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

7 files changed, 23 insertions, 15 deletions

diff --git a/compiler/nativeGen/AsmCodeGen.hs b/compiler/nativeGen/AsmCodeGen.hs
index 094a9085be..46c6fa4763 100644
--- a/compiler/nativeGen/AsmCodeGen.hs
+++ b/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)
 
diff --git a/compiler/nativeGen/RegAlloc/Graph/Main.hs b/compiler/nativeGen/RegAlloc/Graph/Main.hs
index f7b3d0179d..0b10f3c1e3 100644
--- a/compiler/nativeGen/RegAlloc/Graph/Main.hs
+++ b/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
diff --git a/compiler/nativeGen/RegAlloc/Graph/Spill.hs b/compiler/nativeGen/RegAlloc/Graph/Spill.hs
index 9c3ccae315..a1d46cbc1b 100644
--- a/compiler/nativeGen/RegAlloc/Graph/Spill.hs
+++ b/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))
diff --git a/compiler/nativeGen/RegAlloc/Graph/SpillCost.hs b/compiler/nativeGen/RegAlloc/Graph/SpillCost.hs
index beffde97bb..198be622e1 100644
--- a/compiler/nativeGen/RegAlloc/Graph/SpillCost.hs
+++ b/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
diff --git a/compiler/nativeGen/RegAlloc/Graph/Stats.hs b/compiler/nativeGen/RegAlloc/Graph/Stats.hs
index cfd8f83122..9a8d0068ff 100644
--- a/compiler/nativeGen/RegAlloc/Graph/Stats.hs
+++ b/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"
diff --git a/compiler/nativeGen/RegAlloc/Graph/TrivColorable.hs b/compiler/nativeGen/RegAlloc/Graph/TrivColorable.hs
index 4bbf5d4c88..a40bec16e4 100644
--- a/compiler/nativeGen/RegAlloc/Graph/TrivColorable.hs
+++ b/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
diff --git a/compiler/nativeGen/RegAlloc/Linear/Stats.hs b/compiler/nativeGen/RegAlloc/Linear/Stats.hs
index c55df6bee8..71dedaeb55 100644
--- a/compiler/nativeGen/RegAlloc/Linear/Stats.hs
+++ b/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