As we have already established/fixed in https://bugs.llvm.org/show_bug.cgi?id=42209 https://reviews.llvm.org/D63065 https://reviews.llvm.org/rL363522 the InstSimplify handling for @llvm.with.overflow ops with undefs is correct. Therefore if ConstantFolding produces different results, then it is wrong. This duplication of code hints at the need for some refactoring, but for now address the brokenness of ConstantFolding by copying the known-good handling from rL363522. Fixes https://bugs.llvm.org/show_bug.cgi?id=43188 llvm-svn: 370608
