added system.default in order to prevent the abstraction inversion that 'template default(T): untyped = (var x: T; x)' causes

compiler/vmgen.nim

@@ -910,6 +910,15 @@ proc genBindSym(c: PCtx; n: PNode; dest: var TDest) =
     c.gABC(n, opcNDynBindSym, dest, x, n.len)
     c.freeTempRange(x, n.len)
 
+proc fitsRegister*(t: PType): bool =
+  assert t != nil
+  t.skipTypes(abstractInst-{tyTypeDesc}).kind in {
+    tyRange, tyEnum, tyBool, tyInt..tyUInt64, tyChar}
+
+proc ldNullOpcode(t: PType): TOpcode =
+  assert t != nil
+  if fitsRegister(t): opcLdNullReg else: opcLdNull
+
 proc genMagic(c: PCtx; n: PNode; dest: var TDest; m: TMagic) =
   case m
   of mAnd: c.genAndOr(n, opcFJmp, dest)
@@ -1129,9 +1138,13 @@ proc genMagic(c: PCtx; n: PNode; dest: var TDest; m: TMagic) =
   of mReset:
     unused(c, n, dest)
     var d = c.genx(n.sons[1])
+    # XXX use ldNullOpcode() here?
     c.gABx(n, opcLdNull, d, c.genType(n.sons[1].typ))
     c.gABx(n, opcNodeToReg, d, d)
     c.genAsgnPatch(n.sons[1], d)
+  of mDefault:
+    if dest < 0: dest = c.getTemp(n.typ)
+    c.gABx(n, ldNullOpcode(n.typ), dest, c.genType(n.typ))
   of mOf, mIs:
     if dest < 0: dest = c.getTemp(n.typ)
     var tmp = c.genx(n.sons[1])
@@ -1332,11 +1345,6 @@ const
     tyFloat, tyFloat32, tyFloat64, tyFloat128,
     tyUInt, tyUInt8, tyUInt16, tyUInt32, tyUInt64}
 
-proc fitsRegister*(t: PType): bool =
-  assert t != nil
-  t.skipTypes(abstractInst-{tyTypeDesc}).kind in {
-    tyRange, tyEnum, tyBool, tyInt..tyUInt64, tyChar}
-
 proc unneededIndirection(n: PNode): bool =
   n.typ.skipTypes(abstractInstOwned-{tyTypeDesc}).kind == tyRef
 
@@ -1766,10 +1774,6 @@ proc getNullValue(typ: PType, info: TLineInfo; conf: ConfigRef): PNode =
     globalError(conf, info, "cannot create null element for: " & $t.kind)
     result = newNodeI(nkEmpty, info)
 
-proc ldNullOpcode(t: PType): TOpcode =
-  assert t != nil
-  if fitsRegister(t): opcLdNullReg else: opcLdNull
-
 proc genVarSection(c: PCtx; n: PNode) =
   for a in n:
     if a.kind == nkCommentStmt: continue