Hi,
why does fpc not remove the calculation of the return value of inline
functions, when the return value is unused?
For example
type TUtility = class
function doSomething: TUtility; inline;
end;
function TUtility.dosomething: TUtility;
begin
writeln();
result := self;
end;
adds a mov rax,rdi in the caller function, even if rax is then never
used.
{
26 begin
0x00000000004001c0 <+0>: push rbx
27 ut := TUtility.Create;
0x00000000004001c1 <+1>: movabs rsi,0x1
0x00000000004001cb <+11>: lea rdi,[rip+0x2b2fde] #
0x6b31b0 <VMT_$WTFINLINE_$$_TUTILITY>
0x00000000004001d2 <+18>: call 0x411b60
<SYSTEM$_$TOBJECT_$__$$_CREATE$$TOBJECT>
0x00000000004001d7 <+23>: mov rbx,rax
28 ut.dosomething;
0x00000000004001da <+26>: call 0x41bf20 <fpc_get_output>
0x00000000004001df <+31>: mov rdi,rax
0x00000000004001e2 <+34>: call 0x41c100 <fpc_writeln_end>
0x00000000004001e7 <+39>: call 0x416170 <fpc_iocheck>
0x00000000004001ec <+44>: mov rdi,rbx
0x00000000004001ef <+47>: mov rax,rdi
//<----------------------------------------------- here
29 ut.free;
0x00000000004001f2 <+50>: call 0x411cd0
<SYSTEM$_$TOBJECT_$__$$_FREE>
30 end;
0x00000000004001f7 <+55>: pop rbx
0x00000000004001f8 <+56>: ret
}
It is a popular pattern to add result := self; to _every_ method (or
result := @self in objects/records), so it can be chained as
dosomething().dosomething().dosomething(),.....
but one cannot use it with fpc efficiently, when it inserts too many
unnecessary instructions
Best,
Benito
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