Support system.reset in vm (#10400)

(cherry picked from commit a4cdd25b19)

compiler/vm.nim

@@ -1201,8 +1201,6 @@ proc rawExecute(c: PCtx, start: int, tos: PStackFrame): TFullReg =
       let newLen = regs[rb].intVal.int
       if regs[ra].node.isNil: stackTrace(c, tos, pc, errNilAccess)
       else: c.setLenSeq(regs[ra].node, newLen, c.debug[pc])
-    of opcReset:
-      internalError(c.config, c.debug[pc], "too implement")
     of opcNarrowS:
       decodeB(rkInt)
       let min = -(1.BiggestInt shl (rb-1))

compiler/vmdef.nim

@@ -69,7 +69,7 @@ type
     opcContainsSet, opcRepr, opcSetLenStr, opcSetLenSeq,
     opcIsNil, opcOf, opcIs,
     opcSubStr, opcParseFloat, opcConv, opcCast,
-    opcQuit, opcReset,
+    opcQuit,
     opcNarrowS, opcNarrowU,
 
     opcAddStrCh,

compiler/vmgen.nim

@@ -1063,7 +1063,9 @@ proc genMagic(c: PCtx; n: PNode; dest: var TDest; m: TMagic) =
   of mReset:
     unused(c, n, dest)
     var d = c.genx(n.sons[1])
-    c.gABC(n, opcReset, d)
+    c.gABx(n, opcLdNull, d, c.genType(n.sons[1].typ))
+    c.gABx(n, opcNodeToReg, d, d)
+    c.genAsgnPatch(n.sons[1], d)
   of mOf, mIs:
     if dest < 0: dest = c.getTemp(n.typ)
     var tmp = c.genx(n.sons[1])

tests/vm/treset.nim

@@ -0,0 +1,28 @@
+static:
+  type Obj = object
+    field: int
+  var o = Obj(field: 1)
+  reset(o)
+  doAssert o.field == 0
+
+static:
+  var i = 2
+  reset(i)
+  doAssert i == 0
+
+static:
+  var i = new int
+  reset(i)
+  doAssert i.isNil
+
+static:
+  var s = @[1, 2, 3]
+  reset(s)
+  doAssert s == @[]
+
+static:
+  proc f() =
+    var i = 2
+    reset(i)
+    doAssert i == 0
+  f()