[llvm] [SandboxVectorizer] Fix out-of-bounds SeedBundle access (PR #215976)

[Anshil Gandhi via llvm-commits]

gandhi56 wrote:

> Thanks for the fix!
> 
> I just checked and if we run `bundle-vec(bottom-up),bundle-vec(top-down)` the assertion in BundleVec.cpp:593 that checks `assert(SeedSlice.size() >= 2 && "Bad slice!");` is also crashing. This is a different issue though, in this case it is a BottomUpVec bug, it should early exit if the aux vector is empty instead of asserting that it is non-empty.

I can take a look at it, unless you already have a fix ;)

https://github.com/llvm/llvm-project/pull/215976