[llvm] [SCCP] Support structure in freeze (PR #226537)

[Nikita Popov via llvm-commits]

nikic wrote:

>From the llvm-opt-benchmark diff, it looks like we currently fail to fold away a freeze of a constant: https://llvm.godbolt.org/z/r7nhThzzx This handles it as a side-effect, but this is really something that InstCombine should do. It looks like isGuaranteedNotToBeUndefOrPoison() has no support for constant structs.

https://github.com/llvm/llvm-project/pull/226537