How does the Delphi 2009 compiler handle recursive inline methods?

Question

Do "What's wrong with using inline functions" and "Can a recursive function be inline" apply to Delphi inline functions? Furthermore, does anyone know how recursive inline functions are handled in Delphi?

Answer 1

My guess is probably not since inline is only a suggestion, but lets find out.

A simple recursive factorial routine:

function Factorial(const aNum: cardinal): cardinal;
begin
  if aNum > 1 then
    Result := Factorial(aNum - 1) * aNum
  else
    Result := 1;
end;

Here is the disassembly of the call to it:

// fact := Factorial(5);
mov eax,$00000005
call Factorial
mov ebx,eax

And the disassembly of the routine itself:

// 9: begin
push ebx
mov ebx,eax
// 10: if aNum > 1 then
cmp ebx,$01
jbe $0040ab30
// 11: Result := Factorial(aNum - 1) * aNum
mov eax,ebx
dec eax
call Factorial
imul ebx
pop ebx
ret 
// 13: Result := 1;
0040ab30: mov eax,$00000001
// 14: end;
pop ebx
ret

Now we make it inline and see what is different in the call:

// 21: fact := Factorial(5);
mov eax,$00000005
call Factorial
mov ebx,eax

And the routine itself:

// 9: begin
push ebx
mov ebx,eax
// 10: if aNum > 1 then
cmp ebx,$01
jbe $0040ab30
// 11: Result := Factorial(aNum - 1) * aNum
mov eax,ebx
dec eax
call Factorial
imul ebx
pop ebx
ret     
// 13: Result := 1;
0040ab30: mov eax,$00000001
// 14: end;
pop ebx
ret

And they both appear the same to me, so I am going to stick with my original hypothesis and say they are not supported.

BTW: this is in Delphi 2009.