Re: StgRhsClosure freevar and argument name duplicates

An example for the duplication please check the divModInteger https://github.com/ghc/ghc/blob/master/libraries/integer-simple/GHC/Integer/... function from integer-simple GHC.Integer.Type. The STG (GHC 8.2.2) generated from *divModInteger **:: Integer -> Integer -> (# Integer, Integer #) *contains duplications in a closure binder list. Using my custom STG printer it looks like: module GHC.Integer.Type where using GHC.Prim using GHC.Tuple using GHC.Types GHC.Integer.Type.divModInteger {-083-} = closure (F:) (B: n.s84123 {-s84123-} d.s84124 {-s84124-}) { case GHC.Integer.Type.quotRemInteger {-084-} n.s84123 {-s84123-} d.s84124 {-s84124-} of qr.s84125 {-s84125-} { GHC.Prim.(#,#) {-86-} ipv.s84126 {-s84126-} ipv1.s84127 {-s84127-} -> let $j.s84128 {-s84128-} = closure (F: d.s84124 {-s84124-} * ipv.s84126 {-s84126-}* * ipv1.s84127 {-s84127-}* * ipv.s84126 {-s84126-}* *ipv1.s84127 {-s84127-}*) (B: wild.s84129 {-s84129-}) { let $j1.s84130 {-s84130-} = closure (F: d.s84124 {-s84124-} ipv.s84126 {-s84126-} ipv1.s84127 {-s84127-} ipv.s84126 {-s84126-} ipv1.s84127 {-s84127-} wild.s84129 {-s84129-}) (B: wild1.s84131 {-s84131-}) { case _stg_prim_negateInt# wild.s84129 {-s84129-} of sat.s84132 {-s84132-} { DEFAULT -> case _stg_prim_==# wild1.s84131 {-s84131-} sat.s84132 {-s84132-} of sat.s84133 {-s84133-} { DEFAULT -> case _stg_prim_tagToEnum# sat.s84133 {-s84133-} of wild2.s84134 {-s84134-} { GHC.Types.False {-612-} -> GHC.Prim.(#,#) {-86-} ipv.s84126 {-s84126-} ipv1.s84127 {-s84127-} GHC.Types.True {-645-} -> case GHC.Integer.Type.plusInteger {-066-} ipv1.s84127 {-s84127-} d.s84124 {-s84124-} of r'.s84135 {-s84135-} { DEFAULT -> case GHC.Integer.Type.plusInteger {-066-} ipv.s84126 {-s84126-} GHC.Integer.Type.lvl11 {-r50574-} of q'.s84136 {-s84136-} { DEFAULT -> GHC.Prim.(#,#) {-86-} q'.s84136 {-s84136-} r'.s84135 {-s84135-} } } } } }} in case ipv1.s84127 {-s84127-} of wild1.s84137 {-s84137-} { GHC.Integer.Type.S# {-621-} i#.s84138 {-s84138-} -> case _stg_prim_<# i#.s84138 {-s84138-} 0# of sat.s84140 {-s84140-} { DEFAULT -> case _stg_prim_># i#.s84138 {-s84138-} 0# of sat.s84139 {-s84139-} { DEFAULT -> case _stg_prim_-# sat.s84139 {-s84139-} sat.s84140 {-s84140-} of sat.s84141 {-s84141-} { DEFAULT -> $j1.s84130 {-s84130-} sat.s84141 {-s84141-} } } } GHC.Integer.Type.Jp# {-r5813-} dt.s84142 {-s84142-} -> $j1.s84130 {-s84130-} 1# GHC.Integer.Type.Jn# {-r5814-} dt.s84143 {-s84143-} -> $j1.s84130 {-s84130-} -1# }} in case d.s84124 {-s84124-} of wild.s84144 {-s84144-} { GHC.Integer.Type.S# {-621-} i#.s84145 {-s84145-} -> case _stg_prim_<# i#.s84145 {-s84145-} 0# of sat.s84147 {-s84147-} { DEFAULT -> case _stg_prim_># i#.s84145 {-s84145-} 0# of sat.s84146 {-s84146-} { DEFAULT -> case _stg_prim_-# sat.s84146 {-s84146-} sat.s84147 {-s84147-} of sat.s84148 {-s84148-} { DEFAULT -> $j.s84128 {-s84128-} sat.s84148 {-s84148-} } } } GHC.Integer.Type.Jp# {-r5813-} dt.s84149 {-s84149-} -> $j.s84128 {-s84128-} 1# GHC.Integer.Type.Jn# {-r5814-} dt.s84150 {-s84150-} -> $j.s84128 {-s84128-} -1# } }} On Mon, Nov 5, 2018 at 2:08 PM Simon Peyton Jones wrote:

I don’t think there should be duplicates in either. Do you have a test case that shows duplicates?

Simon

*From:* ghc-devs *On Behalf Of *Csaba Hruska *Sent:* 04 November 2018 11:22 *To:* ghc-devs@haskell.org *Subject:* Re: StgRhsClosure freevar and argument name duplicates

Is it possible that GHC generates STG with invalid binding semantics for certain cases that the Cmm codegen fix or ignore?

This could explain my observations.

I've checked the Stg linter source (StgLint.hs ; GHC 8.2.2 and github master) and it does not check StgRhsClosure free var and binder list at all.

And the scope checker function (addInScopeVars) does not check for duplicates.

Any thoughts?

Cheers,

Csaba

On Sat, Nov 3, 2018 at 9:53 AM Csaba Hruska wrote:

Hi,

Can StgRhsClosure's freevar list ([occ]) or argument list ([bndr]) contain duplicates?

Cheers,

Csaba

data GenStgRhs bndr occ = StgRhsClosure CostCentreStack -- CCS to be attached (default is CurrentCCS) StgBinderInfo -- Info about how this binder is used (see below) *[occ]* -- non-global free vars; a list, rather than -- a set, because order is important !UpdateFlag -- ReEntrant | Updatable | SingleEntry *[bndr]* -- arguments; if empty, then not a function; -- as above, order is important. (GenStgExpr bndr occ) -- body