[llvm-branch-commits] [llvm] RegAlloc: Fix failure on undef use when all registers are reserved (PR #119647)

[Matt Arsenault via llvm-branch-commits]

arsenm wrote:

### Merge activity

* **Dec 15, 8:41 PM EST**: A user started a stack merge that includes this pull request via [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/119647).


https://github.com/llvm/llvm-project/pull/119647