[PATCH] D117910: [RISCV] Add side-effect-free vsetvli intrinsics

[Jessica Clarke via Phabricator via llvm-commits]

jrtc27 added a comment.

In D117910#3266144 <https://reviews.llvm.org/D117910#3266144>, @frasercrmck wrote:

> In D117910#3266105 <https://reviews.llvm.org/D117910#3266105>, @kito-cheng wrote:
>
>> I would prefer use that to replace existing vsetvlimax and vsetvli once we verified that, I believe  vsetvl and vsetvlmax intrinsic should be no side effect on C/C++ language level.
>
> Yes I would have preferred that too. However I spoke with Craig offline and he told me that there are users which have now come to depend on the C/C++ vsetvli/vsetvlimax builtins having side effects. So I fear that ship may have sailed? I'd definitely be up for discussing a transition path but we'd need to assess the implications and any transition path.

The extensions were experimental until extremely recently (maybe V still is, even?); as someone not hugely involved in the vector work, if non-side-effecting intrinsics are significantly better than side-effecting ones then you should prioritise getting it right. The fallout is unfortunate but will be short-term, and we've never guaranteed any kind of stability for experimental extensions. Otherwise you'll have much more pain in the long run dealing with this legacy baggage.


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