I don't know how relevant this is; but this sounds like the sort of
optimization that pure functional programming allows for - that is, if
the compiler ever sees a call like asin(sin($x)), it might optimize
the code by just putting $x in there directly, and bypassing both the
sin and asin calls - but only because both sin and asin are pure
functions (i.e., they don't produce any side effects).
Don't get too hung up on that example.
If $x is 2*pi, asin(sin($x)) would return 0.0 and not 2*pi.
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