[Issue 24822] New: When passing a non-POD argument to an rvalue parameter, an unnecessary blit is done

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=24822

          Issue ID: 24822
           Summary: When passing a non-POD argument to an rvalue
                    parameter, an unnecessary blit is done
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: bugzilla at digitalmars.com

Consider:

  struct S {
    int i;
    this(ref S);
    void opAssign(S s) { i = s.i + 1; }
  }

  void test() {
    S s;
    S t;
    t = s; // call to opAssign
  }

The generated code for test() is:

0000:   55                       push      RBP
0001:   48 8B EC                 mov       RBP,RSP
0004:   48 83 EC 10              sub       RSP,010h
0008:   31 C0                    xor       EAX,EAX
000a:   89 45 F0                 mov       -010h[RBP],EAX
000d:   89 45 F4                 mov       -0Ch[RBP],EAX
0010:   89 45 F8                 mov       -8[RBP],EAX
0013:   48 8D 75 F0              lea       RSI,-010h[RBP]
0017:   48 8D 7D F8              lea       RDI,-8[RBP]
001b:   E8 00 00 00 00           call      __ctor
0020:   48 8D 75 F8              lea       RSI,-8[RBP]
0024:   48 8D 7D FC              lea       RDI,-4[RBP]
0028:   A5                       movsd     // blit copy, should not be here
0029:   48 8D 75 FC              lea       RSI,-4[RBP]
002d:   48 8D 7D F4              lea       RDI,-0Ch[RBP]
0031:   E8 00 00 00 00           call      L0
0036:   C9                       leave
0037:   C3                       ret

The blit copy is redundant and should not be generated.

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