InstCombine miscompilation

[saethlin]

Like #139866 this is from a fuzzer that generates Rust MIR: https://github.com/cbeuw/rustlantis.

I've tried to reduce the MIR, but I think there's a pretty complicated structure required because I can't get the MIR very small.
https://godbolt.org/z/G6qsWP57T

The program seems to miscompile starting at rustc -Zmir-opt-level=0 -Copt-level=1 -Cllvm-args=-opt-bisect-limit=159

[dtcxzyw]

Reproducer: https://alive2.llvm.org/ce/z/l2ArgJ

I've tried to reduce the MIR, but I think there's a pretty complicated structure required because I can't get the MIR very small.

FYI you can use https://github.com/dtcxzyw/llvm-ub-aware-interpreter?tab=readme-ov-file#automatic-ub-free-test-case-reduction-for-middle-end-miscompilation-bugs to reduce csmith/rustlantics-generated miscompilation reproducers.

[saethlin]

I'd love to use llubi but it doesn't compile against the tip of master or the llvm submodule in rust-lang/rust. So I'm not really sure how to get a working build on my system.

[dtcxzyw]

I'd love to use llubi but it doesn't compile against the tip of master or the llvm submodule in rust-lang/rust. So I'm not really sure how to get a working build on my system.

Fixed. It was broken by recent changes to ValueTracking: #142384