fhahn added a comment.
In D65776#1615834 <https://reviews.llvm.org/D65776#1615834>, @Meinersbur wrote:
> Mmmh, I would have expected this to work the same way as `vectorize_width`.
> According to the docs:
>
> > The following example implicitly enables vectorization and interleaving by
> > specifying a vector width and interleaving count:
> > `#pragma clang loop vectorize_width(2) interleave_count(2)`
> > `for(...) {`
> > ` ...`
> > `}`
>
> However, `vectorize_width` does not automatically set
> `llvm.loop.vectorize.enable`. Neither does `llvm.loop.vectorize.width` > 1
> imply `LoopVectorizeHints::getForce()`. At some places they are checked
> together, such as `LoopVectorizeHints::allowReordering()`. Other places,
> notably `LoopVectorizationCostModel::selectVectorizationFactor()`, only
> queries `getForce()`. That is, `vectorize_width(2)` does not implicitly force
> vectorization in practice.
The current behavior with respect to vectorize_width seems a bit
counterintuitive. The docs say `vectorize_width implicitly enables
vectorization`, I would expect it to behave as if `vectorize(enable)` was also
passed. There's also a PR about that mismatch:
https://bugs.llvm.org/show_bug.cgi?id=27643
IMO it would make sense to have the more specific pragmas imply
vectorize(enable) here (or update the docs accordingly).
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