Fix serious correctness issue in Optimiser globalPropAssignsHEADmaster

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.

1 files changed, 1 insertions, 0 deletions

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)]