Move semantics not respected

[dlangBugzillaToGithub]

badlink reported this on 2013-09-20T05:08:41Z

Transferred from https://issues.dlang.org/show_bug.cgi?id=11073

CC List

Description

DMD version: 2.063.2

Code: http://pastebin.com/sTLhnNdV

Output:
CTor A with 42
CTor A with 23
CTor A with 65
Value call with A::65
DTor A with 65
CTor A with 1337
Value call with A::1337
DTor A with 1337
Ref call with A::42
DTor A with 23
DTor A with 42

Disassembly: http://pastebin.com/5emmwqJc
Compilation flags: -release -O

Issue:
The first two value calls receive their arguments via move semantics, i.e. the argument is not copied but passed directly to the function.
This behavior is showed in the output (the postblit function is not called) but the disassembly shows that the struct is actually copied before the function call.

[dlangBugzillaToGithub]

rswhite4 commented on 2013-09-20T11:42:14Z

If that is fixed, there could be a huge performance boost.

[WalterBright]

The sample code:

import std.stdio;
 
struct A {
public:
    uint id;
    uint data[128];
    
    this(uint id) {
        this.id = id;
        
        writeln("CTor A with ", id);
    }
    
    this(this) {
        writeln("Postblit A with ", this.id);
    }
    
    ~this() {
        writeln("DTor A with ", this.id);
    }
    
    A opBinary(string op : "+")(ref const A a) {
        A r = A(this.id + a.id);
        r.data[] += a.data[];
        return r;
    }
}
 
void func(const A a) {
    writeln("Value call with A::", a.id);   
}
 
void func(ref const A a) {
    writeln("Ref call with A::", a.id);
}
 
void main()
{
    A a = A(42);
    A b = A(23);
    
    asm { int 3; }
    func(a + b);
    asm { int 3; }
    func(A(1337));
    func(a);
}

[TurkeyMan]

I'm pretty confident this will be resolved by __rvalue semantics. The unit tests in Walter's branch already prove these things as far as I can tell.

[thewilsonator]

closing this then