2afe678f0a
We currently elide memcpys for readonly nocapture noalias arguments. noalias is checked to make sure that there are no other ways to write the memory, e.g. through a different argument or an escaped pointer. In addition to the current noalias check, also query alias analysis, in case it can prove that modification is not possible through other means. This fixes the problem reported in https://discourse.llvm.org/t/problem-about-memcpy-elimination/81121.