Super-monster patch implementing the new typechecker -- at last

[ghc-hetmet.git] / compiler / cmm / CmmSpillReload.hs

diff --git a/compiler/cmm/CmmSpillReload.hs b/compiler/cmm/CmmSpillReload.hs
index 1f88b76..c457383 100644 (file)
--- a/compiler/cmm/CmmSpillReload.hs
+++ b/compiler/cmm/CmmSpillReload.hs
@@ -1,3 +1,6 @@
+{-# OPTIONS_GHC -XNoMonoLocalBinds #-}
+-- Norman likes local bindings
+-- If this module lives on I'd like to get rid of this flag in due course
 
 module CmmSpillReload
   ( DualLive(..)
@@ -23,28 +26,31 @@ import ZipCfg
 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 }
 
@@ -64,7 +70,7 @@ changeRegs  f live = live { in_regs  = f (in_regs  live) }
 
 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)