The only reason this is monadised is for the unique supply.
-Note [Don't w/w inline things (a)]
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
+Note [Don't w/w INLINE things]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
It's very important to refrain from w/w-ing an INLINE function (ie one
with an InlineRule) because the wrapper will then overwrite the
InlineRule unfolding.
in a recursive group. It might not be the loop breaker. (We could
test for loop-breaker-hood, but I'm not sure that ever matters.)
-Note [Don't w/w inline things (b)]
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-In general, we refrain from w/w-ing *small* functions, because they'll
-inline anyway. But we must take care: it may look small now, but get
-to be big later after other inling has happened. So we take the
-precaution of adding an INLINE pragma to any such functions.
+Note [Don't w/w INLINABLE things]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+If we have
+ {-# INLINABLE f #-}
+ f x y = ....
+then in principle we might get a more efficient loop by w/w'ing f.
+But that would make a new unfolding which would overwrite the old
+one. So we leave INLINABLE things alone too.
+
+This is a slight infelicity really, because it means that adding
+an INLINABLE pragma could make a program a bit less efficient,
+because you lose the worker/wrapper stuff. But I don't see a way
+to avoid that.
+
+Note [Don't w/w inline small non-loop-breaker things]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+In general, we refrain from w/w-ing *small* functions, which are not
+loop breakers, because they'll inline anyway. But we must take care:
+it may look small now, but get to be big later after other inlining
+has happened. So we take the precaution of adding an INLINE pragma to
+any such functions.
I made this change when I observed a big function at the end of
compilation with a useful strictness signature but no w-w. When
---------------------
checkSize :: Id -> CoreExpr
-> UniqSM [(Id,CoreExpr)] -> UniqSM [(Id,CoreExpr)]
- -- See Note [Don't w/w inline things (a) and (b)]
checkSize fn_id rhs thing_inside
- | isStableUnfolding unfolding -- For DFuns and INLINE things, leave their
- = return [ (fn_id, rhs) ] -- unfolding unchanged; but still attach
- -- strictness info to the Id
+ | isStableUnfolding (realIdUnfolding fn_id)
+ = return [ (fn_id, rhs) ]
+ -- See Note [Don't w/w INLINABLE things]
+ -- and Note [Don't w/w INLINABLABLE things]
+ -- NB: use realIdUnfolding because we want to see the unfolding
+ -- even if it's a loop breaker!
- | certainlyWillInline unfolding
+ | certainlyWillInline (idUnfolding fn_id)
= return [ (fn_id `setIdUnfolding` inline_rule, rhs) ]
- -- Note [Don't w/w inline things (b)]
+ -- Note [Don't w/w inline small non-loop-breaker things]
+ -- NB: use idUnfolding because we don't want to apply
+ -- this criterion to a loop breaker!
| otherwise = thing_inside
where
- unfolding = idUnfolding fn_id
inline_rule = mkInlineUnfolding Nothing rhs
---------------------