[fpc-devel] ref count issue with out param

[Florian Klämpfl]

Am 13.06.2015 um 16:42 schrieb Martin Frb:
> On 13/06/2015 15:18, Florian Klämpfl wrote:
>> Foo2(a1[i],a2[j])
>>
>> a1, a2 being dyn. arrays, but sharing data, i and j having the same value.
>>
>>
> 
> I dug out my old "turbo delphi".
> 
> In all both cases (my original example / you dyn array example) Delphi passes nil for the normal
> parameter, and fpc passes a dangling pointer.
> 

This depends on the order in which parameters are loaded and is coincidence. Nevertheless, I'll fix
the evaluation order because the code is non-optimal (but not wrong!).

3.1.1 i386:
# [22] Foo2(s1,s1);
	movl	U_$P$PROJECT1_$$_S1,%ebx
	movl	$U_$P$PROJECT1_$$_S1,%eax
	call	fpc_ansistr_decr_ref
	movl	$U_$P$PROJECT1_$$_S1,%eax
	movl	%ebx,%edx
	call	P$PROJECT1_$$_FOO2$ANSISTRING$ANSISTRING

2.6.4 i386:
# [19] Foo1(s1,s1);
	movl	$U_P$PROJECT1_S1,%eax
	call	FPC_ANSISTR_DECR_REF
	movl	$U_P$PROJECT1_S1,%edx
	movl	U_P$PROJECT1_S1,%eax
	call	P$PROJECT1_FOO1$ANSISTRING$ANSISTRING

2.6.4 x86-64:
# [22] Foo2(s1,s1);
	movq	U_P$PROJECT1_S1(%rip),%rbx
	leaq	U_P$PROJECT1_S1(%rip),%rcx
	call	FPC_ANSISTR_DECR_REF
	leaq	U_P$PROJECT1_S1(%rip),%rcx
	movq	%rbx,%rdx
	call	P$PROJECT1_FOO2$ANSISTRING$ANSISTRING