This reverts commit 4e413e16216d0c94ada2171f3c59e0a85f4fa4b6,
which landed almost 10 months ago under premise that the original behavior
didn't match reality and was breaking users, even though it was correct as per
the LangRef. But the LangRef change still hasn't appeared, which might suggest
that the affected parties aren't really worried about this problem.
Please refer to disscussion in:
- https://reviews.llvm.org/D87399 (Revert "[InstCombine] erase instructions leading up to unreachable")
- https://reviews.llvm.org/D53184 ([LangRef] Clarify semantics of volatile operations.)
- https://reviews.llvm.org/D87149 ([InstCombine] erase instructions leading up to unreachable)
Perhaps, this isn't destined to land, but merely to nudge towards further disscussion and a proper resolution.