[PATCH] D72492: GlobalISel: Implement lower for G_BITCAST

Fri Jan 10 10:50:40 PST 2020

aemerson added a comment.

In D72492#1814675 <https://reviews.llvm.org/D72492#1814675>, @arsenm wrote:

> In D72492#1814575 <https://reviews.llvm.org/D72492#1814575>, @arsenm wrote:
>
> > In D72492#1814528 <https://reviews.llvm.org/D72492#1814528>, @aemerson wrote:
> >
> > > On AArch64 we also use bitcast to convert from <n x p0> to <n x s64> types.
> >
> >
> > I thought that was illegal. It’s not legal in IR
>
>
> I think this is a verifier bug. You're not allowed to bitcast between scalar pointers and scalars, so allowing it for vectors doesn't make much sense.  I think allowing this is potentially problematic for non-integral pointers since it makes it easy to accidentally launder away the pointerness

We don't have an alternative way to easily convert between them though. Unless G_PTRTOINT is also allowed to take vectors of pointers.

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https://reviews.llvm.org/D72492