[llvm] [LegalizeDAG] Freeze index when converting insert_elt/insert_subvector to load/store on stack. (PR #86850)

[Eli Friedman via llvm-commits]

efriedma-quic wrote:

In general, this seems like the right approach: we need the value to actually be masked to avoid UB.  (And we've drawn the line that poison exists in SelectionDAG.)

Some of the cases on x86 look like regressions as well... but they look like generic "freeze" optimization issues.

It looks like the original issue was reported against aarch64; should there be an aarch64 testcase?

https://github.com/llvm/llvm-project/pull/86850