From 7775b7efd1f3a7eca434710d90368b98198019bd Mon Sep 17 00:00:00 2001
From: LemonBoy <LemonBoy@users.noreply.github.com>
Date: Thu, 11 Oct 2018 08:36:05 +0200
Subject: [PATCH] Fix wrong heuristic in codegen (#9293)

A bare return may trigger the insertion of a genericReset.

Fixes #9286
---
 compiler/cgen.nim       |  8 +++++++-
 tests/ccgbugs/t9286.nim | 22 ++++++++++++++++++++++
 2 files changed, 29 insertions(+), 1 deletion(-)
 create mode 100644 tests/ccgbugs/t9286.nim

diff --git a/compiler/cgen.nim b/compiler/cgen.nim
index 918bec0f92..37b07d38dc 100644
--- a/compiler/cgen.nim
+++ b/compiler/cgen.nim
@@ -771,7 +771,13 @@ proc allPathsAsgnResult(n: PNode): InitResultEnum =
       result = InitRequired
   of nkReturnStmt:
     if n.len > 0:
-      result = allPathsAsgnResult(n[0])
+      if n[0].kind == nkEmpty and result != InitSkippable:
+        # This is a bare `return` statement, if `result` was not initialized
+        # anywhere else (or if we're not sure about this) let's require it to be
+        # initialized. This avoids cases like #9286 where this heuristic lead to
+        # wrong code being generated.
+        result = InitRequired
+      else: result = allPathsAsgnResult(n[0])
   of nkIfStmt, nkIfExpr:
     var exhaustive = false
     result = InitSkippable
diff --git a/tests/ccgbugs/t9286.nim b/tests/ccgbugs/t9286.nim
new file mode 100644
index 0000000000..8a45a7bf60
--- /dev/null
+++ b/tests/ccgbugs/t9286.nim
@@ -0,0 +1,22 @@
+discard """
+  action: run
+"""
+
+import options
+type Foo  = ref object
+  i:      int
+
+proc next(foo: Foo): Option[Foo] =
+  try:    assert(foo.i == 0)
+  except: return      # 2º: none
+  return some(foo)    # 1º: some
+
+proc test =
+  let foo = Foo()
+  var opt = next(foo) # 1º Some
+  while isSome(opt) and foo.i < 10:
+    inc(foo.i)
+    opt = next(foo)   # 2º None
+  assert foo.i == 1, $foo.i
+
+test()