[llvm] [MemoryBuiltins] Cache the result of ObjectOffsetSizeVisitor::visit. #64796 (PR #65326)

[Nikita Popov via llvm-commits]

nikic wrote:

getObjectSize() is almost always called on root instructions (identified objects like allocas, globals) -- actually using it with objectsize intrinsics is rare. I expect this is the additional overhead of the map, not the extra iteration.

https://github.com/llvm/llvm-project/pull/65326