X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Futils%2FGraphColor.hs;h=8e7989dc8cd25dad20af42700c4d751aa3bfde0e;hb=b3ee146e56463e8b492bf7ba1ad95ba7d966ea8d;hp=bd777b775d213457212529d42fc03aa9bffb3475;hpb=6a347ffc34c0ded44c213e2a0217477f7b8196b9;p=ghc-hetmet.git

diff --git a/compiler/utils/GraphColor.hs b/compiler/utils/GraphColor.hs
index bd777b7..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,
@@ -39,6 +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 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.
@@ -49,14 +50,22 @@ colorGraph
 	   , UniqFM  k )		-- map of regs (r1 -> r2) that were coaleced
 	   				--	 r1 should be replaced by r2 in the source
 
-colorGraph iterative colors triv spill graph0
+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 True 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)