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| author | Simon Peyton Jones <simonpj@microsoft.com> | 2013-06-25 11:56:59 +0100 |
|---|---|---|
| committer | Simon Peyton Jones <simonpj@microsoft.com> | 2013-06-25 11:58:01 +0100 |
| commit | 57284dbca501539e186e8587b6288e72c0488967 (patch) | |
| tree | 7cff148fa3a1526d11a7e9861dfda1d7dfe9165f | |
| parent | 316e8cba29ac25dccb054e9b73e2d174b7b4b61a (diff) | |
| download | haskell-57284dbca501539e186e8587b6288e72c0488967.tar.gz | |
Make noteMustPointToIt true of all non-top-level thunks
See Note [GC recovery]. To come: clean-up of StgCmmBind.cgRhs.
| -rw-r--r-- | compiler/codeGen/StgCmmClosure.hs | 67 |
1 files changed, 44 insertions, 23 deletions
diff --git a/compiler/codeGen/StgCmmClosure.hs b/compiler/codeGen/StgCmmClosure.hs index 04749e9da1..d5de7debd8 100644 --- a/compiler/codeGen/StgCmmClosure.hs +++ b/compiler/codeGen/StgCmmClosure.hs @@ -174,12 +174,12 @@ data LambdaFormInfo data StandardFormInfo = NonStandardThunk - -- Not of of the standard forms + -- The usual case: not of of the standard forms | SelectorThunk -- A SelectorThunk is of form -- case x of - -- con a1,..,an -> ak + -- con a1,..,an -> ak -- and the constructor is from a single-constr type. WordOff -- 0-origin offset of ak within the "goods" of -- constructor (Recall that the a1,...,an may be laid @@ -375,17 +375,33 @@ thunkClosureType _ = Thunk ----------------------------------------------------------------------------- nodeMustPointToIt :: DynFlags -> LambdaFormInfo -> Bool +-- If nodeMustPointToIt is true, then the entry convention for +-- this closure has R1 (the "Node" register) pointing to the +-- closure itself --- the "self" argument + nodeMustPointToIt _ (LFReEntrant top _ no_fvs _) - = not no_fvs || -- Certainly if it has fvs we need to point to it - isNotTopLevel top - -- If it is not top level we will point to it - -- We can have a \r closure with no_fvs which - -- is not top level as special case cgRhsClosure - -- has been dissabled in favour of let floating + = not no_fvs -- Certainly if it has fvs we need to point to it + || isNotTopLevel top -- See Note [GC recovery] + -- For lex_profiling we also access the cost centre for a + -- non-inherited (i.e. non-top-level) function. + -- The isNotTopLevel test above ensures this is ok. + +nodeMustPointToIt dflags (LFThunk top no_fvs updatable NonStandardThunk _) + = not no_fvs -- Self parameter + || isNotTopLevel top -- Note [GC recovery] + || updatable -- Need to push update frame + || gopt Opt_SccProfilingOn dflags + -- For the non-updatable (single-entry case): + -- + -- True if has fvs (in which case we need access to them, and we + -- should black-hole it) + -- or profiling (in which case we need to recover the cost centre + -- from inside it) ToDo: do we need this even for + -- top-level thunks? If not, + -- isNotTopLevel subsumes this - -- For lex_profiling we also access the cost centre for a - -- non-inherited function i.e. not top level - -- the not top case above ensures this is ok. +nodeMustPointToIt _ (LFThunk {}) -- Node must point to a standard-form thunk + = True nodeMustPointToIt _ (LFCon _) = True @@ -400,23 +416,28 @@ nodeMustPointToIt _ (LFCon _) = True -- having Node point to the result of an update. SLPJ -- 27/11/92. -nodeMustPointToIt dflags (LFThunk _ no_fvs updatable NonStandardThunk _) - = updatable || not no_fvs || gopt Opt_SccProfilingOn dflags - -- For the non-updatable (single-entry case): - -- - -- True if has fvs (in which case we need access to them, and we - -- should black-hole it) - -- or profiling (in which case we need to recover the cost centre - -- from inside it) - -nodeMustPointToIt _ (LFThunk {}) -- Node must point to a standard-form thunk - = True - nodeMustPointToIt _ (LFUnknown _) = True nodeMustPointToIt _ LFUnLifted = False nodeMustPointToIt _ LFBlackHole = True -- BH entry may require Node to point nodeMustPointToIt _ LFLetNoEscape = False +{- Note [GC recovery] +~~~~~~~~~~~~~~~~~~~~~ +If we a have a local let-binding (function or thunk) + let f = <body> in ... +AND <body> allocates, then the heap-overflow check needs to know how +to re-start the evaluation. It uses the "self" pointer to do this. +So even if there are no free variables in <body>, we still make +nodeMustPointToIt be True for non-top-level bindings. + +Why do any such bindings exist? After all, let-floating should have +floated them out. Well, a clever optimiser might leave one there to +avoid a space leak, deliberately recomputing a thunk. Also (and this +really does happen occasionally) let-floating may make a function f smaller +so it can be inlined, so now (f True) may generate a local no-fv closure. +This actually happened during bootsrapping GHC itself, with f=mkRdrFunBind +in TcGenDeriv.) -} + ----------------------------------------------------------------------------- -- getCallMethod ----------------------------------------------------------------------------- |