Re: Detailed algorithms on inline optimization

>> [True. Does anyone do that, inline the first few times though and
>> then punt to the normal routine? -John]


Muchnick (Advanced Compiler Design and Implementation) proposes that
the "normal" version of actually is inlined once or twice. This
reduces the number of recursive calls by a factor of about 2 ( or 3)
and gives you all the advantages of function inlining for each logical
recursion.


> Yeah, I was kind of impressed by the Verdix Ada compiler (years ago).
> A recursive Factorial function, something like:
>
> function Factorial (N : Natural) return Positive is
> begin
> if N = 0 then
> return 1;
> else
> return N * Factorial(N-1);
> end if;
> end Factorial;
> And then a call like "X := Factorial(7);" would compile into a "move
> 5040 into X" instruction. It had inlined 7 levels, and then
> constant-folded it. Factorial(8) didn't do that.
>
> I think 7 levels is excessive -- I'd choose 1, or maybe 2, because
> you're not normally going to be able to constant-fold the whole thing
> away.


You could do this by an analogous method to loop peeling. Inline
f(n). If the code expansion is within a limit, then inline f(n - 1)
and so on. For factorial, there will be no code expansion after the
first inline, and so it will continue until there are no calls left.


Jeremy Wright

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