[PATCH] D87399: Revert "[InstCombine] erase instructions leading up to unreachable"

[Chandler Carruth via Phabricator via llvm-commits]

chandlerc added a comment.

In D87399#2263996 <https://reviews.llvm.org/D87399#2263996>, @nikic wrote:

>> however, a volatile access can abort a program. In that case, an unreachable instruction after it is not reachable. So undefined behavior does not happen, and the volatile access cannot be removed.
>
> As already explained in the referenced revision, this is not correct. Volatile accesses are not permitted to trap. LangRef is unambiguous on this point:
>
>> The compiler may assume execution will continue after a volatile operation, so operations which modify memory or may have undefined behavior can be hoisted past a volatile operation.

I'll follow up on this point in the original review thread for continuity.


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https://reviews.llvm.org/D87399