Document some codegen nondeterminism

Bit-for-bit reproducible binaries are not a goal for now,
so this is just marking places that could be a problem.
Doing this will allow eltsUFM to be removed and will
leave only nonDetEltsUFM.

GHC Trac: #4012

compiler/cmm/CmmCommonBlockElim.hs

@@ -297,5 +297,6 @@ groupByLabel = go (TM.emptyTM :: TM.ListMap UniqDFM a)
 
 
 groupByInt :: (a -> Int) -> [a] -> [[a]]
-groupByInt f xs = eltsUFM $ List.foldl' go emptyUFM xs
+groupByInt f xs = nonDetEltsUFM $ List.foldl' go emptyUFM xs
+  -- See Note [Unique Determinism and code generation]
   where go m x = alterUFM (Just . maybe [x] (x:)) m (f x)

compiler/cmm/CmmLayoutStack.hs

@@ -184,7 +184,7 @@ instance Outputable StackMap where
      text "Sp = " <> int sm_sp $$
      text "sm_args = " <> int sm_args $$
      text "sm_ret_off = " <> int sm_ret_off $$
-     text "sm_regs = " <> ppr (eltsUFM sm_regs)
+     text "sm_regs = " <> pprUFM sm_regs ppr
 
 
 cmmLayoutStack :: DynFlags -> ProcPointSet -> ByteOff -> CmmGraph
@@ -684,7 +684,8 @@ allocate dflags ret_off live stackmap@StackMap{ sm_sp = sp0
                    | x <- [ 1 .. toWords dflags ret_off] ]
                   live_words =
                    [ (toWords dflags x, Occupied)
-                   | (r,off) <- eltsUFM regs1,
+                   | (r,off) <- nonDetEltsUFM regs1,
+                   -- See Note [Unique Determinism and code generation]
                      let w = localRegBytes dflags r,
                      x <- [ off, off - wORD_SIZE dflags .. off - w + 1] ]
    in
@@ -964,7 +965,9 @@ stackMapToLiveness dflags StackMap{..} =
                                      toWords dflags (sm_sp - sm_args)) live_words
    where
      live_words =  [ (toWords dflags off, False)
-                   | (r,off) <- eltsUFM sm_regs, isGcPtrType (localRegType r) ]
+                   | (r,off) <- nonDetEltsUFM sm_regs
+                   , isGcPtrType (localRegType r) ]
+                   -- See Note [Unique Determinism and code generation]
 
 
 -- -----------------------------------------------------------------------------
@@ -1118,4 +1121,5 @@ insertReloads stackmap =
 
 
 stackSlotRegs :: StackMap -> [(LocalReg, StackLoc)]
-stackSlotRegs sm = eltsUFM (sm_regs sm)
+stackSlotRegs sm = nonDetEltsUFM (sm_regs sm)
+  -- See Note [Unique Determinism and code generation]

compiler/nativeGen/AsmCodeGen.hs

@@ -432,7 +432,9 @@ cmmNativeGens dflags this_mod modLoc ncgImpl h dbgMap us
         -- Generate .file directives for every new file that has been
         -- used. Note that it is important that we generate these in
         -- ascending order, as Clang's 3.6 assembler complains.
-        let newFileIds = sortBy (comparing snd) $ eltsUFM $ fileIds' `minusUFM` fileIds
+        let newFileIds = sortBy (comparing snd) $
+                         nonDetEltsUFM $ fileIds' `minusUFM` fileIds
+            -- See Note [Unique Determinism and code generation]
             pprDecl (f,n) = text "\t.file " <> ppr n <+>
                             doubleQuotes (ftext f)
 

compiler/nativeGen/RegAlloc/Graph/Main.hs

@@ -401,7 +401,8 @@ patchRegsFromGraph platform graph code
 --  We need to deepSeq the whole graph before trying to colour it to avoid
 --  space leaks.
 seqGraph :: Color.Graph VirtualReg RegClass RealReg -> ()
-seqGraph graph          = seqNodes (eltsUFM (Color.graphMap graph))
+seqGraph graph          = seqNodes (nonDetEltsUFM (Color.graphMap graph))
+   -- See Note [Unique Determinism and code generation]
 
 seqNodes :: [Color.Node VirtualReg RegClass RealReg] -> ()
 seqNodes ns

compiler/nativeGen/RegAlloc/Graph/Spill.hs

@@ -376,6 +376,5 @@ makeSpillStats s
 
 instance Outputable SpillStats where
  ppr stats
-        = (vcat $ map (\(r, s, l) -> ppr r <+> int s <+> int l)
-                        $ eltsUFM (spillStoreLoad stats))
-
+        = pprUFM (spillStoreLoad stats)
+                 (vcat . map (\(r, s, l) -> ppr r <+> int s <+> int l))

