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|
{-# LANGUAGE GADTs #-}
{-# OPTIONS_GHC -fno-warn-warnings-deprecations #-}
module CmmLive
( CmmLive
, cmmLiveness
, liveLattice
, noLiveOnEntry, xferLive, gen, kill, gen_kill
, removeDeadAssignments
)
where
import UniqSupply
import BlockId
import Cmm
import CmmUtils
import PprCmmExpr ()
import Hoopl
import Maybes
import Outputable
-----------------------------------------------------------------------------
-- Calculating what variables are live on entry to a basic block
-----------------------------------------------------------------------------
-- | The variables live on entry to a block
type CmmLive = RegSet
-- | The dataflow lattice
liveLattice :: DataflowLattice CmmLive
liveLattice = DataflowLattice "live LocalReg's" emptyRegSet add
where add _ (OldFact old) (NewFact new) =
(changeIf $ sizeRegSet join > sizeRegSet old, join)
where !join = plusRegSet old new
-- | A mapping from block labels to the variables live on entry
type BlockEntryLiveness = BlockEnv CmmLive
-----------------------------------------------------------------------------
-- | Calculated liveness info for a CmmGraph
-----------------------------------------------------------------------------
cmmLiveness :: CmmGraph -> BlockEntryLiveness
cmmLiveness graph =
check $ dataflowAnalBwd graph [] $ analBwd liveLattice xferLive
where entry = g_entry graph
check facts = noLiveOnEntry entry
(expectJust "check" $ mapLookup entry facts) facts
-- | On entry to the procedure, there had better not be any LocalReg's live-in.
noLiveOnEntry :: BlockId -> CmmLive -> a -> a
noLiveOnEntry bid in_fact x =
if nullRegSet in_fact then x
else pprPanic "LocalReg's live-in to graph" (ppr bid <+> ppr in_fact)
-- | The transfer equations use the traditional 'gen' and 'kill'
-- notations, which should be familiar from the Dragon Book.
gen :: UserOfLocalRegs a => a -> RegSet -> RegSet
gen a live = foldRegsUsed extendRegSet live a
kill :: DefinerOfLocalRegs a => a -> RegSet -> RegSet
kill a live = foldRegsDefd deleteFromRegSet live a
gen_kill :: (DefinerOfLocalRegs a, UserOfLocalRegs a)
=> a -> CmmLive -> CmmLive
gen_kill a = gen a . kill a
-- | The transfer function
xferLive :: BwdTransfer CmmNode CmmLive
xferLive = mkBTransfer3 fst mid lst
where fst _ f = f
mid :: CmmNode O O -> CmmLive -> CmmLive
mid n f = gen_kill n f
lst :: CmmNode O C -> FactBase CmmLive -> CmmLive
lst n f = gen_kill n $ joinOutFacts liveLattice n f
-----------------------------------------------------------------------------
-- Removing assignments to dead variables
-----------------------------------------------------------------------------
removeDeadAssignments :: CmmGraph -> UniqSM (CmmGraph, BlockEnv CmmLive)
removeDeadAssignments g =
dataflowPassBwd g [] $ analRewBwd liveLattice xferLive rewrites
where rewrites = mkBRewrite3 nothing middle nothing
-- SDM: no need for deepBwdRw here, we only rewrite to empty
-- Beware: deepBwdRw with one polymorphic function seems more
-- reasonable here, but GHC panics while compiling, see bug
-- #4045.
middle :: CmmNode O O -> Fact O CmmLive -> CmmReplGraph O O
middle (CmmAssign (CmmLocal reg') _) live
| not (reg' `elemRegSet` live)
= return $ Just emptyGraph
-- XXX maybe this should be somewhere else...
middle (CmmAssign lhs (CmmReg rhs)) _ | lhs == rhs
= return $ Just emptyGraph
middle (CmmStore lhs (CmmLoad rhs _)) _ | lhs == rhs
= return $ Just emptyGraph
middle _ _ = return Nothing
nothing :: CmmNode e x -> Fact x CmmLive -> CmmReplGraph e x
nothing _ _ = return Nothing
|
