Usually, but it is compiler dependent. Optimization is not guaranteed by the language specification. Variables declared as constant, are not the same thing as literal values in expressions.
The ability to inline code a multi word constant in order to optimize some statement, depends on how that constant is used in the statement.
Inlining single word constants is so easy that it's been done almost since the beginning of C compilers. That's because it usually has processor support. That would apply to either declared or literal values of the same word size as the processor in question.