Question regarding __riscv_vsetvl mask/tail policy

[OMaghiarIMG]

Hello,

I was looking at an example in which we use _tu intrinsics:

The first __riscv_vsetvl translates to vsetvli ta,mu, then __riscv_vle32 adds another vsetvl to set the policy to tu,ma. Would it be possible to have a single vsetvl with tu,ma since the beginning?

Would having _mu/_tu variants of the __riscv_vsetvl intrinsic make sense?

[zhongjuzhe]

No, I don't think we need to add _mu/_tu variants of __riscv_vsetvl intrinsic.

__riscv_vsetvl intrinsic is defined as any tail policy and any mask policy.

Compiler should be able to well optimize vsetvlis.

Compiler can well handle your case, no redundant vsetvli:

https://godbolt.org/z/EY44M1nsa

[OMaghiarIMG]

Thanks, yes this issue was present on my local clang16, didn't look at gcc. Here's an example with a mask setting instruction, gcc sets tu,ma since the beginning, clang does a switch to ta and then back to tu. https://compiler-explorer.com/z/TE5fzEh7j

[zhongjuzhe]

I think you should try trunk Clang:

https://compiler-explorer.com/z/ave8TdPM5

The intrinsic has significantly changed recently and will be frozen soon. Clang16 didn't support the latest rvv intrinsics.