Commit 8f8d1ebf authored by Simon Marlow's avatar Simon Marlow
Browse files

extract some of the generic C-- optimisations from the NCG

parent 60905d44
......@@ -22,6 +22,7 @@ import NCGMonad
import PositionIndependentCode
import Cmm
import CmmOpt ( cmmMiniInline, cmmMachOpFold )
import PprCmm ( pprStmt, pprCmms )
import MachOp
import CLabel ( CLabel, mkSplitMarkerLabel, mkAsmTempLabel )
......@@ -396,7 +397,7 @@ Ideas for other things we could do (ToDo):
cmmToCmm :: CmmTop -> (CmmTop, [CLabel])
cmmToCmm top@(CmmData _ _) = (top, [])
cmmToCmm (CmmProc info lbl params blocks) = runCmmOpt $ do
blocks' <- mapM cmmBlockConFold (cmmPeep blocks)
blocks' <- mapM cmmBlockConFold (cmmMiniInline blocks)
return $ CmmProc info lbl params blocks'
newtype CmmOptM a = CmmOptM ([CLabel] -> (# a, [CLabel] #))
......@@ -535,391 +536,10 @@ cmmExprConFold isJumpTarget expr
other
-> return other
-- -----------------------------------------------------------------------------
-- MachOp constant folder
-- Now, try to constant-fold the MachOps. The arguments have already
-- been optimized and folded.
cmmMachOpFold
:: MachOp -- The operation from an CmmMachOp
-> [CmmExpr] -- The optimized arguments
-> CmmExpr
cmmMachOpFold op arg@[CmmLit (CmmInt x rep)]
= case op of
MO_S_Neg r -> CmmLit (CmmInt (-x) rep)
MO_Not r -> CmmLit (CmmInt (complement x) rep)
-- these are interesting: we must first narrow to the
-- "from" type, in order to truncate to the correct size.
-- The final narrow/widen to the destination type
-- is implicit in the CmmLit.
MO_S_Conv from to
| isFloatingRep to -> CmmLit (CmmFloat (fromInteger x) to)
| otherwise -> CmmLit (CmmInt (narrowS from x) to)
MO_U_Conv from to -> CmmLit (CmmInt (narrowU from x) to)
_ -> panic "cmmMachOpFold: unknown unary op"
-- Eliminate conversion NOPs
cmmMachOpFold (MO_S_Conv rep1 rep2) [x] | rep1 == rep2 = x
cmmMachOpFold (MO_U_Conv rep1 rep2) [x] | rep1 == rep2 = x
-- Eliminate nested conversions where possible
cmmMachOpFold conv_outer args@[CmmMachOp conv_inner [x]]
| Just (rep1,rep2,signed1) <- isIntConversion conv_inner,
Just (_, rep3,signed2) <- isIntConversion conv_outer
= case () of
-- widen then narrow to the same size is a nop
_ | rep1 < rep2 && rep1 == rep3 -> x
-- Widen then narrow to different size: collapse to single conversion
-- but remember to use the signedness from the widening, just in case
-- the final conversion is a widen.
| rep1 < rep2 && rep2 > rep3 ->
cmmMachOpFold (intconv signed1 rep1 rep3) [x]
-- Nested widenings: collapse if the signedness is the same
| rep1 < rep2 && rep2 < rep3 && signed1 == signed2 ->
cmmMachOpFold (intconv signed1 rep1 rep3) [x]
-- Nested narrowings: collapse
| rep1 > rep2 && rep2 > rep3 ->
cmmMachOpFold (MO_U_Conv rep1 rep3) [x]
| otherwise ->
CmmMachOp conv_outer args
where
isIntConversion (MO_U_Conv rep1 rep2)
| not (isFloatingRep rep1) && not (isFloatingRep rep2)
= Just (rep1,rep2,False)
isIntConversion (MO_S_Conv rep1 rep2)
| not (isFloatingRep rep1) && not (isFloatingRep rep2)
= Just (rep1,rep2,True)
isIntConversion _ = Nothing
intconv True = MO_S_Conv
intconv False = MO_U_Conv
-- ToDo: a narrow of a load can be collapsed into a narrow load, right?
