Re: Detailed algorithms on inline optimization

anton@mips.complang.tuwien.ac.at (Anton Ertl) writes:
>Kaz Kylheku <kkylheku@gmail.com> writes:
>>On 2010-01-25, Anton Ertl <anton@mips.complang.tuwien.ac.at> wrote:
>>> Chris Dodd <cdodd@acm.org> writes:
>>>>unsigned fib(unsigned n) { return n < 2 ? n : fib(n-2) + fib(n-1); }


[and the interesting code that gcc generates from that]


Here's another version:


unsigned fib(unsigned n)
{
    unsigned accum=0;
    for (; n>1; n--)
        accum += fib(n-2);
    return n+accum;
}


Apart from some differences in register and stack allocation, gcc
generates the same code for this as for the code above (including the
number of inlinings), so it's likely that gcc transforms the
doubly-recursive version above into something like this version.


I don't think that this can be expressed as a tail-recursive function
without helper function.


- anton
--
M. Anton Ertl
anton@mips.complang.tuwien.ac.at
http://www.complang.tuwien.ac.at/anton/

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