Commit ac049528 authored by simonpj's avatar simonpj
Browse files

[project @ 1999-08-24 08:52:25 by simonpj]

Make primOpHasSideEffects return True for the various Write primops.
Amazingly, this wasn't done, and that meant that Write operations
could be silently discarded!  This broke the GHC typechecker
(actually the implementation of checkNoErrsTc, showed up in
deriving code)
parent 08dab195
......@@ -1967,36 +1967,56 @@ primOpOutOfLine op
_ -> False
\end{code}
primOpOkForSpeculation
~~~~~~~~~~~~~~~~~~~~~~
Sometimes we may choose to execute a PrimOp even though it isn't
certain that its result will be required; ie execute them
``speculatively''. The same thing as ``cheap eagerness.'' Usually
this is OK, because PrimOps are usually cheap, but it isn't OK for
(a)~expensive PrimOps and (b)~PrimOps which can fail.
PrimOps that have side effects also should not be executed speculatively.
Ok-for-speculation also means that it's ok *not* to execute the
primop. For example
case op a b of
r -> 3
Here the result is not used, so we can discard the primop. Anything
that has side effects mustn't be dicarded in this way, of course!
See also @primOpIsCheap@ (below).
PrimOps that have side effects also should not be executed speculatively
or by data dependencies.
\begin{code}
primOpOkForSpeculation :: PrimOp -> Bool
-- See comments with CoreUtils.exprOkForSpeculation
primOpOkForSpeculation op
= not (primOpCanFail op || primOpHasSideEffects op || primOpOutOfLine op)
\end{code}
primOpIsCheap
~~~~~~~~~~~~~
@primOpIsCheap@, as used in \tr{SimplUtils.lhs}. For now (HACK
WARNING), we just borrow some other predicates for a
what-should-be-good-enough test. "Cheap" means willing to call it more
than once. Evaluation order is unaffected.
\begin{code}
primOpIsCheap :: PrimOp -> Bool
-- See comments with CoreUtils.exprOkForSpeculation
primOpIsCheap op = not (primOpHasSideEffects op || primOpOutOfLine op)
\end{code}
primOpIsDupable
~~~~~~~~~~~~~~~
primOpIsDupable means that the use of the primop is small enough to
duplicate into different case branches. See CoreUtils.exprIsDupable.
\begin{code}
primOpIsDupable :: PrimOp -> Bool
-- See comments with CoreUtils.exprIsDupable
primOpIsDupable (CCallOp _ _ might_gc _) = not might_gc
-- If the ccall can't GC then the call is pretty cheap, and
-- we're happy to duplicate
......@@ -2035,11 +2055,6 @@ duplicated.
\begin{code}
primOpHasSideEffects :: PrimOp -> Bool
primOpHasSideEffects TakeMVarOp = True
primOpHasSideEffects DelayOp = True
primOpHasSideEffects WaitReadOp = True
primOpHasSideEffects WaitWriteOp = True
primOpHasSideEffects ParOp = True
primOpHasSideEffects ForkOp = True
primOpHasSideEffects KillThreadOp = True
......@@ -2056,6 +2071,27 @@ primOpHasSideEffects MakeStableNameOp = True
primOpHasSideEffects EqStablePtrOp = True -- SOF
primOpHasSideEffects DeRefStablePtrOp = True -- ??? JSM & ADR
-- In general, writes are considered a side effect, but
-- reads and variable allocations are not
-- Why? Because writes must not be omitted, but reads can be if their result is not used.
-- (Sequencing of reads is maintained by data dependencies on the resulting
-- world state.)
primOpHasSideEffects WriteArrayOp = True
primOpHasSideEffects (WriteByteArrayOp _) = True
primOpHasSideEffects (WriteOffAddrOp _) = True
primOpHasSideEffects WriteMutVarOp = True
primOpHasSideEffects UnsafeFreezeArrayOp = True
primOpHasSideEffects UnsafeFreezeByteArrayOp = True
primOpHasSideEffects UnsafeThawArrayOp = True
primOpHasSideEffects UnsafeThawByteArrayOp = True
primOpHasSideEffects TakeMVarOp = True
primOpHasSideEffects PutMVarOp = True
primOpHasSideEffects DelayOp = True
primOpHasSideEffects WaitReadOp = True
primOpHasSideEffects WaitWriteOp = True
primOpHasSideEffects ParGlobalOp = True
primOpHasSideEffects ParLocalOp = True
primOpHasSideEffects ParAtOp = True
......
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