[project @ 2005-01-12 16:33:54 by simonmar]

Fix a bug in mk_switch.

diff --git a/ghc/compiler/codeGen/CgUtils.hs b/ghc/compiler/codeGen/CgUtils.hs
index a8e9c39..414e90a 100644 (file)
--- a/ghc/compiler/codeGen/CgUtils.hs
+++ b/ghc/compiler/codeGen/CgUtils.hs
@@ -405,11 +405,15 @@ mk_switch tag_expr branches mb_deflt lo_tag hi_tag
                find_branch :: ConTagZ -> Maybe BlockId
                find_branch i = assocDefault mb_deflt tagged_blk_ids i
 
-               arms = [ find_branch (i+lo_tag) | i <- [0..n_tags-1]]
+               -- NB. we have eliminated impossible branches at
+               -- either end of the range (see below), so the first
+               -- tag of a real branch is real_lo_tag (not lo_tag).
+               arms = [ find_branch i | i <- [real_lo_tag..real_hi_tag]]
 
-               switch_stmt = CmmSwitch (cmmOffset tag_expr (- lo_tag)) arms
+               switch_stmt = CmmSwitch (cmmOffset tag_expr (- real_lo_tag)) arms
 
-       ; return (oneCgStmt switch_stmt)
+       ; ASSERT(not (all isNothing arms)) 
+         return (oneCgStmt switch_stmt)
        }
 
   -- if we can knock off a bunch of default cases with one if, then do so