[clang] [clang] Lower _BitInt(129+) to a different type in LLVM IR (PR #91364)

[John McCall via cfe-commits]

rjmccall wrote:

If you want to do things that way, you will need to (1) generalize CodeGenTypes with a new API that will return this load/store type when applicable and (2) look at all the places we call `ConvertTypeForMem`, `EmitToMemory`, and `EmitFromMemory` to make sure they do the right things.

https://github.com/llvm/llvm-project/pull/91364