fix #15609 (#15856)

* fix #15609

* fix test

compiler/injectdestructors.nim

@@ -824,10 +824,6 @@ proc p(n: PNode; c: var Con; s: var Scope; mode: ProcessMode): PNode =
     of nkAsgn, nkFastAsgn:
       if hasDestructor(c, n[0].typ) and n[1].kind notin {nkProcDef, nkDo, nkLambda} and
           not isCursor(n[0], c):
-        # rule (self-assignment-removal):
-        if n[1].kind == nkSym and n[0].kind == nkSym and n[0].sym == n[1].sym:
-          result = newNodeI(nkEmpty, n.info)
-        else:
         if n[0].kind in {nkDotExpr, nkCheckedFieldExpr}:
           cycleCheck(n, c)
         assert n[1].kind notin {nkAsgn, nkFastAsgn}
@@ -955,7 +951,10 @@ proc moveOrCopy(dest, ri: PNode; c: var Con; s: var Scope, isDecl = false): PNod
   of nkObjConstr, nkTupleConstr, nkClosure, nkCharLit..nkNilLit:
     result = c.genSink(dest, p(ri, c, s, consumed), isDecl)
   of nkSym:            
-    if isSinkParam(ri.sym) and isLastRead(ri, c):
+    if dest.kind == nkSym and dest.sym == ri.sym:
+      # rule (self-assignment-removal):
+      result = newNodeI(nkEmpty, dest.info)
+    elif isSinkParam(ri.sym) and isLastRead(ri, c):
       # Rule 3: `=sink`(x, z); wasMoved(z)
       let snk = c.genSink(dest, ri, isDecl)
       result = newTree(nkStmtList, snk, c.genWasMoved(ri))

tests/arc/tmovebug.nim

@@ -70,6 +70,9 @@ king
 hi
 try
 bye
+()
+()
+()
 '''
 """
 
@@ -524,3 +527,33 @@ proc getScope2(): string =
     "else"
 
 echo getScope2()
+
+
+#--------------------------------------------------------------------
+#bug  #15609
+
+type
+  Wrapper = object
+    discard
+
+proc newWrapper(): ref Wrapper =
+  new(result)
+  result
+
+
+proc newWrapper2(a: int): ref Wrapper =
+  new(result)
+  if a > 0:
+    result
+  else:
+    new(Wrapper)
+
+
+let w1 = newWrapper()
+echo $w1[]
+
+let w2 = newWrapper2(1)
+echo $w2[]
+
+let w3 = newWrapper2(-1)
+echo $w3[]