From: simonmar <unknown>
Date: Tue, 22 Feb 2005 10:58:22 +0000 (+0000)
Subject: [project @ 2005-02-22 10:58:22 by simonmar]
X-Git-Tag: Initial_conversion_from_CVS_complete~1042
X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=commitdiff_plain;h=90334ab3c0c841d466671a416763989d169d4877

[project @ 2005-02-22 10:58:22 by simonmar]
emitSwitch: if we're compiling via C, then always generate a switch
rather than an if-tree.  This should work around brokenness in older
versions of GCC.
---

diff --git a/ghc/compiler/codeGen/CgUtils.hs b/ghc/compiler/codeGen/CgUtils.hs
index 9a99bfd..c8cae4b 100644
--- a/ghc/compiler/codeGen/CgUtils.hs
+++ b/ghc/compiler/codeGen/CgUtils.hs
@@ -52,7 +52,7 @@ import CLabel		( CLabel, mkStringLitLabel )
 import Digraph		( SCC(..), stronglyConnComp )
 import ListSetOps	( assocDefault )
 import Util		( filterOut, sortLe )
-import CmdLineOpts	( DynFlags )
+import CmdLineOpts	( DynFlags(..), HscTarget(..) )
 import FastString	( LitString, FastString, unpackFS )
 import Outputable
 
@@ -358,8 +358,12 @@ emitSwitch tag_expr branches mb_deflt lo_tag hi_tag
 		  Nothing    -> return Nothing
 		  Just stmts -> do id <- forkCgStmts stmts; return (Just id)
 
+	; dflags <- getDynFlags
+	; let via_C | HscC <- hscTarget dflags = True
+		    | otherwise                = False
+
 	; stmts <- mk_switch tag_expr (sortLe le branches) 
-			mb_deflt_id lo_tag hi_tag
+			mb_deflt_id lo_tag hi_tag via_C
 	; emitCgStmts stmts
 	}
   where
@@ -367,17 +371,17 @@ emitSwitch tag_expr branches mb_deflt lo_tag hi_tag
 
 
 mk_switch :: CmmExpr -> [(ConTagZ, CgStmts)]
-	  -> Maybe BlockId -> ConTagZ -> ConTagZ
+	  -> Maybe BlockId -> ConTagZ -> ConTagZ -> Bool
 	  -> FCode CgStmts
 
 -- SINGLETON TAG RANGE: no case analysis to do
-mk_switch tag_expr [(tag,stmts)] _ lo_tag hi_tag
+mk_switch tag_expr [(tag,stmts)] _ lo_tag hi_tag via_C
   | lo_tag == hi_tag
   = ASSERT( tag == lo_tag )
     return stmts
 
 -- SINGLETON BRANCH, NO DEFUALT: no case analysis to do
-mk_switch tag_expr [(tag,stmts)] Nothing lo_tag hi_tag
+mk_switch tag_expr [(tag,stmts)] Nothing lo_tag hi_tag via_C
   = return stmts
 	-- The simplifier might have eliminated a case
 	-- 	 so we may have e.g. case xs of 
@@ -386,7 +390,7 @@ mk_switch tag_expr [(tag,stmts)] Nothing lo_tag hi_tag
 	-- can't happen, so no need to test
 
 -- SINGLETON BRANCH: one equality check to do
-mk_switch tag_expr [(tag,stmts)] (Just deflt) lo_tag hi_tag
+mk_switch tag_expr [(tag,stmts)] (Just deflt) lo_tag hi_tag via_C
   = return (CmmCondBranch cond deflt `consCgStmt` stmts)
   where
     cond  =  cmmNeWord tag_expr (CmmLit (mkIntCLit tag))
@@ -397,9 +401,17 @@ mk_switch tag_expr [(tag,stmts)] (Just deflt) lo_tag hi_tag
 -- the branches is the tag 0, because comparing '== 0' is likely to be
 -- more efficient than other kinds of comparison.
 
--- DENSE TAG RANGE: use a switch statment
-mk_switch tag_expr branches mb_deflt lo_tag hi_tag
-  | use_switch 	-- Use a switch
+-- DENSE TAG RANGE: use a switch statment.
+--
+-- We also use a switch uncoditionally when compiling via C, because
+-- this will get emitted as a C switch statement and the C compiler
+-- should do a good job of optimising it.  Also, older GCC versions
+-- (2.95 in particular) have problems compiling the complicated
+-- if-trees generated by this code, so compiling to a switch every
+-- time works around that problem.
+--
+mk_switch tag_expr branches mb_deflt lo_tag hi_tag via_C
+  | use_switch || via_C 	-- Use a switch
   = do	{ branch_ids <- mapM forkCgStmts (map snd branches)
 	; let 
 		tagged_blk_ids = zip (map fst branches) (map Just branch_ids)
@@ -423,7 +435,8 @@ mk_switch tag_expr branches mb_deflt lo_tag hi_tag
   = do { (assign_tag, tag_expr') <- assignTemp' tag_expr
        ; let cond = cmmULtWord tag_expr' (CmmLit (mkIntCLit lowest_branch))
 	     branch = CmmCondBranch cond deflt
-       ; stmts <- mk_switch tag_expr' branches mb_deflt lowest_branch hi_tag
+       ; stmts <- mk_switch tag_expr' branches mb_deflt 
+			lowest_branch hi_tag via_C
        ; return (assign_tag `consCgStmt` (branch `consCgStmt` stmts))
        }
 
@@ -431,15 +444,18 @@ mk_switch tag_expr branches mb_deflt lo_tag hi_tag
   = do { (assign_tag, tag_expr') <- assignTemp' tag_expr
        ; let cond = cmmUGtWord tag_expr' (CmmLit (mkIntCLit highest_branch))
 	     branch = CmmCondBranch cond deflt
-       ; stmts <- mk_switch tag_expr' branches mb_deflt lo_tag highest_branch
+       ; stmts <- mk_switch tag_expr' branches mb_deflt 
+			lo_tag highest_branch via_C
        ; return (assign_tag `consCgStmt` (branch `consCgStmt` stmts))
        }
 
   | otherwise	-- Use an if-tree
   = do	{ (assign_tag, tag_expr') <- assignTemp' tag_expr
 		-- To avoid duplication
-	; lo_stmts <- mk_switch tag_expr' lo_branches mb_deflt lo_tag (mid_tag-1)
-	; hi_stmts <- mk_switch tag_expr' hi_branches mb_deflt mid_tag hi_tag
+	; lo_stmts <- mk_switch tag_expr' lo_branches mb_deflt 
+				lo_tag (mid_tag-1) via_C
+	; hi_stmts <- mk_switch tag_expr' hi_branches mb_deflt 
+				mid_tag hi_tag via_C
 	; lo_id <- forkCgStmts lo_stmts
 	; let cond = cmmULtWord tag_expr' (CmmLit (mkIntCLit mid_tag))
 	      branch_stmt = CmmCondBranch cond lo_id