[llvm] [AMDGPU] Avoid put implicit_def into bundle that break reg's liveness (PR #142563)

[Jay Foad via llvm-commits]

jayfoad wrote:

> Since the def & use of BUNDLE inst is hand written in different backends, it requires us to change all backend's BUNDLE creation logic if we want to use method 1.

No, the generic code in `finalizeBundle` does this. It looks at the operands of the instructions in the bundle, and adds corresponding operands to the BUNDLE instruction.

The idea is that the operands on the bundle should have the same overall effect as the sequence of instructions-and-operands inside the bundle. This gets a complicated when a def operand of an instruction early in the bundle gets partially redefined by a def of an overlapping register later in the bundle.

https://github.com/llvm/llvm-project/pull/142563