[llvm] Reland "RegisterCoalescer: Add implicit-def of super register when coalescing SUBREG_TO_REG" (PR #134408)

[Greg Bedwell via llvm-commits]

gregbedwell wrote:

Hello,
I've just raised #169485 which bisects to the reland of this in bb78728826ff57f3df859e79bfd857b5a175bb6d
Please can you take a look?

Thanks!

https://github.com/llvm/llvm-project/pull/134408