Remove uniqSetToList

This documents nondeterminism in code generation and removes
the nondeterministic ufmToList function. In the future someone
will have to use nonDetEltsUFM (with proper explanation)
or pprUFM.

4 files changed, 21 insertions, 15 deletions

diff --git a/compiler/utils/GraphColor.hs b/compiler/utils/GraphColor.hs
index 41b367692a..8a1cdd0952 100644
--- a/compiler/utils/GraphColor.hs
+++ b/compiler/utils/GraphColor.hs
@@ -309,8 +309,9 @@ selectColor colors graph u
         Just nsConflicts
                         = sequence
                         $ map (lookupNode graph)
-                        $ uniqSetToList
+                        $ nonDetEltsUFM
                         $ nodeConflicts node
+                        -- See Note [Unique Determinism and code generation]
 
         colors_conflict = mkUniqSet
                         $ catMaybes
@@ -355,7 +356,8 @@ selectColor colors graph u
 
                 -- it wasn't a preference, but it was still ok
                 | not $ isEmptyUniqSet colors_ok
-                , c : _         <- uniqSetToList colors_ok
+                , c : _         <- nonDetEltsUFM colors_ok
+                -- See Note [Unique Determinism and code generation]
                 = Just c
 
                 -- no colors were available for us this time.
diff --git a/compiler/utils/GraphOps.hs b/compiler/utils/GraphOps.hs
index 8b194adba5..a4c565f2eb 100644
--- a/compiler/utils/GraphOps.hs
+++ b/compiler/utils/GraphOps.hs
@@ -89,11 +89,12 @@ delNode k graph
         | Just node     <- lookupNode graph k
         = let   -- delete conflict edges from other nodes to this one.
                 graph1  = foldl' (\g k1 -> let Just g' = delConflict k1 k g in g') graph
-                        $ uniqSetToList (nodeConflicts node)
+                        $ nonDetEltsUFM (nodeConflicts node)
 
                 -- delete coalesce edge from other nodes to this one.
                 graph2  = foldl' (\g k1 -> let Just g' = delCoalesce k1 k g in g') graph1
-                        $ uniqSetToList (nodeCoalesce node)
+                        $ nonDetEltsUFM (nodeCoalesce node)
+                        -- See Note [Unique Determinism and code generation]
 
                 -- delete the node
                 graph3  = graphMapModify (\fm -> delFromUFM fm k) graph2
@@ -181,7 +182,7 @@ addConflicts
 addConflicts conflicts getClass
 
         -- just a single node, but no conflicts, create the node anyway.
-        | (u : [])      <- uniqSetToList conflicts
+        | (u : [])      <- nonDetEltsUFM conflicts
         = graphMapModify
         $ adjustWithDefaultUFM
                 id
@@ -191,7 +192,8 @@ addConflicts conflicts getClass
         | otherwise
         = graphMapModify
         $ (\fm -> foldl' (\g u  -> addConflictSet1 u getClass conflicts g) fm
-                $ uniqSetToList conflicts)
+                $ nonDetEltsUFM conflicts)
+                -- See Note [Unique Determinism and code generation]
 
 
 addConflictSet1 :: Uniquable k
@@ -315,7 +317,8 @@ coalesceGraph' aggressive triv graph kkPairsAcc
         --
         cList   = [ (nodeId node1, k2)
                         | node1 <- cNodes
-                        , k2    <- uniqSetToList $ nodeCoalesce node1 ]
+                        , k2    <- nonDetEltsUFM $ nodeCoalesce node1 ]
+                        -- See Note [Unique Determinism and code generation]
 
         -- do the coalescing, returning the new graph and a list of pairs of keys
         --      that got coalesced together.
@@ -562,7 +565,7 @@ validateGraph doc isColored graph
         , not $ isEmptyUniqSet badEdges
         = pprPanic "GraphOps.validateGraph"
                 (  text "Graph has edges that point to non-existant nodes"
-                $$ text "  bad edges: " <> vcat (map ppr $ uniqSetToList badEdges)
+                $$ text "  bad edges: " <> pprUFM badEdges (vcat . map ppr)
                 $$ doc )
 
         -- Check that no conflicting nodes have the same color
@@ -602,7 +605,8 @@ checkNode
 checkNode graph node
         | Just color            <- nodeColor node
         , Just neighbors        <- sequence $ map (lookupNode graph)
-                                $  uniqSetToList $ nodeConflicts node
+                                $  nonDetEltsUFM $ nodeConflicts node
+            -- See Note [Unique Determinism and code generation]
 
         , neighbourColors       <- catMaybes $ map nodeColor neighbors
         , elem color neighbourColors
diff --git a/compiler/utils/GraphPpr.hs b/compiler/utils/GraphPpr.hs
index 6f7e9d5bb2..9c246893f7 100644
--- a/compiler/utils/GraphPpr.hs
+++ b/compiler/utils/GraphPpr.hs
@@ -86,7 +86,8 @@ dotNode colorMap triv node
         excludes
                 = hcat $ punctuate space
                 $ map (\n -> text "-" <> ppr n)
-                $ uniqSetToList $ nodeExclusions node
+                $ nonDetEltsUFM $ nodeExclusions node
+                -- See Note [Unique Determinism and code generation]
 
         preferences
                 = hcat $ punctuate space
@@ -144,12 +145,14 @@ dotNodeEdges visited node
         | otherwise
         = let   dconflicts
                         = map (dotEdgeConflict (nodeId node))
-                        $ uniqSetToList
+                        $ nonDetEltsUFM
+                        -- See Note [Unique Determinism and code generation]
                         $ minusUniqSet (nodeConflicts node) visited
 
                 dcoalesces
                         = map (dotEdgeCoalesce (nodeId node))
-                        $ uniqSetToList
+                        $ nonDetEltsUFM
+                        -- See Note [Unique Determinism and code generation]
                         $ minusUniqSet (nodeCoalesce node) visited
 
                 out     =  vcat dconflicts
diff --git a/compiler/utils/UniqSet.hs b/compiler/utils/UniqSet.hs
index 925997f45a..f08fa866c1 100644
--- a/compiler/utils/UniqSet.hs
+++ b/compiler/utils/UniqSet.hs
@@ -29,7 +29,6 @@ module UniqSet (
         sizeUniqSet,
         isEmptyUniqSet,
         lookupUniqSet,
-        uniqSetToList,
         partitionUniqSet
     ) where
 
@@ -69,7 +68,6 @@ partitionUniqSet :: (a -> Bool) -> UniqSet a -> (UniqSet a, UniqSet a)
 sizeUniqSet :: UniqSet a -> Int
 isEmptyUniqSet :: UniqSet a -> Bool
 lookupUniqSet :: Uniquable a => UniqSet b -> a -> Maybe b
-uniqSetToList :: UniqSet a -> [a]
 
 {-
 ************************************************************************
@@ -116,7 +114,6 @@ partitionUniqSet = partitionUFM
 sizeUniqSet = sizeUFM
 isEmptyUniqSet = isNullUFM
 lookupUniqSet = lookupUFM
-uniqSetToList = eltsUFM
 
 uniqSetAny :: (a -> Bool) -> UniqSet a -> Bool
 uniqSetAny = anyUFM