On 14/07/2019 04:08, J. Gareth Moreton wrote:
> Just a thought that I'd chuck in on this... I did wonder how practical
> it would be to store checksums of all compiled procedures and the like
> and to look for collisions. When studying how the compiler is built, I
> noticed a lot of the internal methods, due to conditional defines, would
> compile into identical code, so merging them would reduce the binary
> size if the linker is able to strip out procedures that are never
> called. Granted, I haven't done research on how Free Pascal does Whole
> Program Optimisation yet, especially as it requiring a separate
> compilation pass has always put me off. I would have thought that the
> linker should be able to handle it right there and then because it has
> all the information it needs.
Optimising linkers that do this exist. However, it's tricky to do it in
a safe way because programs may compare addresses of functions to
determine what to do. If those addresses become equal, program behaviour
can change. E.g.
procedure test1;
begin
end;
procedure test2;
begin
end;
procedure doit(proc: tprocedure);
begin
if proc=@test1 then
writeln('test1')
else
writeln('test2');
end;
begin
doit(@test1);
doit(@test2);
end.
Jonas
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