This patch expands the expressive capability of the casting utilities in LLVM by introducing several levels of configurability. By creating modular CastInfo classes we can enable projects like MLIR that need more fine-grained control over how a cast is actually performed to retain that control, while making it easy to express the easy cases (like a checked pointer to pointer cast).
The current implementation of Casting.h doesn't make it clear where the entry points for customizing the cast behavior are, so part of the motivation for this patch is adding that documentation. Another part of the motivation is to support using LLVM RTTI with a wider set of use cases, such as nullable value to value casts, or pointer to value casts (as in MLIR).
Reviewed By: lattner, rriddle
Differential Revision: https://reviews.llvm.org/D123901
f156b51aec