X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2FcodeGen%2FCgUtils.hs;h=804aeabd13fe95c139ccc925afd877a0ef746b08;hb=e48e1322ec737af04e276bd4f73e722e80b0d74d;hp=21e6d0850ccbd40251908df954c41212ba291092;hpb=61d2625ae2e6a4cdae2ffc92df828905e81c24cc;p=ghc-hetmet.git

diff --git a/compiler/codeGen/CgUtils.hs b/compiler/codeGen/CgUtils.hs
index 21e6d08..804aeab 100644
--- a/compiler/codeGen/CgUtils.hs
+++ b/compiler/codeGen/CgUtils.hs
@@ -2,7 +2,7 @@
 --
 -- Code generator utilities; mostly monadic
 --
--- (c) The University of Glasgow 2004
+-- (c) The University of Glasgow 2004-2006
 --
 -----------------------------------------------------------------------------
 
@@ -34,32 +34,29 @@ module CgUtils (
 #include "HsVersions.h"
 
 import CgMonad
-import TyCon		( TyCon, tyConName )
-import Id		( Id )
-import Constants	( wORD_SIZE )
-import SMRep		( CgRep, StgWord, hALF_WORD_SIZE_IN_BITS, ByteOff,
-			  WordOff, idCgRep )
+import TyCon
+import Id
+import Constants
+import SMRep
 import PprCmm		( {- instances -} )
 import Cmm
 import CLabel
 import CmmUtils
-import MachOp		( MachRep(..), wordRep, MachOp(..),  MachHint(..),
-			  mo_wordOr, mo_wordAnd, mo_wordNe, mo_wordEq,
-			  mo_wordULt, mo_wordUGt, mo_wordUGe, machRepByteWidth )
-import ForeignCall	( CCallConv(..) )
-import Literal		( Literal(..) )
-import Digraph		( SCC(..), stronglyConnComp )
-import ListSetOps	( assocDefault )
-import Util		( filterOut, sortLe )
-import DynFlags		( DynFlags(..), HscTarget(..) )
-import FastString	( LitString, bytesFS )
-import PackageConfig	( PackageId )
+import MachOp
+import ForeignCall
+import Literal
+import Digraph
+import ListSetOps
+import Util
+import DynFlags
+import FastString
+import PackageConfig
 import Outputable
 
-import Char		( ord )
-import DATA_BITS
-import DATA_WORD	( Word8 )
-import Maybe		( isNothing )
+import Data.Char
+import Data.Bits
+import Data.Word
+import Data.Maybe
 
 -------------------------------------------------------------------------
 --
@@ -477,15 +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