Re: =void in struct definition

[Shachar Shemesh via Digitalmars-d]

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