[llvm] [LV] Use shl for (VFxUF * vscale) when creating minimum iter check. (PR #153495)

[David Sherwood via llvm-commits]

david-arm wrote:

> Could we also get the same thing if we instantiate the IRBuilder above with `IRBuilder<InstSimplifyFolder>`? I presume if it's limited to just this part of `createIterationCountCheck` then the IR should be well formed.

If I understand correctly we should probably be moving the IRBuilder to use the TargetFolder. See comment by @nikic on https://github.com/llvm/llvm-project/pull/150931. This is something I've considered doing in the loop vectoriser and vplan.

https://github.com/llvm/llvm-project/pull/153495