object copy broken in vm

[timotheecour]

I found this issue while investigating ways to fix swap double evaluation bug in vm #16779; this runs into the following issue, that object copy seems broken in vm

Example

when true:
  template swap*[T](a, b: var T) =
    var a2 = addr(a)
    var b2 = addr(b)
    var aOld = a2[]
    a2[] = b2[]
    b2[] = aOld

  proc main =
    block:
      var a = 1
      var b = 2
      swap(a, b)
      echo (a,b)

    block:
      type Foo = ref object
        x: int
      var a = Foo(x:1)
      var b = Foo(x:2)
      swap(a, b)
      echo (a.x, b.x)

    block:
      type Foo = object
        x: int
      var a = Foo(x:1)
      var b = Foo(x:2)
      swap(a, b)
      echo (a.x,b.x)

  static: main()
  main()

Current Output

nim r main:
vm:
(2, 1)
(2, 1)
(1, 2)
rt:
(2, 1)
(2, 1)
(2, 1)

nim r -b:js main:
ditto

Expected Output

nim r main:
vm:
(2, 1)
(2, 1)
(2, 1)
rt:
(2, 1)
(2, 1)
(2, 1)

nim r -b:js main:
ditto

Additional Information

• 1.5.1 2b5841c
• note that this issue isn't a stdlib issue nor an issue with swap, it's an issue with VM