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

[Kai Luo via llvm-commits]

bzEq wrote:

> This happens with optimized IR too:

A more simplified version

```
@bytes1 = external local_unnamed_addr global ptr

define noundef i8 @foo() local_unnamed_addr #0 {
  store i32 42, ptr @bytes1, align 8
  ret i8 42
}
```

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