[llvm] [VPlan] Run narrowInterleaveGroups during general VPlan optimizations. (PR #149706)

[David Sherwood via llvm-commits]

david-arm wrote:

I tried applying this patch to HEAD of LLVM (in combination with https://github.com/llvm/llvm-project/pull/149702) and I get this assert:

```
opt: llvm/lib/Transforms/Vectorize/VPlan.h:4092: unsigned int llvm::VPlan::getUF() const: Assertion `UFs.size() == 1 && "Expected a single UF"' failed.
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.
```

https://github.com/llvm/llvm-project/pull/149706