=void in struct definition

[Shachar Shemesh]

On 09/04/18 14:22, Jonathan M Davis wrote:
> On Monday, April 09, 2018 14:06:50 Shachar Shemesh via Digitalmars-d wrote:
>> struct S {
>>     int a;
>>     int[5000] arr = void;
>> }
>>
>> void func() {
>>     S s;
>> }
>>
>> During the s initialization, the entire "S" area is initialized,
>> including the member arr which we asked to be = void.
>>
>> Is this a bug?
> 
> It looks like Andrei created an issue about it as an enhancement request
> several years ago:
> 
> https://issues.dlang.org/show_bug.cgi?id=11331
> 
> - Jonathan M Davis
> 

Except that issue talks about default constructed objects. My problem 
happens also with objects constructed with a constructor:


extern(C) void func(ref S s);

struct S {
     uint a;
     int[5000] arr = void;

     this(uint val) {
         a = val;
     }
}

void main() {
     auto s = S(12);

     // To prevent the optimizer from optimizing s away
     func(s);
}

$ ldc2 -c -O3 -g test.d
$ objdump -S -r test.o | ddemangle > test.s

0000000000000000 <_Dmain>:
     }
}

void main() {
    0:	48 81 ec 28 4e 00 00 	sub    $0x4e28,%rsp
    7:	48 8d 7c 24 04       	lea    0x4(%rsp),%rdi
     auto s = S(12);
    c:	31 f6                	xor    %esi,%esi
    e:	ba 20 4e 00 00       	mov    $0x4e20,%edx
   13:	e8 00 00 00 00       	callq  18 <_Dmain+0x18>
			14: R_X86_64_PLT32	memset-0x4
         a = val;
   18:	c7 04 24 0c 00 00 00 	movl   $0xc,(%rsp)
   1f:	48 89 e7             	mov    %rsp,%rdi

     // To prevent the optimizer from optimizing s away
     func(s);
   22:	e8 00 00 00 00       	callq  27 <_Dmain+0x27>
			23: R_X86_64_PLT32	func-0x4
}
   27:	31 c0                	xor    %eax,%eax
   29:	48 81 c4 28 4e 00 00 	add    $0x4e28,%rsp
   30:	c3                   	retq


Notice the call to memset.

Shachar