fixes move analyser; refs #11257

compiler/injectdestructors.nim

@@ -178,13 +178,13 @@ proc isLastRead(location: PNode; c: var Con; pc, comesFrom: int): int =
       pc = pc + c.g[pc].dest
     of fork:
       # every branch must lead to the last read of the location:
-      var variantA = isLastRead(location, c, pc+1, pc)
+      let variantA = isLastRead(location, c, pc+1, pc)
       if variantA < 0: return -1
-      let variantB = isLastRead(location, c, pc + c.g[pc].dest, pc)
+      var variantB = isLastRead(location, c, pc + c.g[pc].dest, pc)
       if variantB < 0: return -1
-      elif variantA == high(int):
-        variantA = variantB
-      pc = variantA
+      elif variantB == high(int):
+        variantB = variantA
+      pc = variantB
     of InstrKind.join:
       let dest = pc + c.g[pc].dest
       if dest == comesFrom: return pc + 1

tests/destructor/tconsume_twice.nim

@@ -0,0 +1,12 @@
+discard """
+  cmd: "nim c --newruntime $file"
+  errormsg: "sink parameter `a` is already consumed at tconsume_twice.nim(8, 6)"
+  line: 10
+"""
+
+proc consumeTwice(a: owned proc()): owned proc() =
+  if a == nil:
+    return
+  return a
+
+assert consumeTwice(proc() = discard) != nil