Related: 9666

Given:

  import core.stdc.stdio;

  struct S {
    this(ref S) { printf("this(ref S)\n"); }
    void opAssign(ref S) { printf("opAssign(ref S)\n"); }
    void opAssign(S) { printf("opAssign(S)\n"); }
    void opMove(ref S) { printf("opMove(ref S)\n"); }
  }

  void main() {
    S s;
    S t;

    S test() { S* p = &s; return *p; }
    t = test();
  }

The code generated for main() is:

_Dmain:
    push      RBP
    mov       RBP,RSP
    sub       RSP,010h
    xor       EAX,EAX
    mov       -8[RBP],AL  // S s;
    mov       -7[RBP],AL  // S t;
    lea       RSI,-6[RBP] // address of struct return value
    mov       RDI,RBP     // static link
    call      test
    mov       RSI,RAX     // address of struct return value as source
    lea       RDI,-5[RBP] // address of temporary
    movsb                 // copy return value to temporary
    lea       RSI,-5[RBP] // address of temporary
    lea       RDI,-7[RBP] // address of t
    call      opAssign    // opAssign(S)
    xor       EAX,EAX
    leave
    ret

The copy is not necessary, and is a bug.