etaExpand, exprEtaExpandArity, bindNonRec, mkCoerce2,
findDefault, exprOkForSpeculation, exprIsValue
)
-import Id ( idType, isDataConWorkId, idOccInfo, isDictId,
+import Id ( idType, isDataConWorkId, idOccInfo, isDictId, idArity,
mkSysLocal, isDeadBinder, idNewDemandInfo, isExportedId,
idUnfolding, idNewStrictness, idInlinePragma,
)
import DataCon ( dataConRepArity, dataConTyVars, dataConArgTys, isVanillaDataCon )
import Var ( tyVarKind, mkTyVar )
import VarSet
-import BasicTypes ( TopLevelFlag(..), isTopLevel, OccInfo(..), isLoopBreaker, isOneOcc,
+import BasicTypes ( TopLevelFlag(..), isTopLevel, isNotTopLevel, OccInfo(..), isLoopBreaker, isOneOcc,
Activation, isAlwaysActive, isActive )
import Util ( lengthExceeds )
import Outputable
xN = eN[xN-1]
We may end up simplifying e1 N times, e2 N-1 times, e3 N-3 times etc.
+This can happen with cascades of functions too:
+
+ f1 = \x1.e1
+ f2 = \xs.e2[f1]
+ f3 = \xs.e3[f3]
+ ...etc...
+
+THE MAIN INVARIANT is this:
+
+ ---- preInlineUnconditionally invariant -----
+ IF preInlineUnconditionally chooses to inline x = <rhs>
+ THEN doing the inlining should not change the occurrence
+ info for the free vars of <rhs>
+ ----------------------------------------------
+
+For example, it's tempting to look at trivial binding like
+ x = y
+and inline it unconditionally. But suppose x is used many times,
+but this is the unique occurrence of y. Then inlining x would change
+y's occurrence info, which breaks the invariant. It matters: y
+might have a BIG rhs, which will now be dup'd at every occurrenc of x.
-NB: we don't even look at the RHS to see if it's trivial
-We might have
- x = y
-where x is used many times, but this is the unique occurrence of y.
-We should NOT inline x at all its uses, because then we'd do the same
-for y -- aargh! So we must base this pre-rhs-simplification decision
-solely on x's occurrences, not on its rhs.
Evne RHSs labelled InlineMe aren't caught here, because there might be
no benefit from inlining at the call site.
phase), at which point don't.
\begin{code}
-preInlineUnconditionally :: SimplEnv -> TopLevelFlag -> InId -> Bool
-preInlineUnconditionally env top_lvl bndr
- | isTopLevel top_lvl, SimplPhase 0 <- phase = False
--- If we don't have this test, consider
+preInlineUnconditionally :: SimplEnv -> TopLevelFlag -> InId -> InExpr -> Bool
+preInlineUnconditionally env top_lvl bndr rhs
+ | not active = False
+ | opt_SimplNoPreInlining = False
+ | otherwise = case idOccInfo bndr of
+ IAmDead -> True -- Happens in ((\x.1) v)
+ OneOcc in_lam True int_cxt -> try_once in_lam int_cxt
+ other -> False
+ where
+ phase = getMode env
+ active = case phase of
+ SimplGently -> isAlwaysActive prag
+ SimplPhase n -> isActive n prag
+ prag = idInlinePragma bndr
+
+ try_once in_lam int_cxt -- There's one textual occurrence
+ = not in_lam && (isNotTopLevel top_lvl || early_phase)
+ || (exprIsValue rhs && int_cxt)
+ -- exprIsValue => free vars of rhs are (Once in_lam) or Many,
+ -- so substituting rhs inside a lambda doesn't change the occ info
+ -- Caveat: except the fn of a PAP, but since it has arity > 0, it
+ -- must be a HNF, so it doesn't matter if we push it inside
+ -- a lambda
+ --
+ -- int_cxt The context isn't totally boring
+ -- E.g. let f = \ab.BIG in \y. map f xs
+ -- Don't want to substitute for f, because then we allocate
+ -- its closure every time the \y is called
+ -- But: let f = \ab.BIG in \y. map (f y) xs
+ -- Now we do want to substitute for f, even though it's not
+ -- saturated, because we're going to allocate a closure for
+ -- (f y) every time round the loop anyhow.
+
+ early_phase = case phase of
+ SimplPhase 0 -> False
+ other -> True
+-- If we don't have this early_phase test, consider
-- x = length [1,2,3]
-- The full laziness pass carefully floats all the cons cells to
-- top level, and preInlineUnconditionally floats them all back in.
-- top level things, but then we become more leery about inlining
-- them.
- | not active = False
- | opt_SimplNoPreInlining = False
- | otherwise = case idOccInfo bndr of
- IAmDead -> True -- Happens in ((\x.1) v)
- OneOcc in_lam once -> not in_lam && once
- -- Not inside a lambda, one occurrence ==> safe!
- other -> False
- where
- phase = getMode env
- active = case phase of
- SimplGently -> isAlwaysActive prag
- SimplPhase n -> isActive n prag
- prag = idInlinePragma bndr
\end{code}
postInlineUnconditionally
\begin{code}
postInlineUnconditionally :: SimplEnv -> OutId -> OccInfo -> OutExpr -> Bool
-postInlineUnconditionally env bndr occ_info rhs
- = exprIsTrivial rhs
- && active
- && not (isLoopBreaker occ_info)
- && not (isExportedId bndr)
- -- We used to have (isOneOcc occ_info) instead of
- -- not (isLoopBreaker occ_info) && not (isExportedId bndr)
- -- That was because a rather fragile use of rules got confused
- -- if you inlined even a binding f=g e.g. We used to have
- -- map = mapList
- -- But now a more precise use of phases has eliminated this problem,
- -- so the is_active test will do the job. I think.
- --
- -- OLD COMMENT: (delete soon)
- -- Indeed, you might suppose that
- -- there is nothing wrong with substituting for a trivial RHS, even
- -- if it occurs many times. But consider
- -- x = y
- -- h = _inline_me_ (...x...)
- -- Here we do *not* want to have x inlined, even though the RHS is
- -- trivial, becuase the contract for an INLINE pragma is "no inlining".
- -- This is important in the rules for the Prelude
+postInlineUnconditionally env bndr occ_info rhs
+ | not active = False
+ | isLoopBreaker occ_info = False
+ | isExportedId bndr = False
+ | exprIsTrivial rhs = True
+ | otherwise = False
where
active = case getMode env of
SimplGently -> isAlwaysActive prag
projects / ghc-hetmet.git / blobdiff