Get if the operand is a memory location (\ref kOpMem).

Use when there are no profile/version to check, it's just an error if one of the extensions is not present.

To support special built-ins that have a special qualifier that cannot be declared textually in a shader, like gl_Position. This lets the type of the

res = a + b

Get if the register is valid (either virtual or physical).

Set the operand signature (see \ref getSignature). Improper use of `setSignature()` can lead to hard-to-debug errors.

To be used only while the m_Mutex is locked. Used during defragmentation.