[Bug][move-compiler-v2] Mutable borrow with copy on RHS of equality check

[zzjas]

🐛 Bug

Compiler V1 can compile the following program but compiler V2 will give an error.

To reproduce

Code snippet to reproduce

module 0xCAFE::Module0 {
    public fun function2(var4: u8): bool {
        (&mut (var4) != &mut (copy var4))
    }
}

Stack trace/error message V2 gives:

error: cannot copy local `var4` which is still mutably borrowed
  ┌─ ~/debug_package/sources/repro.move:3:30
  │
3 │         (&mut (var4) != &mut (copy var4))
  │         ---------------------^^^^^^^^^^^-
  │         ││                   │
  │         ││                   copied here
  │         │previous mutable local borrow
  │         │used by freeze
  │         conflicting reference used here

[zzjas]

A variant from #13952 might be related to this:

If we compile the following code with V2:

module 0xCAFE::Module0 {
    public fun function5(var21: bool, var23: bool) {
        let var67 =  (&(var21) != &((var21 || var23)));
    }
}

The bytecode verifier will give MOVELOC_EXISTS_BORROW_ERROR (currently marked as known issue).

If the order of operands is flipped, i.e.:

module 0xCAFE::Module0 {
    public fun function5(var21: bool, var23: bool) {
        let var67 =  (&((var21 || var23)) != &(var21));
    }
}

It will be compiled successfully.

Both can be compiled by V1 successfully.