-- but what if the architecture only supports word-sized loads, should
-- we do the transformation anyway?
cmmMachOpFold mop args@[CmmLit (CmmInt x xrep), CmmLit (CmmInt y _)]
= case mop of
-- for comparisons: don't forget to narrow the arguments before
-- comparing, since they might be out of range.
MO_Eq r -> CmmLit (CmmInt (if x_u == y_u then 1 else 0) wordRep)
MO_Ne r -> CmmLit (CmmInt (if x_u /= y_u then 1 else 0) wordRep)
MO_U_Gt r -> CmmLit (CmmInt (if x_u > y_u then 1 else 0) wordRep)
MO_U_Ge r -> CmmLit (CmmInt (if x_u >= y_u then 1 else 0) wordRep)
MO_U_Lt r -> CmmLit (CmmInt (if x_u < y_u then 1 else 0) wordRep)
MO_U_Le r -> CmmLit (CmmInt (if x_u <= y_u then 1 else 0) wordRep)
MO_S_Gt r -> CmmLit (CmmInt (if x_s > y_s then 1 else 0) wordRep)
MO_S_Ge r -> CmmLit (CmmInt (if x_s >= y_s then 1 else 0) wordRep)
MO_S_Lt r -> CmmLit (CmmInt (if x_s < y_s then 1 else 0) wordRep)
MO_S_Le r -> CmmLit (CmmInt (if x_s <= y_s then 1 else 0) wordRep)
MO_Add r -> CmmLit (CmmInt (x + y) r)
MO_Sub r -> CmmLit (CmmInt (x - y) r)
MO_Mul r -> CmmLit (CmmInt (x * y) r)
MO_S_Quot r | y /= 0 -> CmmLit (CmmInt (x `quot` y) r)
MO_S_Rem r | y /= 0 -> CmmLit (CmmInt (x `rem` y) r)
MO_And r -> CmmLit (CmmInt (x .&. y) r)
MO_Or r -> CmmLit (CmmInt (x .|. y) r)
MO_Xor r -> CmmLit (CmmInt (x `xor` y) r)
MO_Shl r -> CmmLit (CmmInt (x `shiftL` fromIntegral y) r)
MO_U_Shr r -> CmmLit (CmmInt (x_u `shiftR` fromIntegral y) r)
MO_S_Shr r -> CmmLit (CmmInt (x `shiftR` fromIntegral y) r)
other -> CmmMachOp mop args
where
x_u = narrowU xrep x
y_u = narrowU xrep y
x_s = narrowS xrep x
y_s = narrowS xrep y
-- When possible, shift the constants to the right-hand side, so that we
-- can match for strength reductions. Note that the code generator will
-- also assume that constants have been shifted to the right when
-- possible.
cmmMachOpFold op [x@(CmmLit _), y]
| not (isLit y) && isCommutableMachOp op
= cmmMachOpFold op [y, x]
-- Turn (a+b)+c into a+(b+c) where possible. Because literals are
-- moved to the right, it is more likely that we will find
-- opportunities for constant folding when the expression is
-- right-associated.
--
-- ToDo: this appears to introduce a quadratic behaviour due to the
-- nested cmmMachOpFold. Can we fix this?
--
-- Why do we check isLit arg1? If arg1 is a lit, it means that arg2
-- is also a lit (otherwise arg1 would be on the right). If we
-- put arg1 on the left of the rearranged expression, we'll get into a
-- loop: (x1+x2)+x3 => x1+(x2+x3) => (x2+x3)+x1 => x2+(x3+x1) ...
