X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Futils%2FGraphColor.hs;h=8e7989dc8cd25dad20af42700c4d751aa3bfde0e;hb=f9cde00b2e1a078e433af81bf9021a96cc613976;hp=10852d4d9b2f703b095c97b03ddf28dcd4572d75;hpb=2381528a3b655af6becce8c8b130c63217992137;p=ghc-hetmet.git

diff --git a/compiler/utils/GraphColor.hs b/compiler/utils/GraphColor.hs
index 10852d4..8e7989d 100644
--- a/compiler/utils/GraphColor.hs
+++ b/compiler/utils/GraphColor.hs
@@ -1,9 +1,9 @@
+{-# OPTIONS -fno-warn-missing-signatures #-}
 
 -- | Graph Coloring.
 --	This is a generic graph coloring library, abstracted over the type of
 --	the node keys, nodes and colors.
 --
-{-# OPTIONS -fno-warn-missing-signatures #-}
 
 module GraphColor ( 
 	module GraphBase,
@@ -39,7 +39,7 @@ colorGraph
 	   , Eq color, Eq cls, Ord k
 	   , Outputable k, Outputable cls, Outputable color)
 	=> Bool				-- ^ whether to do iterative coalescing
-	-> Int				-- ^ how many times coloring has been called so far
+	-> Int				-- ^ how many times we've tried to color this graph so far.
 	-> UniqFM (UniqSet color)	-- ^ map of (node class -> set of colors available for this class).
 	-> 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.
@@ -52,12 +52,20 @@ colorGraph
 
 colorGraph iterative spinCount colors triv spill graph0
  = let
-	-- If we're not doing iterative coalescing then just do a conservative
-	--	coalescing stage at the front.
+	-- If we're not doing iterative coalescing then do an aggressive coalescing first time
+	--	around and then conservative coalescing for subsequent passes.
+	--
+	--	Aggressive coalescing is a quick way to get rid of many reg-reg moves. However, if
+	--	there is a lot of register pressure and we do it on every round then it can make the
+	--	graph less colorable and prevent the algorithm from converging in a sensible number
+	--	of cycles.
+	--
 	(graph_coalesced, kksCoalesce1)
-		= if not iterative
-			then coalesceGraph False triv graph0
-			else (graph0, [])
+	 = if iterative
+		then (graph0, [])
+		else if spinCount == 0
+			then coalesceGraph True  triv graph0
+			else coalesceGraph False triv graph0
 
  	-- run the scanner to slurp out all the trivially colorable nodes
 	--	(and do coalescing if iterative coalescing is enabled)
@@ -139,7 +147,7 @@ colorScan_spin iterative triv spill graph
 
 	-- if the graph is empty then we're done
 	| isNullUFM $ graphMap graph
-	= (ksTriv, ksSpill, kksCoalesce)
+	= (ksTriv, ksSpill, reverse kksCoalesce)
 
 	-- Simplify:
 	--	Look for trivially colorable nodes.
@@ -173,7 +181,7 @@ colorScan_spin iterative triv spill graph
 		--	go back to Simplify and see if this frees up more nodes to be trivially colorable.
 		(graph2, kksCoalesceFound @(_:_))
 		 -> colorScan_spin iterative triv spill graph2
-			ksTriv ksSpill (kksCoalesceFound ++ kksCoalesce)
+			ksTriv ksSpill (reverse kksCoalesceFound ++ kksCoalesce)
 
 		-- Freeze:
 		-- nothing could be coalesced (or was triv),