NCG: Linear-reg-alloc: A few small implemenation tweaks.

Removed an intermediate list via a fold.
realRegsAlias: Manually inlined the list functions to get better code.
Linear.hs added a bang somewhere.

3 files changed, 40 insertions, 25 deletions

diff --git a/compiler/GHC/CmmToAsm/Reg/Linear.hs b/compiler/GHC/CmmToAsm/Reg/Linear.hs
index a9a4545f62..021c909a52 100644
--- a/compiler/GHC/CmmToAsm/Reg/Linear.hs
+++ b/compiler/GHC/CmmToAsm/Reg/Linear.hs
@@ -677,29 +677,30 @@ saveClobberedTemps [] _
 saveClobberedTemps clobbered dying
  = do
         assig   <- getAssigR :: RegM freeRegs (UniqFM Reg Loc)
-        -- Unique represents the VirtualReg
-        let to_spill :: [(Unique, RealReg)]
-            to_spill
-                = [ (temp,reg)
-                        | (temp, InReg reg) <- nonDetUFMToList assig
-                        -- This is non-deterministic but we do not
-                        -- currently support deterministic code-generation.
-                        -- See Note [Unique Determinism and code generation]
-                        , any (realRegsAlias reg) clobbered
-                        , temp `notElem` map getUnique dying  ]
-
-        (instrs,assig') <- clobber assig [] to_spill
+        (assig',instrs) <- nonDetStrictFoldUFM_DirectlyM maybe_spill (assig,[]) assig
         setAssigR assig'
         return $ -- mkComment (text "<saveClobberedTemps>") ++
                  instrs
 --              ++ mkComment (text "</saveClobberedTemps>")
    where
-     -- See Note [UniqFM and the register allocator]
-     clobber :: RegMap Loc -> [instr] -> [(Unique,RealReg)] -> RegM freeRegs ([instr], RegMap Loc)
-     clobber assig instrs []
-            = return (instrs, assig)
+     -- Unique represents the VirtualReg
+     -- Here we separate the cases which we do want to spill from these we don't.
+     maybe_spill :: Unique -> (RegMap Loc,[instr]) -> (Loc) -> RegM freeRegs (RegMap Loc,[instr])
+     maybe_spill !temp !(assig,instrs) !loc =
+        case loc of
+                -- This is non-deterministic but we do not
+                -- currently support deterministic code-generation.
+                -- See Note [Unique Determinism and code generation]
+                InReg reg
+                    | any (realRegsAlias reg) clobbered
+                    , temp `notElem` map getUnique dying
+                    -> clobber temp (assig,instrs) (reg)
+                _ -> return (assig,instrs)
 
-     clobber assig instrs ((temp, reg) : rest)
+
+     -- See Note [UniqFM and the register allocator]
+     clobber :: Unique -> (RegMap Loc,[instr]) -> (RealReg) -> RegM freeRegs (RegMap Loc,[instr])
+     clobber temp (assig,instrs) (reg)
        = do platform <- getPlatform
 
             freeRegs <- getFreeRegsR
@@ -718,7 +719,7 @@ saveClobberedTemps clobbered dying
                   let instr = mkRegRegMoveInstr platform
                                   (RegReal reg) (RegReal my_reg)
 
-                  clobber new_assign (instr : instrs) rest
+                  return (new_assign,(instr : instrs))
 
               -- (2) no free registers: spill the value
               [] -> do
@@ -729,7 +730,8 @@ saveClobberedTemps clobbered dying
 
                   let new_assign  = addToUFM_Directly assig temp (InBoth reg slot)
 
-                  clobber new_assign (spill ++ instrs) rest
+                  return (new_assign, (spill ++ instrs))
+
 
 
 
diff --git a/compiler/GHC/Platform/Reg.hs b/compiler/GHC/Platform/Reg.hs
index 5edd39df51..8203b9bbea 100644
--- a/compiler/GHC/Platform/Reg.hs
+++ b/compiler/GHC/Platform/Reg.hs
@@ -34,7 +34,6 @@ import GHC.Utils.Panic
 import GHC.Types.Unique
 import GHC.Builtin.Uniques
 import GHC.Platform.Reg.Class
-import Data.List (intersect)
 
 -- | An identifier for a primitive real machine register.
 type RegNo
@@ -173,8 +172,17 @@ regNosOfRealReg rr
 
 
 realRegsAlias :: RealReg -> RealReg -> Bool
-realRegsAlias rr1 rr2
-        = not $ null $ intersect (regNosOfRealReg rr1) (regNosOfRealReg rr2)
+realRegsAlias rr1 rr2 =
+    -- used to be `not $ null $ intersect (regNosOfRealReg rr1) (regNosOfRealReg rr2)`
+    -- but that resulted in some gnarly, gnarly, allocating code. So we manually
+    -- write out all the cases which gives us nice non-allocating code.
+    case rr1 of
+        RealRegSingle r1 ->
+            case rr2 of RealRegPair r2 r3 -> r1 == r2 || r1 == r3
+                        RealRegSingle r2 -> r1 == r2
+        RealRegPair r1 r2 ->
+            case rr2 of RealRegPair r3 r4 -> r1 == r3 || r1 == r4 || r2 == r3 || r2 == r4
+                        RealRegSingle r3 -> r1 == r3 || r2 == r3
 
 --------------------------------------------------------------------------------
 -- | A register, either virtual or real
diff --git a/compiler/GHC/Types/Unique/FM.hs b/compiler/GHC/Types/Unique/FM.hs
index 46b8643f76..a293c6bb10 100644
--- a/compiler/GHC/Types/Unique/FM.hs
+++ b/compiler/GHC/Types/Unique/FM.hs
@@ -63,7 +63,7 @@ module GHC.Types.Unique.FM (
         intersectUFM_C,
         disjointUFM,
         equalKeysUFM,
-        nonDetStrictFoldUFM, foldUFM, nonDetStrictFoldUFM_Directly,
+        nonDetStrictFoldUFM, foldUFM, nonDetStrictFoldUFM_DirectlyM,
         anyUFM, allUFM, seqEltsUFM,
         mapUFM, mapUFM_Directly,
         elemUFM, elemUFM_Directly,
@@ -402,11 +402,16 @@ nonDetKeysUFM (UFM m) = map getUnique $ M.keys m
 nonDetStrictFoldUFM :: (elt -> a -> a) -> a -> UniqFM key elt -> a
 nonDetStrictFoldUFM k z (UFM m) = M.foldl' (flip k) z m
 
+-- | In essence foldM
 -- See Note [Deterministic UniqFM] to learn about nondeterminism.
 -- If you use this please provide a justification why it doesn't introduce
 -- nondeterminism.
-nonDetStrictFoldUFM_Directly:: (Unique -> elt -> a -> a) -> a -> UniqFM key elt -> a
-nonDetStrictFoldUFM_Directly k z (UFM m) = M.foldlWithKey' (\z' i x -> k (getUnique i) x z') z m
+{-# INLINE nonDetStrictFoldUFM_DirectlyM #-} -- Allow specialization
+nonDetStrictFoldUFM_DirectlyM :: (Monad m) => (Unique -> b -> elt -> m b) -> b -> UniqFM key elt -> m b
+nonDetStrictFoldUFM_DirectlyM f z0 (UFM xs) = M.foldrWithKey c return xs z0
+  -- See Note [List fusion and continuations in 'c']
+  where c u x k z = f (getUnique u) z x >>= k
+        {-# INLINE c #-}
 
 -- See Note [Deterministic UniqFM] to learn about nondeterminism.
 -- If you use this please provide a justification why it doesn't introduce