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5.8.2 Semi-Inline Expansion

Python supports semi-inline functions. Semi-inline expansion shares a single copy of a function across all the calls in a component by converting the inline expansion into a local function (see local-call.) This takes up less space when there are multiple calls, but also provides less opportunity for context dependent optimization. When there is only one call, the result is identical to normal inline expansion. Semi-inline expansion is done when the space optimization quality is 0, and the function has been declared extensions:maybe-inline.

This mechanism of inline expansion combined with local call also allows recursive functions to be inline expanded. If a recursive function is declared inline, calls will actually be compiled semi-inline. Although recursive functions are often so complex that there is little advantage to semi-inline expansion, it can still be useful in the same sort of cases where normal inline expansion is especially advantageous, i.e. functions where the calling context can help a lot.