diff options
Diffstat (limited to 'compiler/GHC/Core/Opt/OccurAnal.hs')
| -rw-r--r-- | compiler/GHC/Core/Opt/OccurAnal.hs | 30 |
1 files changed, 27 insertions, 3 deletions
diff --git a/compiler/GHC/Core/Opt/OccurAnal.hs b/compiler/GHC/Core/Opt/OccurAnal.hs index 97d38c8bd1..a746e4feb8 100644 --- a/compiler/GHC/Core/Opt/OccurAnal.hs +++ b/compiler/GHC/Core/Opt/OccurAnal.hs @@ -1693,14 +1693,16 @@ occAnalUnfolding :: OccEnv occAnalUnfolding env is_rec mb_join_arity unf = case unf of unf@(CoreUnfolding { uf_tmpl = rhs, uf_src = src }) - | isStableSource src -> (usage, unf') - | otherwise -> (emptyDetails, unf) - where -- For non-Stable unfoldings we leave them undisturbed, but + | isStableSource src -> (markAllMany usage, unf') + -- markAllMany: see Note [Occurrences in stable unfoldings] + | otherwise -> (emptyDetails, unf) + -- For non-Stable unfoldings we leave them undisturbed, but -- don't count their usage because the simplifier will discard them. -- We leave them undisturbed because nodeScore uses their size info -- to guide its decisions. It's ok to leave un-substituted -- expressions in the tree because all the variables that were in -- scope remain in scope; there is no cloning etc. + where (usage, rhs') = occAnalRhs env is_rec mb_join_arity rhs unf' | noBinderSwaps env = unf -- Note [Unfoldings and rules] @@ -1759,6 +1761,28 @@ the FloatIn pass knows to float into join point RHSs; and the simplifier does not float things out of join point RHSs. But it's a simple, cheap thing to do. See #14137. +Note [Occurrences in stable unfoldings] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Consider + f p = BIG + {-# INLINE g #-} + g y = not (f y) +where this is the /only/ occurrence of 'f'. So 'g' will get a stable +unfolding. Now suppose that g's RHS gets optimised (perhaps by a rule +or inlining f) so that it doesn't mention 'f' any more. Now the last +remaining call to f is in g's Stable unfolding. But, even though there +is only one syntactic occurrence of f, we do /not/ want to do +preinlineUnconditionally here! + +The INLINE pragma says "inline exactly this RHS"; perhaps the +programmer wants to expose that 'not', say. If we inline f that will make +the Stable unfoldign big, and that wasn't what the programmer wanted. + +Another way to think about it: if we inlined g as-is into multiple +call sites, now there's be multiple calls to f. + +Bottom line: treat all occurrences in a stable unfolding as "Many". + Note [Unfoldings and rules] ~~~~~~~~~~~~~~~~~~~~~~~~~~~ Generally unfoldings and rules are already occurrence-analysed, so we |