The instruction "or dword ptr [rbx+0x48], 0xffffffff" is wrongly reported as uninitialized read by the inspector. (E.g. used in MSVCP140.DLL)
Obviously false positive, as the result does not depend on the previous memory content at all.
The other way around, e.g. "and dword ptr [rbx+0x4c], 0x0", is not flagged as a read.
For more complete information about compiler optimizations, see our Optimization Notice.