[clang] [llvm] [RegisterCoalescer] Improve register allocation for return values by limiting rematerialization (PR #163047)

[guan jian via cfe-commits]

rez5427 wrote:

> From the motivation case, do you know why MachineCSE fails to optimize?

Machine CSE is before this register coalescer, maybe add a CSE after this remat will work.

https://github.com/llvm/llvm-project/pull/163047