fixes #6955

tests/effects/tgcsafe.nim

@@ -1,9 +1,18 @@
 discard """
   errormsg: "'mainUnsafe' is not GC-safe"
-  line: 17
+  line: 26
   cmd: "nim $target --hints:on --threads:on $options $file"
 """
 
+# bug #6955
+var global_proc: proc(a: string): int {.nimcall.} = nil
+
+proc myproc(i: int) {.gcsafe.} =
+  if global_proc != nil:
+    echo "a"
+  if isNil(global_proc):
+    return
+
 proc mymap(x: proc ()) =
   x()