cherry pick

compiler/ccgexprs.nim

@@ -1976,8 +1976,8 @@ proc genMagicExpr(p: BProc, e: PNode, d: var TLoc, op: TMagic) =
       frmt = "$1 = $2->len;$n"
     lineCg(p, cpsStmts, frmt, tmp.r, rdLoc(a))
     putIntoDest(p, d, e, tmp.r)
-  of mGCref: unaryStmt(p, e, d, "#nimGCref($1);$n")
-  of mGCunref: unaryStmt(p, e, d, "#nimGCunref($1);$n")
+  of mGCref: unaryStmt(p, e, d, "if ($1) { #nimGCref($1); }$n")
+  of mGCunref: unaryStmt(p, e, d, "if ($1) { #nimGCunref($1); }$n")
   of mSetLengthStr: genSetLengthStr(p, e, d)
   of mSetLengthSeq: genSetLengthSeq(p, e, d)
   of mIncl, mExcl, mCard, mLtSet, mLeSet, mEqSet, mMulSet, mPlusSet, mMinusSet,

tests/magics/tmagics.nim

@@ -0,0 +1,56 @@
+discard """
+  output: '''
+true
+true
+false
+true
+true
+false
+true
+'''
+"""
+
+block tlowhigh:
+  type myEnum = enum e1, e2, e3, e4, e5
+  var a: array[myEnum, int]
+  
+  for i in low(a) .. high(a):
+    a[i] = 0
+  
+  proc sum(a: openarray[int]): int =
+    result = 0
+    for i in low(a)..high(a):
+      inc(result, a[i])
+  
+  doAssert sum([1, 2, 3, 4]) == 10
+
+
+block t8693:
+  type Foo = int | float
+
+  proc bar(t1, t2: typedesc): bool =
+    echo (t1 is t2)
+    (t2 is t1)
+
+  proc bar[T](x: T, t2: typedesc): bool =
+    echo (T is t2)
+    (t2 is T)
+
+  doAssert bar(int, Foo) == false
+  doAssert bar(4, Foo) == false
+  doAssert bar(any, int)
+  doAssert bar(int, any) == false
+  doAssert bar(Foo, Foo)
+  doAssert bar(any, Foo)
+  doAssert bar(Foo, any) == false
+
+block t9442:
+  var v1: ref char
+  var v2: string
+  var v3: seq[char]
+  GC_ref(v1)
+  GC_unref(v1)
+  GC_ref(v2)
+  GC_unref(v2)
+  GC_ref(v3)
+  GC_unref(v3)