Missing post-blit calls when copying a static array from a slice.

[EyalIO]

This program exhibits buggy behavior:

import std.stdio:writeln;

struct Elem {
    int x = -1;
    this(int x) { this.x = x; writeln("CTOR ", x, " (", cast(void*)&this, ")"); }
    this(this) { writeln("POSTBLIT ", x, " (", cast(void*)&this, ")"); }
    ~this()    { if (x!=-1) writeln("DTOR "    , x, " (", cast(void*)&this, ")"); }
}

struct Ctr {
    Elem[3] arr;
    Elem[] slice() { return arr; }
    Elem[3] arrVal() { return arr; }
}

void main() {
    writeln("construct Ctr {");
    auto p = Ctr();
    writeln("}");
    writeln("assign arr {");
    p.arr = [Elem(1), Elem(2), Elem(3)];
    writeln("}");
    {
        writeln("slice rval -> arr {");
        Elem[3] _arr = p.slice;
        writeln("}");
    }
    {
        writeln("arr rval -> arr {");
        Elem[3] _arr = p.arrVal();
        writeln("}");
    }
}

This program fails to call POSTBLIT when copying from a slice-type, thus causing the number of CTOR/POSTBLITS to mismatch the number of DTORs.

Program's output:

construct Ctr {
}
assign arr {
CTOR 1 (7FFFCA8A2468)
CTOR 2 (7FFFCA8A2458)
CTOR 3 (7FFFCA8A2448)
}
slice rval -> arr {
}
DTOR 3 (7FFFCA8A2410)
DTOR 2 (7FFFCA8A240C)
DTOR 1 (7FFFCA8A2408)
arr rval -> arr {
POSTBLIT 1 (7FFFCA8A2370)
POSTBLIT 2 (7FFFCA8A2374)
POSTBLIT 3 (7FFFCA8A2378)
}
DTOR 3 (7FFFCA8A2400)
DTOR 2 (7FFFCA8A23FC)
DTOR 1 (7FFFCA8A23F8)
DTOR 3 (7FFFCA8A24B0)
DTOR 2 (7FFFCA8A24AC)
DTOR 1 (7FFFCA8A24A8)

Note the missing POSTBLIT printouts under slice rval -> arr {...

[EyalIO]

Similar, but different buggy behavior for the same program in dmd: https://issues.dlang.org/show_bug.cgi?id=16197

[dnadlinger]

@kinke: I guess the correct fix might be immediately obvious to you right now, after working on the other lifetime issues? The 3 elements are not necessary, by the way, just using 1 makes the output (and IR) easier to read.

[kinke]

The fault is that in visit(AssignExp*), we detect the rhs as rvalue and hence pass canSkipPostblit = true to DtoAssign() -> DtoArrayAssign(). The slice itself returned by p.slice() is an rvalue, but slices need to be treated as lvalues here.

[kinke]

Fixed by #1609.