[llvm] [SLP][REVEC] Ignore UserTreeIndex if it is empty. (PR #131993)

[Paul Kirth via llvm-commits]

ilovepi wrote:

> We're seeing what appears to be an MSan test failure after this patch on Linux Aarch64 bots. The patch seems pretty benign to me, but this is the only change in the blame list. Any idea about why that could be?
> 
> CC: @vitalybuka in case he knows of something else that could be happening.
> 
> Bot link: https://ci.chromium.org/ui/p/fuchsia/builders/toolchain.ci/clang-linux-arm64/b8719911097381318689/infra

Ugh, sorry for the noise. A team member pointed out that something changed in our infra around that time, so indeed its unrelated to your patch. Apologies.

https://github.com/llvm/llvm-project/pull/131993