--
cmmMachOpFold mop1 [CmmMachOp mop2 [arg1,arg2], arg3]
| mop1 == mop2 && isAssociativeMachOp mop1 && not (isLit arg1)
= cmmMachOpFold mop1 [arg1, cmmMachOpFold mop2 [arg2,arg3]]
-- Make a RegOff if we can
cmmMachOpFold (MO_Add _) [CmmReg reg, CmmLit (CmmInt n rep)]
= CmmRegOff reg (fromIntegral (narrowS rep n))
cmmMachOpFold (MO_Add _) [CmmRegOff reg off, CmmLit (CmmInt n rep)]
= CmmRegOff reg (off + fromIntegral (narrowS rep n))
cmmMachOpFold (MO_Sub _) [CmmReg reg, CmmLit (CmmInt n rep)]
= CmmRegOff reg (- fromIntegral (narrowS rep n))
cmmMachOpFold (MO_Sub _) [CmmRegOff reg off, CmmLit (CmmInt n rep)]
= CmmRegOff reg (off - fromIntegral (narrowS rep n))
-- Fold label(+/-)offset into a CmmLit where possible
cmmMachOpFold (MO_Add _) [CmmLit (CmmLabel lbl), CmmLit (CmmInt i rep)]
= CmmLit (CmmLabelOff lbl (fromIntegral (narrowU rep i)))
cmmMachOpFold (MO_Add _) [CmmLit (CmmInt i rep), CmmLit (CmmLabel lbl)]
= CmmLit (CmmLabelOff lbl (fromIntegral (narrowU rep i)))
cmmMachOpFold (MO_Sub _) [CmmLit (CmmLabel lbl), CmmLit (CmmInt i rep)]
= CmmLit (CmmLabelOff lbl (fromIntegral (negate (narrowU rep i))))
-- We can often do something with constants of 0 and 1 ...
cmmMachOpFold mop args@[x, y@(CmmLit (CmmInt 0 _))]
= case mop of
MO_Add r -> x
MO_Sub r -> x
MO_Mul r -> y
MO_And r -> y
MO_Or r -> x
MO_Xor r -> x
MO_Shl r -> x
MO_S_Shr r -> x
MO_U_Shr r -> x
MO_Ne r | isComparisonExpr x -> x
MO_Eq r | Just x' <- maybeInvertConditionalExpr x -> x'
MO_U_Gt r | isComparisonExpr x -> x
MO_S_Gt r | isComparisonExpr x -> x
MO_U_Lt r | isComparisonExpr x -> CmmLit (CmmInt 0 wordRep)
MO_S_Lt r | isComparisonExpr x -> CmmLit (CmmInt 0 wordRep)
MO_U_Ge r | isComparisonExpr x -> CmmLit (CmmInt 1 wordRep)
MO_S_Ge r | isComparisonExpr x -> CmmLit (CmmInt 1 wordRep)
MO_U_Le r | Just x' <- maybeInvertConditionalExpr x -> x'
MO_S_Le r | Just x' <- maybeInvertConditionalExpr x -> x'
other -> CmmMachOp mop args
cmmMachOpFold mop args@[x, y@(CmmLit (CmmInt 1 rep))]
= case mop of
MO_Mul r -> x
MO_S_Quot r -> x
MO_U_Quot r -> x
MO_S_Rem r -> CmmLit (CmmInt 0 rep)
MO_U_Rem r -> CmmLit (CmmInt 0 rep)
MO_Ne r | Just x' <- maybeInvertConditionalExpr x -> x'
MO_Eq r | isComparisonExpr x -> x
MO_U_Lt r | Just x' <- maybeInvertConditionalExpr x -> x'
MO_S_Lt r | Just x' <- maybeInvertConditionalExpr x -> x'
MO_U_Gt r | isComparisonExpr x -> CmmLit (CmmInt 0 wordRep)
MO_S_Gt r | isComparisonExpr x -> CmmLit (CmmInt 0 wordRep)
MO_U_Le r | isComparisonExpr x -> CmmLit (CmmInt 1 wordRep)
MO_S_Le r | isComparisonExpr x -> CmmLit (CmmInt 1 wordRep)
MO_U_Ge r | isComparisonExpr x -> x
MO_S_Ge r | isComparisonExpr x -> x
other -> CmmMachOp mop args
-- Now look for multiplication/division by powers of 2 (integers).
