[fpc-devel] Progress on pure functions

[J. Gareth Moreton]

Fixed that bug!  Also fixed a bug where the code analysis would get 
upset if you have "X mod Y" behind a "if (Y <> 0) then" check, and Y 
evaluates to zero.  I've attached a new test project to showcase this 
(and which revealed the aforementioned bug).  My branch also correctly 
replaces the function call with the number 12.

Kit

On 14/12/2022 01:17, J. Gareth Moreton via fpc-devel wrote:
> So there are bugs in my pure function code, specifically with the use 
> of current_procinfo - I didn't realise until now that the one relating 
> to the current function is actually freed after the body has been parsed.
>
> Ideally I would have gone the approach of reusing more of the 
> pass1_inline code and replacing the local variables and parameters 
> with temprefs, but data flow analysis doesn't yet work properly with 
> temprefs (and I haven't been able to work out why... basically if I 
> let them get included, their life information isn't filled in, so 
> dead-store elimination will strip ALL of the definitions, even the 
> ones that are very much needed).  I'll keep at it!
>
> Kit
>
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>
-------------- next part --------------
program pure2;
{$MODE OBJFPC}
{$COPERATORS ON}

function GCD(X, Y: Cardinal): Cardinal; pure;
  begin
    if Y = 0 then
      Result := X
    else
      Result := GCD(Y, X mod Y);
  end;

function Factorial(N: Cardinal): Cardinal; pure;
  var
    X: Integer;
  begin
    Result := 1;
    for X := N downto 2 do
      Result *= X;
  end;
  
var
  Output: Cardinal;
begin
  Output := GCD(84, Factorial(6)); { gcd(84, 720) = 12 }
  if Output <> 12 then
    begin
      WriteLn('Incorrect gcd - got ', Output, ' for gcd(84, 6!) but expected 12');
      Halt(1);
    end;
  
  WriteLn('ok');
end.