diff options
| -rw-r--r-- | compiler/cmm/CmmSwitch.hs | 6 |
1 files changed, 4 insertions, 2 deletions
diff --git a/compiler/cmm/CmmSwitch.hs b/compiler/cmm/CmmSwitch.hs index 95e57c70af..09abec6f8b 100644 --- a/compiler/cmm/CmmSwitch.hs +++ b/compiler/cmm/CmmSwitch.hs @@ -88,7 +88,8 @@ minJumpTableOffset = 2 -- We use an Integer for the keys the map so that it can be used in switches on -- unsigned as well as signed integers. -- --- The map must not be empty. +-- The map may be empty (we prune out-of-range branches here, so it could be us +-- emptying it). -- -- Before code generation, the table needs to be brought into a form where all -- entries are non-negative, so that it can be compiled into a jump table. @@ -270,6 +271,7 @@ createSwitchPlan (SwitchTargets signed mbdef range m) = --- Step 1: Splitting at large holes --- splitAtHoles :: Integer -> M.Map Integer a -> [M.Map Integer a] +splitAtHoles _ m | M.null m = [] splitAtHoles holeSize m = map (\range -> restrictMap range m) nonHoles where holes = filter (\(l,h) -> h - l > holeSize) $ zip (M.keys m) (tail (M.keys m)) @@ -282,7 +284,7 @@ splitAtHoles holeSize m = map (\range -> restrictMap range m) nonHoles --- Step 2: Avoid small jump tables --- -- We do not want jump tables below a certain size. This breaks them up --- (into singleton maps, for now) +-- (into singleton maps, for now). breakTooSmall :: M.Map Integer a -> [M.Map Integer a] breakTooSmall m | M.size m > minJumpTableSize = [m] |