cmmMachOpFold mop args@[x, y@(CmmLit (CmmInt n _))]
= case mop of
MO_Mul rep
-> case exactLog2 n of
Nothing -> unchanged
Just p -> CmmMachOp (MO_Shl rep) [x, CmmLit (CmmInt p rep)]
MO_S_Quot rep
-> case exactLog2 n of
Nothing -> unchanged
Just p -> CmmMachOp (MO_S_Shr rep) [x, CmmLit (CmmInt p rep)]
other
-> unchanged
where
unchanged = CmmMachOp mop args
-- Anything else is just too hard.
cmmMachOpFold mop args = CmmMachOp mop args
-- -----------------------------------------------------------------------------
-- exactLog2
-- This algorithm for determining the $\log_2$ of exact powers of 2 comes
-- from GCC. It requires bit manipulation primitives, and we use GHC
-- extensions. Tough.
--
-- Used to be in MachInstrs --SDM.
-- ToDo: remove use of unboxery --SDM.
w2i x = word2Int# x
i2w x = int2Word# x
exactLog2 :: Integer -> Maybe Integer
exactLog2 x
= if (x <= 0 || x >= 2147483648) then
Nothing
else
case iUnbox (fromInteger x) of { x# ->
if (w2i ((i2w x#) `and#` (i2w (0# -# x#))) /=# x#) then
Nothing
else
Just (toInteger (iBox (pow2 x#)))
}
where
pow2 x# | x# ==# 1# = 0#
| otherwise = 1# +# pow2 (w2i (i2w x# `shiftRL#` 1#))
-- -----------------------------------------------------------------------------
-- widening / narrowing
narrowU :: MachRep -> Integer -> Integer
narrowU I8 x = fromIntegral (fromIntegral x :: Word8)
narrowU I16 x = fromIntegral (fromIntegral x :: Word16)
narrowU I32 x = fromIntegral (fromIntegral x :: Word32)
narrowU I64 x = fromIntegral (fromIntegral x :: Word64)
narrowU _ _ = panic "narrowTo"
narrowS :: MachRep -> Integer -> Integer
narrowS I8 x = fromIntegral (fromIntegral x :: Int8)
narrowS I16 x = fromIntegral (fromIntegral x :: Int16)
narrowS I32 x = fromIntegral (fromIntegral x :: Int32)
narrowS I64 x = fromIntegral (fromIntegral x :: Int64)
narrowS _ _ = panic "narrowTo"
-- -----------------------------------------------------------------------------
-- The mini-inliner
-- This pass inlines assignments to temporaries that are used just
-- once in the very next statement only. Generalising this would be
-- quite difficult (have to take into account aliasing of memory
-- writes, and so on), but at the moment it catches a number of useful
-- cases and lets the code generator generate much better code.
-- NB. This assumes that temporaries are single-assignment.
cmmPeep :: [CmmBasicBlock] -> [CmmBasicBlock]
cmmPeep blocks = map do_inline blocks
where
blockUses (BasicBlock _ stmts)
= foldr (plusUFM_C (+)) emptyUFM (map getStmtUses stmts)
uses = foldr (plusUFM_C (+)) emptyUFM (map blockUses blocks)
do_inline (BasicBlock id stmts)
= BasicBlock id (cmmMiniInline uses stmts)
cmmMiniInline :: UniqFM Int -> [CmmStmt] -> [CmmStmt]
cmmMiniInline uses [] = []
cmmMiniInline uses (stmt@(CmmAssign (CmmLocal (LocalReg u _)) expr) : stmts)
| Just 1 <- lookupUFM uses u,
Just stmts' <- lookForInline u expr stmts
=
#ifdef NCG_DEBUG
trace ("nativeGen: inlining " ++ showSDoc (pprStmt stmt)) $
#endif
cmmMiniInline uses stmts'
cmmMiniInline uses (stmt:stmts)
= stmt : cmmMiniInline uses stmts
-- Try to inline a temporary assignment. We can skip over assignments to
-- other tempoararies, because we know that expressions aren't side-effecting
-- and temporaries are single-assignment.
