Nikolay Nikolov via fpc-pascal said on Mon, 12 Jun 2023 09:15:17 +0300
>On 6/12/23 04:44, Steve Litt via fpc-pascal wrote:
[snip]
>> So, subject to your guidance, I'm assuming FPC isn't optimized for
>> tail recursion. Is my assumption an accurate one?
>
>FPC supports tail recursion optimization, it is enabled at -O2
>optimization level for most CPUs, however your code isn't eligible for
>that optimization, because there's extra code, after the recursive
>invoke. If you change it like that:
>
>program recursion_hello;
>
>function nextt(num: int64): int64;
> begin
> writeln('Going deeper=> ', num);
> nextt := num;
> if (num > 0) then
> begin
> nextt(num - 1);
> end;
> end;
>
>begin
> nextt(1000000000);
>end.
>
>And if you compile with -O2 it works, without segfaulting (tested with
>FPC 3.2.2 on x86_64-linux).
Thanks Nickolay,
You're right about not assigning nextt below the call to nextt, and
about the -O2 argument. After learning from you about -O2 and
investigating further, I used {$OPTIMIZE tailrec}, which isn't quite the
same thing, but it worked beautifully. {$OPTIMIZE on} also enables tail
recursion and speeds things up about 10% of tailrec.
Thanks for your help.
SteveT
Steve Litt
Autumn 2022 featured book: Thriving in Tough Times
http://www.troubleshooters.com/bookstore/thrive.htm
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