From 638181c4f19f38898abf5ff41b891eaa62ea9325 Mon Sep 17 00:00:00 2001
From: tomsmeding <tom.smeding@gmail.com>
Date: Sat, 14 Dec 2019 22:56:31 +0100
Subject: Fix serious correctness issue in Optimiser globalPropAssigns

The optimisation pass would often not collect all assignments to a
particular reference, so that it would wrongly conclude that a reference
is only ever assigned once while it is actually assigned in multiple
places.

I have _no_ idea why this didn't result in issues before.
---
 Optimiser.hs | 1 +
 1 file changed, 1 insertion(+)

diff --git a/Optimiser.hs b/Optimiser.hs
index c59c40e..4cff2ea 100644
--- a/Optimiser.hs
+++ b/Optimiser.hs
@@ -98,6 +98,7 @@ globalPropAssigns :: [BB] -> [BB]
 globalPropAssigns bbs =
     let asgmap = map ((,) <$> fst . head <*> map snd)
                  . groupBy ((==) `on` fst)
+                 . sortOn fst
                  $ [pair | BB _ inss _ <- bbs, pair <- inss]
         replacements = concatMap (\(dest, inss) -> case inss of
                                                        [IAssign ref@(RConst _)] -> [(dest, ref)]
-- 
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