[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 (file)
--- 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