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19.14.2 Label Value Caveats

Jumping to a label defined in another function does not work. It can cause unpredictable results.

The best way to avoid this is to store label values only in automatic variables, or static variables whose names are declared within the function. Never pass them as arguments.

An optimization known as cloning generates multiple simplified variants of a function’s code, for use with specific fixed arguments. Using label values in certain ways, such as saving the address in one call to the function and using it again in another call, would make cloning give incorrect results. These functions must disable cloning.

Inlining calls to the function would also result in multiple copies of the code, each with its own value of the same label. Using the label in a computed goto is no problem, because the computed goto inhibits inlining. However, using the label value in some other way, such as an indication of where an error occurred, would be optimized wrong. These functions must disable inlining.

To prevent inlining or cloning of a function, specify __attribute__((__noinline__,__noclone__)) in its definition. See Attributes.

When a function uses a label value in a static variable initializer, that automatically prevents inlining or cloning the function.