Improve GraphColor.colorScan

[ghc-hetmet.git] / compiler / nativeGen / GraphColor.hs

diff --git a/compiler/nativeGen/GraphColor.hs b/compiler/nativeGen/GraphColor.hs
index c60c12d..c6aea25 100644 (file)
--- a/compiler/nativeGen/GraphColor.hs
+++ b/compiler/nativeGen/GraphColor.hs
@@ -56,14 +56,16 @@ colorGraph colors triv spill graph0
 
        -- run the scanner to slurp out all the trivially colorable nodes
        (ksTriv, ksProblems)
-               = colorScan colors triv spill [] emptyUniqSet graph_coalesced
+               = colorScan triv spill graph_coalesced
  
        -- color the trivially colorable nodes
+       --      as the keys were added to the front of the list while they were scanned,
+       --      this colors them in the reverse order they were found, as required by the algorithm.
        (graph_triv, ksNoTriv)
                = assignColors colors graph_coalesced ksTriv
 
        -- try and color the problem nodes
-       (graph_prob, ksNoColor) = assignColors colors graph_triv (uniqSetToList ksProblems)
+       (graph_prob, ksNoColor) = assignColors colors graph_triv ksProblems
 
        -- if the trivially colorable nodes didn't color then something is wrong
        --      with the provided triv function.
@@ -79,6 +81,90 @@ colorGraph colors triv spill graph0
                , mkUniqSet ksNoColor
                , listToUFM rsCoalesce)
        
+
+-- | Scan through the conflict graph separating out trivially colorable and
+--     potentially uncolorable (problem) nodes.
+--
+--     Checking whether a node is trivially colorable or not is a resonably expensive operation,
+--     so after a triv node is found and removed from the graph it's no good to return to the 'start'
+--     of the graph and recheck a bunch of nodes that will probably still be non-trivially colorable.
+--
+--     To ward against this, during each pass through the graph we collect up a list of triv nodes
+--     that were found, and only remove them once we've finished the pass. The more nodes we can delete
+--     at once the more likely it is that nodes we've already checked will become trivially colorable
+--     for the next pass.
+--
+colorScan
+       :: ( Uniquable k, Uniquable cls, Uniquable color)
+       => Triv k cls color             -- ^ fn to decide whether a node is trivially colorable
+       -> (Graph k cls color -> k)     -- ^ fn to choose a node to potentially leave uncolored if nothing is trivially colorable.
+       -> Graph k cls color            -- ^ the graph to scan
+       -> ([k], [k])                   --  triv colorable, problem nodes
+
+
+colorScan triv spill graph
+       = colorScan' triv spill graph
+               []      []
+               []
+               (eltsUFM $ graphMap graph)
+
+-- we've reached the end of the candidates list
+colorScan' triv spill graph
+       ksTriv  ksTrivFound
+       ksSpill
+       []
+
+       -- if the graph is empty then we're done
+       | isNullUFM $ graphMap graph
+       = (ksTrivFound ++ ksTriv, ksSpill)
+
+       -- if we haven't found a trivially colorable node then we'll have to
+       --      choose a spill candidate and leave it uncolored
+       | []            <- ksTrivFound
+       , kSpill        <- spill graph                  -- choose a spill candiate
+       , graph'        <- delNode kSpill graph         -- remove it from the graph
+       , nsRest'       <- eltsUFM $ graphMap graph'    -- graph has changed, so get new node list
+
+       = colorScan' triv spill graph'
+               ksTriv ksTrivFound
+               (kSpill : ksSpill)
+               nsRest'
+
+       -- we're at the end of the candidates list but we've found some triv nodes
+       --      along the way. We can delete them from the graph and go back for more.
+       | graph'        <- foldr delNode graph ksTrivFound
+       , nsRest'       <- eltsUFM $ graphMap graph'
+
+       = colorScan' triv spill graph'
+               (ksTrivFound ++ ksTriv) []
+               ksSpill
+               nsRest'
+
+-- check if the current node is triv colorable
+colorScan' triv spill graph
+       ksTriv  ksTrivFound
+       ksSpill
+       (node : nsRest)
+
+       -- node is trivially colorable
+       --      add it to the found nodes list and carry on.
+       | k     <- nodeId node
+       , triv (nodeClass node) (nodeConflicts node) (nodeExclusions node)
+
+       = colorScan' triv spill graph
+               ksTriv  (k : ksTrivFound)
+               ksSpill
+               nsRest
+
+       -- node wasn't trivially colorable, skip over it and look in the rest of the list
+       | otherwise
+       = colorScan' triv spill graph
+               ksTriv ksTrivFound
+               ksSpill
+               nsRest
+
+{- -- This is cute and easy to understand, but too slow.. BL 2007/09
+
 colorScan colors triv spill safe prob graph
 
        -- empty graphs are easy to color.
@@ -100,7 +186,8 @@ colorScan colors triv spill safe prob graph
        | k             <- spill graph
        = colorScan colors triv spill
                safe (addOneToUniqSet prob k) (delNode k graph)
-               
+-}
+
 
 -- | Try to assign a color to all these nodes.