llvm-project

7b053679 - [ADT] Fix specialization of ValueIsPresent for PointerUnion (#121847)

[ADT] Fix specialization of ValueIsPresent for PointerUnion (#121847) Two instances of `PointerUnion` with different active members and null value compare unequal. Currently, this results in counterintuitive behavior when using functions from `Casting.h`, e.g.: ```C++ PointerUnion<int *, float *> U; // U = (int *)nullptr; dyn_cast<int *>(U); // Aborts dyn_cast<float *>(U); // Aborts U = (float *)nullptr; dyn_cast<int *>(U); // OK dyn_cast<float *>(U); // OK ``` `dyn_cast` should abort in all cases because the argument is null. Currently, it aborts only if the first member is active. This happens because the partial template specialization of `ValueIsPresent` for nullable types compares the union with a union constructed from nullptr, and the two unions compare equal only if their active members are the same. This patch changed the specialization of `ValueIsPresent` for nullable types to make `isPresent()` return false for all possible null values of a PointerUnion, and fixes two places where the old behavior was exploited. Pull Request: https://github.com/llvm/llvm-project/pull/121847