[PATCH] D129013: [RISCV] Enable (scalable) vectorization by default

[Saleem Abdulrasool via Phabricator via llvm-commits]

compnerd added a comment.

In D129013#3712606 <https://reviews.llvm.org/D129013#3712606>, @reames wrote:

> @compnerd  Two points inspired by your response.
>
> 1. Are you saying that the uninitialized state is not guaranteed to have VS set to off?  This differs from my current understanding, and I don't see how this would follow from the wording in the vector spec.  If this is true, that's nasty and we should definitely clarify that.  Pointers to spec or discussion on this would be quite helpful.

Poorly worded on my side - I meant that it being defaulted to off, which means it is "unsupported" by default from the application PoV.

> 2. clang is inherently a cross compiler.  We can't ask question of the host environment (e.g. kernel version).  To my knowledge, this information is not available in any information we do have about the target platform.  Am I missing something here?

That is correct.  The check would need to be dynamic in that it must be part of the application.  Something like what Kito suggests with processing `/proc/cpuinfo`.  Longer term, it would be good to have the kernel actually check the riscv tag, but that leaves the older versions still in this state where things are easy to mis-configure.


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https://reviews.llvm.org/D129013