lookForInline u expr (stmt@(CmmAssign (CmmLocal (LocalReg u' _)) rhs) : rest)
| u /= u'
= case lookupUFM (getExprUses rhs) u of
Just 1 -> Just (inlineStmt u expr stmt : rest)
_other -> case lookForInline u expr rest of
Nothing -> Nothing
Just stmts -> Just (stmt:stmts)
lookForInline u expr (CmmNop : rest)
= lookForInline u expr rest
lookForInline u expr (stmt:stmts)
= case lookupUFM (getStmtUses stmt) u of
Just 1 -> Just (inlineStmt u expr stmt : stmts)
_other -> Nothing
-- -----------------------------------------------------------------------------
-- Boring Cmm traversals for collecting usage info and substitutions.
getStmtUses :: CmmStmt -> UniqFM Int
getStmtUses (CmmAssign _ e) = getExprUses e
getStmtUses (CmmStore e1 e2) = plusUFM_C (+) (getExprUses e1) (getExprUses e2)
getStmtUses (CmmCall target _ es _)
= plusUFM_C (+) (uses target) (getExprsUses (map fst es))
where uses (CmmForeignCall e _) = getExprUses e
uses _ = emptyUFM
getStmtUses (CmmCondBranch e _) = getExprUses e
getStmtUses (CmmSwitch e _) = getExprUses e
getStmtUses (CmmJump e _) = getExprUses e
getStmtUses _ = emptyUFM
getExprUses :: CmmExpr -> UniqFM Int
getExprUses (CmmReg (CmmLocal (LocalReg u _))) = unitUFM u 1
getExprUses (CmmRegOff (CmmLocal (LocalReg u _)) _) = unitUFM u 1
getExprUses (CmmLoad e _) = getExprUses e
getExprUses (CmmMachOp _ es) = getExprsUses es
getExprUses _other = emptyUFM
getExprsUses es = foldr (plusUFM_C (+)) emptyUFM (map getExprUses es)
inlineStmt :: Unique -> CmmExpr -> CmmStmt -> CmmStmt
inlineStmt u a (CmmAssign r e) = CmmAssign r (inlineExpr u a e)
inlineStmt u a (CmmStore e1 e2) = CmmStore (inlineExpr u a e1) (inlineExpr u a e2)
inlineStmt u a (CmmCall target regs es vols)
= CmmCall (infn target) regs es' vols
where infn (CmmForeignCall fn cconv) = CmmForeignCall fn cconv
infn (CmmPrim p) = CmmPrim p
es' = [ (inlineExpr u a e, hint) | (e,hint) <- es ]
inlineStmt u a (CmmCondBranch e d) = CmmCondBranch (inlineExpr u a e) d
inlineStmt u a (CmmSwitch e d) = CmmSwitch (inlineExpr u a e) d
inlineStmt u a (CmmJump e d) = CmmJump (inlineExpr u a e) d
inlineStmt u a other_stmt = other_stmt
inlineExpr :: Unique -> CmmExpr -> CmmExpr -> CmmExpr
inlineExpr u a e@(CmmReg (CmmLocal (LocalReg u' _)))
| u == u' = a
| otherwise = e
inlineExpr u a e@(CmmRegOff (CmmLocal (LocalReg u' rep)) off)
| u == u' = CmmMachOp (MO_Add rep) [a, CmmLit (CmmInt (fromIntegral off) rep)]
| otherwise = e
inlineExpr u a (CmmLoad e rep) = CmmLoad (inlineExpr u a e) rep
inlineExpr u a (CmmMachOp op es) = CmmMachOp op (map (inlineExpr u a) es)
inlineExpr u a other_expr = other_expr
-- -----------------------------------------------------------------------------
-- Utils
bind f x = x $! f
isLit (CmmLit _) = True
isLit _ = False
isComparisonExpr :: CmmExpr -> Bool
isComparisonExpr (CmmMachOp op _) = isComparisonMachOp op
isComparisonExpr _other = False
maybeInvertConditionalExpr :: CmmExpr -> Maybe CmmExpr
maybeInvertConditionalExpr (CmmMachOp op args)
| Just op' <- maybeInvertComparison op = Just (CmmMachOp op' args)
maybeInvertConditionalExpr _ = Nothing
\end{code}
Markdown is supported
0% or .
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment