From b613092de8b4b4625c8a2e8b29d64c5a8e49287e Mon Sep 17 00:00:00 2001
From: LemonBoy <LemonBoy@users.noreply.github.com>
Date: Mon, 22 Oct 2018 17:09:15 +0200
Subject: [PATCH] Don't crash if GC_{un,}ref is called on nil (#9445)

Fixes #9442
---
 compiler/ccgexprs.nim    |  4 ++--
 tests/magics/tmagics.nim | 11 +++++++++++
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/compiler/ccgexprs.nim b/compiler/ccgexprs.nim
index d73dac82fc..44967961eb 100644
--- a/compiler/ccgexprs.nim
+++ b/compiler/ccgexprs.nim
@@ -2008,8 +2008,8 @@ 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,
diff --git a/tests/magics/tmagics.nim b/tests/magics/tmagics.nim
index d13a036bdf..841de56a58 100644
--- a/tests/magics/tmagics.nim
+++ b/tests/magics/tmagics.nim
@@ -43,3 +43,14 @@ block t8693:
   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)