Safe code (ui/issues/issue-69225-SCEVAddExpr-wrap-flag.rs) miscompiles under llvm9 + codegen-units=1

[the8472]

---- [ui] ui/issues/issue-69225-SCEVAddExpr-wrap-flag.rs stdout ----

error: error pattern ' index out of bounds: the len is 0 but the index is 16777216' not found!
status: signal: 11
command: "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/issues/issue-69225-SCEVAddExpr-wrap-flag/a"

Current reproducer: #81945

Original issue: #69225. According to #69225 (comment) the testcase originally did work fine for any number of codegen units. Seems like a regression.

[Stupremee]

Assigning P-medium as discussed as part of the Prioritization Working Group procedure and removing I-prioritize.

[nagisa]

I believe we use unpatched/upstream LLVM in for the llvm-9 CI jobs, which would make this technically a not-a-rustc-issue, given that the original fix relied on patching LLVM (10 &later).

Conceptually it'd be upto the distribution maintainers to apply corresponding patches to the LLVM they ship.

[nikic]

Right, I don't think there's anything we can really do here, as it's a bug in external LLVM. I think simply adding a min-llvm-version to the test would be fine.