[clang] [clang] Better bitfield access units (PR #65742)

[Nathan Sidwell via cfe-commits]

urnathan wrote:


> Also, please have a look at the existing `-ffine-grained-bitfield-accesses` flag and the discussions around it and IPO.

That flag's behaviour is unchanged here -- it continues to not merge access units. My contention here is that (a) merging units can be advantageous, but (b) the existing algorithm has some deficiencies.

https://github.com/llvm/llvm-project/pull/65742