X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2FcodeGen%2FCgUtils.hs;h=804aeabd13fe95c139ccc925afd877a0ef746b08;hb=7ac266d097639620e4fea22c40450c8d7822f5fb;hp=ab39080c16ed325afb9b0db2cedc5e1213f0bc0e;hpb=49c98d143c382a1341e1046f5ca00819a25691ba;p=ghc-hetmet.git

diff --git a/compiler/codeGen/CgUtils.hs b/compiler/codeGen/CgUtils.hs
index ab39080..804aeab 100644
--- a/compiler/codeGen/CgUtils.hs
+++ b/compiler/codeGen/CgUtils.hs
@@ -474,15 +474,18 @@ mk_switch tag_expr branches mb_deflt lo_tag hi_tag via_C
   where
     use_switch 	 = {- pprTrace "mk_switch" (
 			ppr tag_expr <+> text "n_tags:" <+> int n_tags <+>
+                        text "branches:" <+> ppr (map fst branches) <+>
 			text "n_branches:" <+> int n_branches <+>
-			text "lo_tag: " <+> int lo_tag <+>
-			text "hi_tag: " <+> int hi_tag <+>
-			text "real_lo_tag: " <+> int real_lo_tag <+>
-			text "real_hi_tag: " <+> int real_hi_tag) $ -}
+			text "lo_tag:" <+> int lo_tag <+>
+			text "hi_tag:" <+> int hi_tag <+>
+			text "real_lo_tag:" <+> int real_lo_tag <+>
+			text "real_hi_tag:" <+> int real_hi_tag) $ -}
 		   ASSERT( n_branches > 1 && n_tags > 1 ) 
-		   n_tags > 2 && (small || dense || via_C)
-		 -- a 2-branch switch always turns into an if.
-    small      	 = n_tags <= 4
+		   n_tags > 2 && (via_C || (dense && big_enough))
+		 -- up to 4 branches we use a decision tree, otherwise
+                 -- a switch (== jump table in the NCG).  This seems to be
+                 -- optimal, and corresponds with what gcc does.
+    big_enough 	 = n_branches > 4
     dense      	 = n_branches > (n_tags `div` 2)
     n_branches   = length branches