C codegen: support system.move and system.wasMoved

compiler/ccgexprs.nim

@@ -1864,6 +1864,23 @@ proc binaryFloatArith(p: BProc, e: PNode, d: var TLoc, m: TMagic) =
   else:
     binaryArith(p, e, d, m)
 
+proc skipAddr(n: PNode): PNode =
+  result = if n.kind in {nkAddr, nkHiddenAddr}: n[0] else: n
+
+proc genWasMoved(p: BProc; n: PNode) =
+  var a: TLoc
+  initLocExpr(p, n[1].skipAddr, a)
+  resetLoc(p, a)
+  #linefmt(p, cpsStmts, "#nimZeroMem((void*)$1, sizeof($2));$n",
+  #  addrLoc(p.config, a), getTypeDesc(p.module, a.t))
+
+proc genMove(p: BProc; n: PNode; d: var TLoc) =
+  if d.k == locNone: getTemp(p, n.typ, d)
+  var a: TLoc
+  initLocExpr(p, n[1].skipAddr, a)
+  genAssignment(p, d, a, {})
+  resetLoc(p, a)
+
 proc genMagicExpr(p: BProc, e: PNode, d: var TLoc, op: TMagic) =
   case op
   of mOr, mAnd: genAndOr(p, e, d, op)
@@ -1991,6 +2008,8 @@ proc genMagicExpr(p: BProc, e: PNode, d: var TLoc, op: TMagic) =
     initLocExpr(p, e.sons[2], b)
     genDeepCopy(p, a, b)
   of mDotDot, mEqCString: genCall(p, e, d)
+  of mWasMoved: genWasMoved(p, e)
+  of mMove: genMove(p, e, d)
   else:
     when defined(debugMagics):
       echo p.prc.name.s, " ", p.prc.id, " ", p.prc.flags, " ", p.prc.ast[genericParamsPos].kind

tests/destructor/texplicit_move.nim

@@ -0,0 +1,19 @@
+
+discard """
+  output: '''3
+0
+destroyed!'''
+"""
+
+type
+  myseq* = object
+    f: int
+
+proc `=destroy`*(x: var myseq) =
+  echo "destroyed!"
+
+var
+  x: myseq
+x.f = 3
+echo move(x.f)
+echo x.f