compiler/nativeGen/RegAlloc/Graph/SpillCost.hs

@@ -153,7 +153,8 @@ chooseSpill
 chooseSpill info graph
  = let  cost    = spillCost_length info graph
         node    = minimumBy (\n1 n2 -> compare (cost $ nodeId n1) (cost $ nodeId n2))
-                $ eltsUFM $ graphMap graph
+                $ nonDetEltsUFM $ graphMap graph
+                -- See Note [Unique Determinism and code generation]
 
    in   nodeId node
 
@@ -241,7 +242,8 @@ lifeMapFromSpillCostInfo :: SpillCostInfo -> UniqFM (VirtualReg, Int)
 lifeMapFromSpillCostInfo info
         = listToUFM
         $ map (\(r, _, _, life) -> (r, (r, life)))
-        $ eltsUFM info
+        $ nonDetEltsUFM info
+        -- See Note [Unique Determinism and code generation]
 
 
 -- | Determine the degree (number of neighbors) of this node which

compiler/nativeGen/RegAlloc/Graph/Stats.hs

@@ -129,7 +129,7 @@ instance (Outputable statics, Outputable instr)
 
         $$ (if (not $ isNullUFM $ raCoalesced s)
                 then    text "#  Registers coalesced."
-                        $$ (pprUFMWithKeys (raCoalesced s) (vcat . map ppr))
+                        $$ pprUFMWithKeys (raCoalesced s) (vcat . map ppr)
                         $$ text ""
                 else empty)
 
@@ -160,7 +160,7 @@ instance (Outputable statics, Outputable instr)
 
         $$ (if (not $ isNullUFM $ raCoalesced s)
                 then    text "#  Registers coalesced."
-                        $$ (pprUFMWithKeys (raCoalesced s) (vcat . map ppr))
+                        $$ pprUFMWithKeys (raCoalesced s) (vcat . map ppr)
                         $$ text ""
                 else empty)
 
@@ -232,7 +232,7 @@ pprStatsLifetimes stats
 
    in   (  text "-- vreg-population-lifetimes"
         $$ text "--   (instruction_count, number_of_vregs_that_lived_that_long)"
-        $$ (vcat $ map ppr $ eltsUFM lifeBins)
+        $$ pprUFM lifeBins (vcat . map ppr)
         $$ text "\n")
 
 
@@ -240,7 +240,8 @@ binLifetimeCount :: UniqFM (VirtualReg, Int) -> UniqFM (Int, Int)
 binLifetimeCount fm
  = let  lifes   = map (\l -> (l, (l, 1)))
                 $ map snd
-                $ eltsUFM fm
+                $ nonDetEltsUFM fm
+                -- See Note [Unique Determinism and code generation]
 
    in   addListToUFM_C
                 (\(l1, c1) (_, c2) -> (l1, c1 + c2))
@@ -260,7 +261,7 @@ pprStatsConflict stats
 
    in   (  text "-- vreg-conflicts"
         $$ text "--   (conflict_count, number_of_vregs_that_had_that_many_conflicts)"
-        $$ (vcat $ map ppr $ eltsUFM confMap)
+        $$ pprUFM confMap (vcat . map ppr)
         $$ text "\n")
 
 
@@ -285,7 +286,8 @@ pprStatsLifeConflict stats graph
                                         , ppr $ sizeUniqSet (Color.nodeConflicts node)
                                         , ppr $ lifetime ])
                 $ map Color.nodeId
-                $ eltsUFM
+                $ nonDetEltsUFM
+                -- See Note [Unique Determinism and code generation]
                 $ Color.graphMap graph
 
    in   (  text "-- vreg-conflict-lifetime"

compiler/nativeGen/RegAlloc/Graph/TrivColorable.hs

@@ -59,7 +59,8 @@ accSqueeze
         -> UniqFM reg
         -> Int
 
-accSqueeze count maxCount squeeze ufm = acc count (eltsUFM ufm)
+accSqueeze count maxCount squeeze ufm = acc count (nonDetEltsUFM ufm)
+  -- See Note [Unique Determinism and code generation]
   where acc count [] = count
         acc count _ | count >= maxCount = count
         acc count (r:rs) = acc (count + squeeze r) rs

compiler/nativeGen/RegAlloc/Linear/Stats.hs

@@ -66,7 +66,8 @@ pprStats code statss
 
         spillTotals     = foldl' (zipWith (+))
                                 [0, 0, 0, 0, 0]
-                        $ eltsUFM spills
+                        $ nonDetEltsUFM spills
+                        -- See Note [Unique Determinism and code generation]
 
