[fpc-devel] win64 calling convention

[Hans-Peter Diettrich]

Martin schrieb:
> Just to confirm my observations. (again trying to get pascal script to 
> work)
> 64 bit windows
> 
> procedure FOO(Sender: TSynEdit; const M: String; const P1, P2: TPoint);
> 
> "const P1, P2: TPoint" versus "P1, P2: TPoint"
> 
> if "const" is NOT used, then TPoint is put into a register
> if "const" is used, then TPoint is in mem, and the register is a reference.
> 
> Is that right?  (I know the doc says, no assumption, and can be ref or 
> value)

In Delphi it's clear:

Without "const" the data *must* be copied (by-val), so that the 
subroutine cannot change the original data.

"const" *allows* the compiler to pass the original data structure 
by-ref, because the subroutine will not change the data. Whether the 
parameter is passed by value or reference depends, on e.g. the sizeof 
the data structures and pointers, and whether optimizing for speed or size.

FPC has added "constref", definitely forcing by-ref. AFAIR this was 
required for the ObjectiveC interface.

DoDi