEUDO_REG/PSEUDO_PHI

[Pekka Enberg <penberg@kernel.org>]

On Mon, Aug 29, 2011 at 12:45 PM, Pekka Enberg <penberg@kernel.org> wrote:
>> However, i'm not 100% sure that's sufficient. Is OP_CAST always zero-extend
>> or do we need to check for something specific here?

On Mon, Aug 29, 2011 at 11:32 PM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
> OP_CAST is always a zero-extend, OP_SCAST is a sign-extending one.
>
> (Of course, they may be *truncating* casts too, which don't need to
> generate any code on most architectures).
>
> OP_PTRCAST should act as OP_CAST.

OK, makes perfect sense. We don't support OP_SCAST or OP_PTRCAST yet
so those should be fine. I fixed OP_CAST like this:

https://github.com/penberg/sparse-llvm/commit/2dea6f7fb07cd18255cf1d73079638dc96bdd08b

So comparison operators should be OK now.

On Mon, Aug 29, 2011 at 11:32 PM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
> NOTE! The casting is dubious. We only have a single OP_FPCAST, for
> example, and that's just broken. Right now "OP_FPCAST" means that the
> *source* was a FP value. But if we cast *to* a FP value, it ends up
> showing up as OP_[S]CAST, which is just bogus. The FPCAST should be
> for any FP operation (to or from or both), and then the FPCAST logic
> would have to decide how it handles it.
>
> The FP support in general is pretty weak. The kernel doesn't do FP, I
> never really cared about it.

Good to know. I've added support for simple FP ops though and they
seem to be fine.

                        Pekka