%* *
%************************************************************************
-\begin{code}
-simplEnvForGHCi :: SimplEnv
-simplEnvForGHCi = mkSimplEnv allOffSwitchChecker $
- SimplGently { sm_rules = False, sm_inline = False }
- -- Do not do any inlining, in case we expose some unboxed
- -- tuple stuff that confuses the bytecode interpreter
-
-simplEnvForRules :: SimplEnv
-simplEnvForRules = mkSimplEnv allOffSwitchChecker $
- SimplGently { sm_rules = True, sm_inline = False }
-
-updModeForInlineRules :: SimplifierMode -> SimplifierMode
-updModeForInlineRules mode
- = case mode of
- SimplGently {} -> mode -- Don't modify mode if we already gentle
- SimplPhase {} -> SimplGently { sm_rules = True, sm_inline = True }
- -- Simplify as much as possible, subject to the usual "gentle" rules
-\end{code}
-
Inlining is controlled partly by the SimplifierMode switch. This has two
settings
to work in Template Haskell when simplifying
splices, so we get simpler code for literal strings
-Note [Simplifying gently inside InlineRules]
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-We don't do much simplification inside InlineRules (which come from
-INLINE pragmas). It really is important to switch off inlinings
-inside such expressions. Consider the following example
+Note [Simplifying inside InlineRules]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+We must take care with simplification inside InlineRules (which come from
+INLINE pragmas).
+First, consider the following example
let f = \pq -> BIG
in
let g = \y -> f y y
{-# INLINE g #-}
in ...g...g...g...g...g...
+Now, if that's the ONLY occurrence of f, it might be inlined inside g,
+and thence copied multiple times when g is inlined. HENCE we treat
+any occurrence in an InlineRule as a multiple occurrence, not a single
+one; see OccurAnal.addRuleUsage.
+
+Second, we do want *do* to some modest rules/inlining stuff in InlineRules,
+partly to eliminate senseless crap, and partly to break the recursive knots
+generated by instance declarations. To keep things simple, we always set
+the phase to 'gentle' when processing InlineRules. OK, so suppose we have
+ {-# INLINE <act> f #-}
+ f = <rhs>
+meaning "inline f in phases p where activation <act>(p) holds".
+Then what inlinings/rules can we apply to the copy of <rhs> captured in
+f's InlineRule? Our model is that literally <rhs> is substituted for
+f when it is inlined. So our conservative plan (implemented by
+updModeForInlineRules) is this:
+
+ -------------------------------------------------------------
+ When simplifying the RHS of an InlineRule,
+ If the InlineRule becomes active in phase p, then
+ if the current phase is *earlier than* p,
+ make no inlinings or rules active when simplifying the RHS
+ otherwise
+ set the phase to p when simplifying the RHS
+ -------------------------------------------------------------
+
+That ensures that
+
+ a) Rules/inlinings that *cease* being active before p will
+ not apply to the InlineRule rhs, consistent with it being
+ inlined in its *original* form in phase p.
+
+ b) Rules/inlinings that only become active *after* p will
+ not apply to the InlineRule rhs, again to be consistent with
+ inlining the *original* rhs in phase p.
+
+For example,
+ {-# INLINE f #-}
+ f x = ...g...
-Now, if that's the ONLY occurrence of f, it will be inlined inside g,
-and thence copied multiple times when g is inlined.
+ {-# NOINLINE [1] g #-}
+ g y = ...
-This function may be inlinined in other modules, so we don't want to
-remove (by inlining) calls to functions that have specialisations, or
-that may have transformation rules in an importing scope.
+ {-# RULE h g = ... #-}
+Here we must not inline g into f's RHS, even when we get to phase 0,
+because when f is later inlined into some other module we want the
+rule for h to fire.
-E.g. {-# INLINE f #-}
+Similarly, consider
+ {-# INLINE f #-}
f x = ...g...
-and suppose that g is strict *and* has specialisations. If we inline
-g's wrapper, we deny f the chance of getting the specialised version
-of g when f is inlined at some call site (perhaps in some other
-module).
+ g y = ...
+and suppose that there are auto-generated specialisations and a strictness
+wrapper for g. The specialisations get activation AlwaysActive, and the
+strictness wrapper get activation (ActiveAfter 0). So the strictness
+wrepper fails the test and won't be inlined into f's InlineRule. That
+means f can inline, expose the specialised call to g, so the specialisation
+rules can fire.
+A note about wrappers
+~~~~~~~~~~~~~~~~~~~~~
It's also important not to inline a worker back into a wrapper.
A wrapper looks like
wraper = inline_me (\x -> ...worker... )
the wrapper (initially, the worker's only call site!). But,
if the wrapper is sure to be called, the strictness analyser will
mark it 'demanded', so when the RHS is simplified, it'll get an ArgOf
-continuation. That's why the keep_inline predicate returns True for
-ArgOf continuations. It shouldn't do any harm not to dissolve the
-inline-me note under these circumstances.
+continuation.
-Although we do very little simplification inside an InlineRule,
-the RHS is simplified as normal. For example:
+\begin{code}
+simplEnvForGHCi :: SimplEnv
+simplEnvForGHCi = mkSimplEnv allOffSwitchChecker $
+ SimplGently { sm_rules = False, sm_inline = False }
+ -- Do not do any inlining, in case we expose some unboxed
+ -- tuple stuff that confuses the bytecode interpreter
- all xs = foldr (&&) True xs
- any p = all . map p {-# INLINE any #-}
+simplEnvForRules :: SimplEnv
+simplEnvForRules = mkSimplEnv allOffSwitchChecker $
+ SimplGently { sm_rules = True, sm_inline = False }
+
+updModeForInlineRules :: Activation -> SimplifierMode -> SimplifierMode
+-- See Note [Simplifying inside InlineRules]
+-- Treat Gentle as phase "infinity"
+-- If current_phase `earlier than` inline_rule_start_phase
+-- then no_op
+-- else
+-- if current_phase `same phase` inline_rule_start_phase
+-- then current_phase (keep gentle flags)
+-- else inline_rule_start_phase
+updModeForInlineRules inline_rule_act current_mode
+ = case inline_rule_act of
+ NeverActive -> no_op
+ AlwaysActive -> mk_gentle current_mode
+ ActiveBefore {} -> mk_gentle current_mode
+ ActiveAfter n -> mk_phase n current_mode
+ where
+ no_op = SimplGently { sm_rules = False, sm_inline = False }
+
+ mk_gentle (SimplGently {}) = current_mode
+ mk_gentle _ = SimplGently { sm_rules = True, sm_inline = True }
-The RHS of 'any' will get optimised and deforested; but the InlineRule
-will still mention the original RHS.
+ mk_phase n (SimplPhase cp ss)
+ | cp > n = no_op -- Current phase earlier than n
+ | otherwise = SimplPhase n ss
+ mk_phase _ (SimplGently {}) = no_op
+\end{code}
preInlineUnconditionally
projects / ghc-hetmet.git / blobdiff