+#if __GLASGOW_HASKELL__ >= 611
+{-# OPTIONS_GHC -XNoMonoLocalBinds #-}
+#endif
+-- Norman likes local bindings
+-- If this module lives on I'd like to get rid of this flag in due course
module CmmSpillReload
( DualLive(..)
import ZipCfgCmmRep
import ZipDataflow
-import Monad
+import Control.Monad
import Outputable hiding (empty)
import qualified Outputable as PP
import UniqSet
-import Maybe
+import Data.Maybe
import Prelude hiding (zip)
--- The point of this module is to insert spills and reloads to
--- establish the invariant that at a call (or at any proc point with
--- an established protocol) all live variables not expected in
--- registers are sitting on the stack. We use a backward analysis to
--- insert spills and reloads. It should be followed by a
--- forward transformation to sink reloads as deeply as possible, so as
--- to reduce register pressure.
-
--- A variable can be expected to be live in a register, live on the
--- stack, or both. This analysis ensures that spills and reloads are
--- inserted as needed to make sure that every live variable needed
--- after a call is available on the stack. Spills are pushed back to
--- their reaching definitions, but reloads are dropped wherever needed
--- and will have to be sunk by a later forward transformation.
+{- Note [Overview of spill/reload]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The point of this module is to insert spills and reloads to
+establish the invariant that at a call (or at any proc point with
+an established protocol) all live variables not expected in
+registers are sitting on the stack. We use a backward analysis to
+insert spills and reloads. It should be followed by a
+forward transformation to sink reloads as deeply as possible, so as
+to reduce register pressure.
+
+A variable can be expected to be live in a register, live on the
+stack, or both. This analysis ensures that spills and reloads are
+inserted as needed to make sure that every live variable needed
+after a call is available on the stack. Spills are pushed back to
+their reaching definitions, but reloads are dropped wherever needed
+and will have to be sunk by a later forward transformation.
+-}
data DualLive = DualLive { on_stack :: RegSet, in_regs :: RegSet }
dualLiveLattice :: DataflowLattice DualLive
dualLiveLattice =
- DataflowLattice "variables live in registers and on stack" empty add True
+ DataflowLattice "variables live in registers and on stack" empty add False
where empty = DualLive emptyRegSet emptyRegSet
-- | compute in the Tx monad to track whether anything has changed
add new old = do stack <- add1 (on_stack new) (on_stack old)