[fpc-pascal] SetLength warnings - request

[Benito van der Zander]

Hi,

> even if there's closed issue 
> https://bugs.freepascal.org/view.php?id=34169 I would like to ask if 
> it can be reconsidered.
>
> The subject is that SetLength now gives warning: Variable "dynamic 
> array" of a managed type does not seem to be initialized
>
> in 3.3.1 and 3.1.1 while it doesn't give any warning in stable 3.0.4
>

seriously that is such a bullshit warning.

SetLength is called to initialize the variable, of course the variable 
is not initialized before. If it was initialized, we might not even need 
to call SetLength

Cheers,
Benito

Am 04.09.18 um 15:53 schrieb Vojtěch Čihák:
>
> Hello,
>
> even if there's closed issue 
> https://bugs.freepascal.org/view.php?id=34169 I would like to ask if 
> it can be reconsidered.
>
> The subject is that SetLength now gives warning: Variable "dynamic 
> array" of a managed type does not seem to be initialized
>
> in 3.3.1 and 3.1.1 while it doesn't give any warning in stable 3.0.4
>
> As a solution is recommended do declaration: var arr: array of 
> widechar = ();
>
> But it means that initialization is in fact done twice. See assembler 
> of following code:
>
> procedure TForm1.Button1Click(Sender: TObject);
>
> var DA: array of widechar = ();
>
> begin
>
>   SetLength(DA, 10);
>
>   writeln(DA[0]);
>
> end;
>
> unit1.pas:30                     var DA: array of widechar = ();
>
> 00000000004696C9 488d1538536600           lea    0x665338(%rip),%rdx  
>       # 0xacea08 <RTTI_$UNIT1_$$_def00000138>
>
> 00000000004696D0 488b3529536600           mov    0x665329(%rip),%rsi  
>       # 0xacea00 <TC_$UNIT1$_$TFORM1_$_BUTTON1CLICK$TOBJECT_$$_defaultDA>
>
> 00000000004696D7 4889e7                   mov    %rsp,%rdi
>
> 00000000004696DA e8d199fcff               callq  0x4330b0 
> <fpc_dynarray_assign>
>
> unit1.pas:32                     SetLength(DA, 10);
>
> 00000000004696DF 48c74424680a000000       movq   $0xa,0x68(%rsp)
>
> 00000000004696E8 488d3519536600           lea    0x665319(%rip),%rsi  
>       # 0xacea08 <RTTI_$UNIT1_$$_def00000138>
>
> 00000000004696EF 488d4c2468               lea    0x68(%rsp),%rcx
>
> 00000000004696F4 4889e7                   mov    %rsp,%rdi
>
> 00000000004696F7 ba01000000               mov    $0x1,%edx
>
> 00000000004696FC e8df99fcff               callq  0x4330e0 
> <fpc_dynarray_setlength>
>
> unit1.pas:33                     writeln(DA[0]);
>
> To avoid warning we now need four extra instructions incl. call to 
> fpc_array_assign, which is obviously redundant.
> As an explanation is written: Setlength uses a var parameter. This is 
> no different from other cases of var parameter usage.
> I disaggre here, because SetLength is not an usual procedure, it is 
> fundamental part of compiler. Therefore it deserves some exception.
> That's why I ask for reconsidering and make it behave like in 3.0.4 or 
> change declaration from "var" to "out" as it is done in getmem().
> Thanks, Vojtěch.
>
> _______________________________________________
> fpc-pascal maillist  -  fpc-pascal at lists.freepascal.org
> http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
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