[llvm] [SandboxVec] Boilerplate (PR #107431)

[Mikael Holmén via llvm-commits]

mikaelholmen wrote:

> > And this crash goes away with [d14a600](https://github.com/llvm/llvm-project/commit/d14a600b1eb650f05fcd56a7b790e30f1f52e751) [SandboxIR] Implement BlockAddress (#107940)
> 
> @mikaelholmen Just curious how did you run into that issue?

We run some tests with randomized opt pass pipelines, and when sandbox-scalarizer was created we threw that pass into the mix as well.

https://github.com/llvm/llvm-project/pull/107431