From bf1a583fdaad45e79625690dcd43244331105558 Mon Sep 17 00:00:00 2001
From: whitequark <whitequark@whitequark.org>
Date: Fri, 27 Nov 2015 18:02:18 +0800
Subject: [PATCH] compiler.types: fix TVar.find() for very large paths.

---
 artiq/compiler/types.py | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/artiq/compiler/types.py b/artiq/compiler/types.py
index 16f21c913..795e8f80e 100644
--- a/artiq/compiler/types.py
+++ b/artiq/compiler/types.py
@@ -60,8 +60,18 @@ class TVar(Type):
         if self.parent is self:
             return self
         else:
-            root = self.parent.find()
-            self.parent = root # path compression
+            # The recursive find() invocation is turned into a loop
+            # because paths resulting from unification of large arrays
+            # can easily cause a stack overflow.
+            root = self
+            while isinstance(root, TVar):
+                if root is root.parent:
+                    break
+                else:
+                    root = root.parent
+
+            # path compression
+            self.parent = root
             return root
 
     def unify(self, other):