[fpc-pascal] How to inline CompareFunc to Sort method in generic abstract class

[Vojtěch Čihák]

Hi,
 
I specialized my generic abstract class in a different unit with this type:
 
TRec = record
    A: Integer;
    B: Integer;
  end;
 
(A is for sorting, B is for testing of stability, i.e. for MergeSort, TimSort)
 
and compare function, declared with inline; directive:
 
function MyComptFunc(const ARec, BRec: TRec): Integer;
var i, aCnt: Integer;
begin
  aCnt:=CFComplex;
  for i:=0 to aCnt do
    Result:=(BRec.A-ARec.A);
  inc(CFCnt);
  //InterlockedIncrement(CFCnt);
end;              
 
The reason for this complex compare function is that it also measure number of comparisons and it can simulate more expensive comparisons (like sorting strings).
 
For a while, I added this unit to the second "uses" section (implementation) of the other unit, which is impractical, but I had
temporary access to the compare function. I tested again with ShellSort, sorting 2'000'000 values takes:
1380ms inlined
1515ms not inlined, ~9% slower
1430ms when compare func. is a parameter ~4% slower
 
I pass variables by value. But you are right, when I shave the function like this:
 
function MyComptFunc(const ARec, BRec: TRec): Integer;
begin
  Result:=(BRec.A-ARec.A);
end;
 
the results are:
750ms inlined
950ms not inlined, ~21% slower
835ms when compare func. is a parameter ~10% slower
 
so the gain of inlining is higher for sorting primitive types.
V.______________________________________________________________
> Od: "Flávio Etrusco via fpc-pascal" <fpc-pascal at lists.freepascal.org>
> Komu: "FPC-Pascal users discussions" <fpc-pascal at lists.freepascal.org>
> Datum: 18.11.2022 20:45
> Předmět: Re: [fpc-pascal] How to inline CompareFunc to Sort method in generic abstract class
>


Em seg., 14 de nov. de 2022 15:26, Vojtěch Čihák via fpc-pascal <fpc-pascal at lists.freepascal.org <fpc-pascal at lists.freepascal.org>> escreveu:,What do you mean by "be inlined"? The 'inline' directive instructs the compiler (or is it the linker? 😬) to try copying the whole function inline, also avoiding the call (stack) setup; you can't do this for this for a general purpose method.I'm curious how you got that 6% figure, it seems rather large. Is this comparing the parameter vs virtual method approach or comparing a fully inline (no indirect call of any kind) sort function to some other option? Are you passing the variables by reference?Best regards,Flávio
 
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