         -- count how many reg-reg-moves remain in the code
         moves           = sum $ map countRegRegMovesNat code

compiler/utils/GraphOps.hs

@@ -307,7 +307,8 @@ coalesceGraph' aggressive triv graph kkPairsAcc
  = let
         -- find all the nodes that have coalescence edges
         cNodes  = filter (\node -> not $ isEmptyUniqSet (nodeCoalesce node))
-                $ eltsUFM $ graphMap graph
+                $ nonDetEltsUFM $ graphMap graph
+                -- See Note [Unique Determinism and code generation]
 
         -- build a list of pairs of keys for node's we'll try and coalesce
         --      every pair of nodes will appear twice in this list
@@ -528,7 +529,8 @@ freezeAllInGraph
 freezeAllInGraph graph
         = foldr freezeNode graph
                 $ map nodeId
-                $ eltsUFM $ graphMap graph
+                $ nonDetEltsUFM $ graphMap graph
+                -- See Note [Unique Determinism and code generation]
 
 
 -- | Find all the nodes in the graph that meet some criteria
@@ -539,7 +541,8 @@ scanGraph
         -> [Node k cls color]
 
 scanGraph match graph
-        = filter match $ eltsUFM $ graphMap graph
+        = filter match $ nonDetEltsUFM $ graphMap graph
+          -- See Note [Unique Determinism and code generation]
 
 
 -- | validate the internal structure of a graph
@@ -557,10 +560,10 @@ validateGraph doc isColored graph
 
         -- Check that all edges point to valid nodes.
         | edges         <- unionManyUniqSets
-                                (  (map nodeConflicts       $ eltsUFM $ graphMap graph)
-                                ++ (map nodeCoalesce        $ eltsUFM $ graphMap graph))
+                                (  (map nodeConflicts       $ nonDetEltsUFM $ graphMap graph)
+                                ++ (map nodeCoalesce        $ nonDetEltsUFM $ graphMap graph))
 
-        , nodes         <- mkUniqSet $ map nodeId $ eltsUFM $ graphMap graph
+        , nodes         <- mkUniqSet $ map nodeId $ nonDetEltsUFM $ graphMap graph
         , badEdges      <- minusUniqSet edges nodes
         , not $ isEmptyUniqSet badEdges
         = pprPanic "GraphOps.validateGraph"
@@ -570,7 +573,8 @@ validateGraph doc isColored graph
 
         -- Check that no conflicting nodes have the same color
         | badNodes      <- filter (not . (checkNode graph))
-                        $ eltsUFM $ graphMap graph
+                        $ nonDetEltsUFM $ graphMap graph
+                           -- See Note [Unique Determinism and code generation]
         , not $ null badNodes
         = pprPanic "GraphOps.validateGraph"
                 (  text "Node has same color as one of it's conflicts"
@@ -581,7 +585,7 @@ validateGraph doc isColored graph
         --      check that all nodes have a color.
         | isColored
         , badNodes      <- filter (\n -> isNothing $ nodeColor n)
-                        $  eltsUFM $ graphMap graph
+                        $  nonDetEltsUFM $ graphMap graph
         , not $ null badNodes
         = pprPanic "GraphOps.validateGraph"
                 (  text "Supposably colored graph has uncolored nodes."
@@ -630,7 +634,8 @@ slurpNodeConflictCount graph
         $ map   (\node
                   -> let count  = sizeUniqSet $ nodeConflicts node
                      in  (count, (count, 1)))
-        $ eltsUFM
+        $ nonDetEltsUFM
+        -- See Note [Unique Determinism and code generation]
         $ graphMap graph
 
 

compiler/utils/GraphPpr.hs

@@ -25,7 +25,7 @@ dumpGraph
 
 dumpGraph graph
         =  text "Graph"
-        $$ (vcat $ map dumpNode $ eltsUFM $ graphMap graph)
+        $$ pprUFM (graphMap graph) (vcat . map dumpNode)
 
 dumpNode
         :: (Outputable k, Outputable color)
@@ -65,7 +65,8 @@ dotGraph
         -> Graph k cls color -> SDoc
 
 dotGraph colorMap triv graph
- = let  nodes   = eltsUFM $ graphMap graph
+ = let  nodes   = nonDetEltsUFM $ graphMap graph
+                  -- See Note [Unique Determinism and code generation]
    in   vcat
                 (  [ text "graph G {" ]
                 ++ map (dotNode colorMap triv) nodes