[project @ 2004-08-17 15:23:47 by simonpj]

[ghc-hetmet.git] / ghc / compiler / utils / Digraph.lhs

diff --git a/ghc/compiler/utils/Digraph.lhs b/ghc/compiler/utils/Digraph.lhs
index d8f6220..0eff6da 100644 (file)
--- a/ghc/compiler/utils/Digraph.lhs
+++ b/ghc/compiler/utils/Digraph.lhs
@@ -32,9 +32,7 @@ module Digraph(
 ------------------------------------------------------------------------------
 
 
-#define ARR_ELT                (COMMA)
-
-import Util    ( sortLt )
+import Util    ( sortLe )
 
 -- Extensions
 import MONAD_ST
@@ -80,7 +78,8 @@ stronglyConnComp
        => [(node, key, [key])]         -- The graph; its ok for the
                                        -- out-list to contain keys which arent
                                        -- a vertex key, they are ignored
-       -> [SCC node]
+       -> [SCC node]   -- Returned in topologically sorted order
+                       -- Later components depend on earlier ones, but not vice versa
 
 stronglyConnComp edges
   = map get_node (stronglyConnCompR edges)
@@ -101,8 +100,8 @@ stronglyConnCompR [] = []  -- added to avoid creating empty array in graphFromEd
 stronglyConnCompR edges
   = map decode forest
   where
-    (graph, vertex_fn) = graphFromEdges edges
-    forest            = scc graph
+    (graph, vertex_fn) = _scc_ "graphFromEdges" graphFromEdges edges
+    forest            = _scc_ "Digraph.scc" scc graph
     decode (Node v []) | mentions_itself v = CyclicSCC [vertex_fn v]
                       | otherwise         = AcyclicSCC (vertex_fn v)
     decode other = CyclicSCC (dec other [])
@@ -164,14 +163,16 @@ graphFromEdges edges
   where
     max_v                  = length edges - 1
     bounds          = (0,max_v) :: (Vertex, Vertex)
-    sorted_edges    = sortLt lt edges
+    sorted_edges    = let
+                        (_,k1,_) `le` (_,k2,_) = case k1 `compare` k2 of { GT -> False; other -> True }
+                     in
+                       sortLe le edges
     edges1         = zipWith (,) [0..] sorted_edges
 
     graph          = array bounds [(,) v (mapMaybe key_vertex ks) | (,) v (_,    _, ks) <- edges1]
     key_map        = array bounds [(,) v k                        | (,) v (_,    k, _ ) <- edges1]
     vertex_map     = array bounds edges1
 
-    (_,k1,_) `lt` (_,k2,_) = case k1 `compare` k2 of { LT -> True; other -> False }
 
     -- key_vertex :: key -> Maybe Vertex
     --         returns Nothing for non-interesting vertices
@@ -307,9 +308,6 @@ preorder (Node a ts) = a : preorderF ts
 preorderF           :: Forest a -> [a]
 preorderF ts         = concat (map preorder ts)
 
-preOrd :: Graph -> [Vertex]
-preOrd  = preorderF . dff
-
 tabulate        :: Bounds -> [Vertex] -> Table Int
 tabulate bnds vs = array bnds (zipWith (,) vs [1..])
 
@@ -363,12 +361,6 @@ scc g = dfs g (reverse (postOrd (transposeG g)))
 ------------------------------------------------------------
 
 \begin{code}
-tree              :: Bounds -> Forest Vertex -> Graph
-tree bnds ts       = buildG bnds (concat (map flat ts))
-                  where
-                    flat (Node v rs) = [ (v, w) | Node w us <- ts ] ++
-                                       concat (map flat ts)
-
 back              :: Graph -> Table Int -> Graph
 back g post        = mapT select g
  where select v ws = [ w | w <- ws, post!v < post!w ]