[Gelbpunkt]

The vclzlsbb and vctzlsbb instructions are available on POWER9 and newer with AltiVec enabled. They count the number of leading/trailing bytes in the vector with a LSB of zero.

Clang and GCC both define the vec_cntlz_lsbb and vec_cnttz_lsbb helpers for counting the leading/trailing bytes with LSB of zero in a vector. These then conditionally emit one or the other instruction, depending on endianess. For example, on big endian, vec_cntlz_lsbb emits vclzlsbb, while on little-endian, it emits vctzlsbb. We match that.

[rustbot]

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[folkertdev]

Hmm

rustc-LLVM ERROR: Cannot select: intrinsic %llvm.ppc.altivec.vclzlsbb

Some target feature not being set/used right?

[rustbot]

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

[Gelbpunkt]

Sorry! Fixed, it now works :)

[folkertdev]

Oh for posterity: we could use simd_ctlz and friends here semantically, but currently they are not interchangeable with the platform-specific intrinsics.