[llvm] change contents of ScalarEvolution from private to protected (PR #83052)

[Nikita Popov via llvm-commits]

nikic wrote:

You'll want to test this via unit tests in llvm/unittest/Analysis/ScalarEvolutionTest.cpp. I'd recommend to split this up into multiple PRs:

 * Add the AssumeLoopExits flag. Only check this inside loopIsFiniteByAssumption() and just add one test for it (because we already have coverage for the general functionality).
 * Add the GuaranteedUnreachable functionality. This will need a test for each place you check it. I think the GuaranteedUnreachable checks don't need to be guarded by AssumeLoopExits, this seems largely orthogonal.
 * Other changes done by Enzyme -- though it still looks like most of these are just Enzyme having outdated code and not actually changes we want to do. Only the PROP_PHI change looks obviously intentional.

https://github.com/llvm/llvm-project/pull/83052