[project @ 2002-02-14 15:08:08 by simonpj]

-------------------------------------------------
	Undo an earlier hack in postInlineUnconditionally
	-------------------------------------------------

In an earlier era I made postInlineUnconditionally rather less
aggressive; it didn't inline even trivial things unless they
occurred just once.  THis was a hack designed to avoid rules
unexpectedly not firing.  But now we have much more control
over rules, through the phase numbering stuff, so I can undo the
hack.

Well, so I believe.  Manuel, yell if your rules stop working!

diff --git a/ghc/compiler/simplCore/SimplMonad.lhs b/ghc/compiler/simplCore/SimplMonad.lhs
index d3f10a0..266d9ec 100644 (file)
--- a/ghc/compiler/simplCore/SimplMonad.lhs
+++ b/ghc/compiler/simplCore/SimplMonad.lhs
@@ -71,7 +71,7 @@ import UniqSupply     ( uniqsFromSupply, uniqFromSupply, splitUniqSupply,
                          UniqSupply
                        )
 import FiniteMap
-import BasicTypes      ( TopLevelFlag, isTopLevel, 
+import BasicTypes      ( TopLevelFlag, isTopLevel, isLoopBreaker,
                          Activation, isActive, isAlwaysActive,
                          OccInfo(..), isOneOcc
                        )
@@ -862,16 +862,27 @@ story for now.
 \begin{code}
 postInlineUnconditionally :: SimplEnv -> OutId -> OccInfo -> OutExpr -> Bool
 postInlineUnconditionally env bndr occ_info rhs 
-  =  exprIsTrivial rhs && active && isOneOcc occ_info
-       -- We used to have (not loop_breaker && not (isExportedId bndr))
-       -- instead of (isOneOcc occ_info).  Indeed, you might suppose that
+  =  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 (e.g. PrelEnum.eftInt).
+       -- This is important in the rules for the Prelude 
   where
     active = case getMode env of
                   SimplGently  -> isAlwaysActive prag