X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2Fprelude%2FPrimOp.lhs;h=4ac157770703a7ca08057df2fa92ee06c4cda561;hp=c2cac8f3d8fc464e26a07e3b44c5f994dcc7e184;hb=2662dbc5b2c30fc11ccb99e7f9b2dba794d680ba;hpb=d7b3ad9be373e02ea8b679d978f6ca898436892d

diff --git a/compiler/prelude/PrimOp.lhs b/compiler/prelude/PrimOp.lhs
index c2cac8f..4ac1577 100644
--- a/compiler/prelude/PrimOp.lhs
+++ b/compiler/prelude/PrimOp.lhs
@@ -4,7 +4,6 @@
 \section[PrimOp]{Primitive operations (machine-level)}
 
 \begin{code}
-{-# OPTIONS_GHC -H80m #-}
 {-# OPTIONS -fno-warn-unused-binds #-}
 -- The above warning supression flag is a temporary kludge.
 -- While working on this module you are encouraged to remove it and fix
@@ -22,7 +21,9 @@ module PrimOp (
 	primOpOutOfLine, primOpNeedsWrapper, 
 	primOpOkForSpeculation, primOpIsCheap, primOpIsDupable,
 
-	getPrimOpResultInfo,  PrimOpResultInfo(..)
+	getPrimOpResultInfo,  PrimOpResultInfo(..),
+
+        PrimCall(..)
     ) where
 
 #include "HsVersions.h"
@@ -30,13 +31,14 @@ module PrimOp (
 import TysPrim
 import TysWiredIn
 
-import NewDemand
+import Demand
 import Var		( TyVar )
 import OccName		( OccName, pprOccName, mkVarOccFS )
 import TyCon		( TyCon, isPrimTyCon, tyConPrimRep, PrimRep(..) )
 import Type		( Type, mkForAllTys, mkFunTy, mkFunTys, tyConAppTyCon,
 			  typePrimRep )
 import BasicTypes	( Arity, Boxity(..) )
+import ForeignCall	( CLabelString )
 import Unique		( Unique, mkPrimOpIdUnique )
 import Outputable
 import FastTypes
@@ -381,6 +383,38 @@ primOpCanFail :: PrimOp -> Bool
 And some primops have side-effects and so, for example, must not be
 duplicated.
 
+This predicate means a little more than just "modifies the state of
+the world".  What it really means is "it cosumes the state on its
+input".  To see what this means, consider
+
+ let
+     t = case readMutVar# v s0 of (# s1, x #) -> (S# s1, x)
+     y = case t of (s,x) -> x
+ in
+     ... y ... y ...
+
+Now, this is part of an ST or IO thread, so we are guaranteed by
+construction that the program uses the state in a single-threaded way.
+Whenever the state resulting from the readMutVar# is demanded, the
+readMutVar# will be performed, and it will be ordered correctly with
+respect to other operations in the monad.
+
+But there's another way this could go wrong: GHC can inline t into y,
+and inline y.  Then although the original readMutVar# will still be
+correctly ordered with respect to the other operations, there will be
+one or more extra readMutVar#s performed later, possibly out-of-order.
+This really happened; see #3207.
+
+The property we need to capture about readMutVar# is that it consumes
+the State# value on its input.  We must retain the linearity of the
+State#.
+
+Our fix for this is to declare any primop that must be used linearly
+as having side-effects.  When primOpHasSideEffects is True,
+primOpOkForSpeculation will be False, and hence primOpIsCheap will
+also be False, and applications of the primop will never be
+duplicated.
+
 \begin{code}
 primOpHasSideEffects :: PrimOp -> Bool
 #include "primop-has-side-effects.hs-incl"
@@ -475,3 +509,17 @@ pprPrimOp  :: PrimOp -> SDoc
 pprPrimOp other_op = pprOccName (primOpOcc other_op)
 \end{code}
 
+
+%************************************************************************
+%*									*
+\subsubsection[PrimCall]{User-imported primitive calls}
+%*									*
+%************************************************************************
+
+\begin{code}
+newtype PrimCall = PrimCall CLabelString
+
+instance Outputable PrimCall where
+  ppr (PrimCall lbl) = ppr lbl
+
+\end{code}