[llvm] [AMDGPU] Add IR LiveReg type-based optimization (PR #66838)

[Jeffrey Byrnes via llvm-commits]

jrbyrnes wrote:

I've reopened for the reland,  the latest fixes the use-after-free / memory issues in https://github.com/llvm/llvm-project/pull/97138. 

Since visitLoadInst deletes dead loads, optimizeLiveType may try to analyze freed memory. Simply deferring the deletion until post-loop doesn't work as the loads marked for removal may be part of a subsequently coerced chain. In order to integrate the loops, these interactions will need to be handled, which is left as a TODO.

https://github.com/llvm/llvm-project/pull/66838