Function get_constraint 

fn get_constraint<'entries, 'table>(
    operand: &'entries Operand,
    ctrl_typevar: Option<&TypeVar>,
    type_sets: &'table mut UniqueTable<'entries, TypeSet>,
) -> String

Get the value type constraint for an SSA value operand, where ctrl_typevar is the controlling type variable.

Each operand constraint is represented as a string, one of:

• Concrete(vt), where vt is a value type name.
• Free(idx) where idx is an index into type_sets.
• Same, Lane, AsTruthy for controlling typevar-derived constraints.