diff options
Diffstat (limited to 'compiler/cmm/SMRep.hs')
| -rw-r--r-- | compiler/cmm/SMRep.hs | 54 |
1 files changed, 41 insertions, 13 deletions
diff --git a/compiler/cmm/SMRep.hs b/compiler/cmm/SMRep.hs index ecd8905cbb..83ddf18586 100644 --- a/compiler/cmm/SMRep.hs +++ b/compiler/cmm/SMRep.hs @@ -177,6 +177,7 @@ data SMRep -- | True <=> This is a static closure. Affects how we garbage-collect it. -- Static closure have an extra static link field at the end. +-- Constructors do not have a static variant; see Note [static constructors] type IsStatic = Bool -- From an SMRep you can get to the closure type defined in @@ -287,10 +288,10 @@ isFunRep (HeapRep _ _ _ Fun{}) = True isFunRep _ = False isStaticNoCafCon :: SMRep -> Bool --- This should line up exactly with CONSTR_NOCAF_STATIC above +-- This should line up exactly with CONSTR_NOCAF below -- See Note [Static NoCaf constructors] -isStaticNoCafCon (HeapRep True 0 _ Constr{}) = True -isStaticNoCafCon _ = False +isStaticNoCafCon (HeapRep _ 0 _ Constr{}) = True +isStaticNoCafCon _ = False ----------------------------------------------------------------------------- @@ -428,12 +429,15 @@ rtsClosureType rep = case rep of RTSRep ty _ -> ty - HeapRep False 1 0 Constr{} -> CONSTR_1_0 - HeapRep False 0 1 Constr{} -> CONSTR_0_1 - HeapRep False 2 0 Constr{} -> CONSTR_2_0 - HeapRep False 1 1 Constr{} -> CONSTR_1_1 - HeapRep False 0 2 Constr{} -> CONSTR_0_2 - HeapRep False _ _ Constr{} -> CONSTR + -- See Note [static constructors] + HeapRep _ 1 0 Constr{} -> CONSTR_1_0 + HeapRep _ 0 1 Constr{} -> CONSTR_0_1 + HeapRep _ 2 0 Constr{} -> CONSTR_2_0 + HeapRep _ 1 1 Constr{} -> CONSTR_1_1 + HeapRep _ 0 2 Constr{} -> CONSTR_0_2 + HeapRep _ 0 _ Constr{} -> CONSTR_NOCAF + -- See Note [Static NoCaf constructors] + HeapRep _ _ _ Constr{} -> CONSTR HeapRep False 1 0 Fun{} -> FUN_1_0 HeapRep False 0 1 Fun{} -> FUN_0_1 @@ -451,10 +455,6 @@ rtsClosureType rep HeapRep False _ _ ThunkSelector{} -> THUNK_SELECTOR - -- Approximation: we use the CONSTR_NOCAF_STATIC type for static - -- constructors -- that have no pointer words only. - HeapRep True 0 _ Constr{} -> CONSTR_NOCAF_STATIC -- See isStaticNoCafCon below - HeapRep True _ _ Constr{} -> CONSTR_STATIC HeapRep True _ _ Fun{} -> FUN_STATIC HeapRep True _ _ Thunk{} -> THUNK_STATIC @@ -472,6 +472,34 @@ aRG_GEN = ARG_GEN aRG_GEN_BIG = ARG_GEN_BIG {- +Note [static constructors] +~~~~~~~~~~~~~~~~~~~~~~~~~~ + +We used to have a CONSTR_STATIC closure type, and each constructor had +two info tables: one with CONSTR (or CONSTR_1_0 etc.), and one with +CONSTR_STATIC. + +This distinction was removed, because when copying a data structure +into a compact region, we must copy static constructors into the +compact region too. If we didn't do this, we would need to track the +references from the compact region out to the static constructors, +because they might (indirectly) refer to CAFs. + +Since static constructors will be copied to the heap, if we wanted to +use different info tables for static and dynamic constructors, we +would have to switch the info pointer when copying the constructor +into the compact region, which means we would need an extra field of +the static info table to point to the dynamic one. + +However, since the distinction between static and dynamic closure +types is never actually needed (other than for assertions), we can +just drop the distinction and use the same info table for both. + +The GC *does* need to distinguish between static and dynamic closures, +but it does this using the HEAP_ALLOCED() macro which checks whether +the address of the closure resides within the dynamic heap. +HEAP_ALLOCED() doesn't read the closure's info table. + Note [Static NoCaf constructors] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ If we know that a top-level binding 'x' is not Caffy (ie no CAFs are |